Bus Air Conditioning and Heating Unit

Bus Air Conditioning and Heating Unit Rearmount 68RM40-108 68RM40-118 68RM40-128 (with Electronic Thermostat)

OPERATION AND SERVICE MANUAL BUS AIR CONDITIONING AND HEATING UNIT Rearmount 68RM40-108 68RM40-118 68RM40-128 (with Electronic Thermostat) Carrier Transicold Division, Carrier Corporation, P.O. Box 4805, Syracuse, N.Y. 13221 Carrier Corporation 1998 D Printed in U. S. A. 1198

SAFETY SUMMARY GENERAL SAFETY NOTICES The following general safety notices supplement the specific warnings and cautions appearing elsewhere in this manual. They are recommended precautions that must be understood and applied during operation and maintenance of the equipment covered herein. The general safety notices are presented in the following three sections labeled: First Aid, Operating Precautions and Maintenance Precautions. A listing of the specific warnings and cautions appearing elsewhere in the manual follows the general safety notices. FIRST AID An injury, no matter how slight, should never go unattended. Always obtain first aid or medical attention immediately. OPERATING PRECAUTIONS Always wear safety glasses. Keep hands, clothing and tools clear of the evaporator and condenser fans. No work should be performed on the unit until all circuit breakers and start-stop switches are turned off, and power supply is disconnected. Always work in pairs. Never work on the equipment alone. In case of severe vibration or unusual noise, stop the unit and investigate. MAINTENANCE PRECAUTIONS Beware of unannounced starting of the evaporator and condenser fans. Do not open the condenser fan grille or evaporator access panels before turning power off, and disconnecting and securing the power plug. Be sure power is turned off before working on motors, controllers, solenoid valves and electrical control switches. Tag circuit breaker and power supply to prevent accidental energizing of circuit. Do not bypass any electrical safety devices, e.g. bridging an overload, or using any sort of jumper wires. Problems with the system should be diagnosed, and any necessary repairs performed, by qualified service personnel. When performing any arc welding on the unit, disconnect all wire harness connectors from the modules in the control box. Do not remove wire harness from the modules unless you are grounded to the unit frame with a static-safe wrist strap. In case of electrical fire, open circuit switch and extinguish with CO 2 (never use water). i

SPECIFIC WARNING AND CAUTION STATEMENTS SAFETY SUMMARY To help identify the label hazards on the Unit and explain the level of awareness each one carries, an explanation is given with the appropriate consequences: DANGER --- means an immediate hazard which WILL result in severe personal injury or death. WARNING --- means to warn against hazards or unsafe conditions which COULD result in severe personal injury or death. CAUTION --- means to warn against potential hazard or unsafe practice which COULD result in minor personal injury, product or property damage. The statements listed below are applicable to the refrigeration unit and may appear elsewhere in this manual. These recommended precautions must be understood and applied during operation and maintenance of the equipment covered herein. WARNING When servicing the unit, use caution when handling R-22 and R-134a. These refrigerants when in contact with high temperatures (about 1000_F) will decompose into highly corrosive and toxic compounds WARNING Be sure to avoid refrigerant coming in contact with the eyes. Should refrigerant come in contact with the eyes, wash eyes for minimum of 15 minutes with potable water only. THE USE OF MINERAL OIL OR REFRIGERANT OILS IS NOT RECOMMENDED. WARNING Be sure to avoid refrigerant coming in contact with the skin. Should refrigerant come in contact with the skin, it should be treated as if the skin had been frostbitten or frozen. WARNING Be sure ventilation in the workspace is adequate to keep the concentration of refrigerant below 1000 parts per million. If necessary, use portable blowers. WARNING Beware of rotating fan blades and unannounced starting of fans. WARNING Do not use a nitrogen cylinder without a pressure regulator and do not use oxygen in a refrigeration system, as an explosion could occur. WARNING Never fill a refrigerant cylinder beyond its rated capacity. Cylinder may rupture due to excessive pressure when exposed to high temperatures. WARNING When starting the unit, be sure that all manual refrigerant valves in the discharge line are open. Severe damage could occur from extremely high refrigerant pressures ii

TABLE OF CONTENTS Section SAFETY SUMMARY... Page i 1 DESCRIPTION... 1-1 1.1 Introduction... 1-1 1.2 Refrigeration System Component Specifications... 1-7 1.3 Electrical Specifications... 1-8 1.4 Safety Devices... 1-9 1.5 System Operating Controls and Components... 1-9 1.6 Heater Flow Cycle... 1-10 1.7 Air Conditioning Refrigerant Cycle... 1-11 2 OPERATION... 2-1 2.1 Starting and Stopping... 2-1 2.2 Pre-trip Inspection... 2-1 2.3 Unit Operation... 2-1 2.3.1 Cycling Clutch (Cool) - Automatic Mode... 2-1 2.3.2 Drivers Select Control - Cool Mode with Reheat... 2-3 2.3.3 Drivers Select Control - Vent Mode... 2-4 2.3.4 Drivers Select Control - Heat Mode... 2-4 3 TROUBLESHOOTING... 3-1 3.1 Unit Will Not Cool... 3-1 3.2 Unit Runs But Has Insufficient Cooling... 3-1 3.3 Abnormal Pressure... 3-1 3.4 Abnormal Noise and Vibrations... 3-2 3.4.1 Abnormal Noise... 3-2 3.4.2 Abnormal Vibration... 3-2 3.5 Thermostat Malfunction... 3-2 3.6 No Evaporator Air Flow or Restricted Air Flow... 3-2 3.7 Expansion Valve Malfunction... 3-2 3.8 No or Insufficient Heating... 3-3 4 SERVICE... 4-1 4.1 Maintenance Schedule... 4-1 4.2 Suction and Discharge Service Valves... 4-1 4.3 Installing Manifold Gauges... 4-1 4.4 Pumping The System Down or Removing the Refrigerant Charge... 4-3 4.4.1 System Pumpdown... 4-3 4.4.2 Removing the Refrigerant Charge... 4-3 4.5 Refrigerant Leak Check... 4-3 4.6 Evacuation and Dehydration... 4-3 4.7 Adding Refrigerant to System... 4-5 4.7.1 Adding Full Charge... 4-5 4.7.2 Adding Partial Charge... 4-5 4.8 Checking the Refrigerant Charge... 4-5 4.9 Checking For Noncondensables... 4-6 4.10 Checking and Replacing High or Low Pressure Cutout Switch... 4-6 4.10.1 Replacing High or Low Pressure Switch... 4-6 4.10.2 Checking High or Low Pressure Switch... 4-6 4.11 Filter-drier... 4-6 4.12 Thermostatic Expansion Valve... 4-7 4.13 Model 05G Compressor Maintenance... 4-8 4.13.1 Replacing the Compressor... 4-8 4.13.2 Checking the Compressor Oil Level... 4-9 4.13.3 Adding Oil to the Installed Compressor... 4-9 4.13.4 Adding Oil to Service Replacement Compressor... 4-10 4.13.5 Removing Oil from the Compressor... 4-10 4.13.6 Servicing Pressure Actuated Compressor Unloaders... 4-10 4.13.7 Electric Compressor Unloaders... 4-11 5 ELECTRICAL SCHEMATICS... 5-1 5.1 Introduction... 5-1 iii

LIST OF ILLUSTRATIONS Figure Page 1-1 Unit Assembly - Top and Back Views... 1-3 1-2 Unit Assembly - Inside View... 1-4 1-3 Unit Assembly - Heat Only Unit... 1-5 1-4 Electrical Control Panel Assemblies - All Except Heat Only Units... 1-6 1-5 Electrical Control Panel Assemblies - Heat Only Units... 1-7 1-6 Heater Flow Cycle... 1-10 1-7 Air Conditioning Refrigerant Cycle Flow Diagram for Systems Using R-134a... 1-11 1-8 Air Conditioning Refrigerant Cycle Flow Diagram for Systems Using R-22... 1-12 2-1 Unit Control Panel... 2-1 2-2 Thermostat Control Sequence During Cycling Clutch - Automatic Mode... 2-3 2-3 Thermostat Control Sequence Drivers Select Control - Cool Mode with Reheat.. 2-3 2-4 Thermostat Control Sequence Drivers Select Control - Vent Mode... 2-4 2-5 Thermostat Control Sequence Drivers Select Control - Heat Mode... 2-4 2-6 High Speed Fully Loaded Cool Mode Operation... 2-5 2-7 High Speed Unloaded Cool Mode Operation... 2-6 2-8 Low Speed Unloaded Cool Mode Operation... 2-7 2-9 Low Speed Vent Mode Operation... 2-8 2-10 Low Speed Heat Mode Operation... 2-9 2-11 High Speed Heat Mode Operation... 2-10 4-1 Suction or Discharge Service Valve... 4-1 4-2 R-134a Manifold Gauge Set Connections... 4-2 4-3 Evacuation Manifold... 4-4 4-4 Vacuum Pump Connections... 4-5 4-5 Checking High Pressure Switch... 4-6 4-6 Thermostatic Expansion Valve... 4-7 4-7 Model O5G Compressor... 4-8 4-8 Removing Bypass Piston Plug... 4-8 4-9 Compressor Oil Charge Connections... 4-10 4-10 Electric Unloader Schematic... 4-11 5-1 Electrical Control Panel Relay Board (RB) and Electronic Thermostat (TH) Outline Views... 5-1 5-2 Electrical Schematic (Model 68RM40-128-1, -13 or -14)... 5-2 5-3 Electrical Schematic (Model 68RM40-128-2)... 5-4 5-4 Electrical Schematic (Model 68RM40-128-3)... 5-6 5-5 Electrical Schematic (Model 68RM40-128-4)... 5-8 5-6 Electrical Schematic (Model 68RM40-128-6, -10 or -11)... 5-10 5-7 Electrical Schematic (Model 68RM40-108-1)... 5-12 5-8 Electrical Schematic (Model 68RM40-128-8 or -9)... 5-14 5-9 Electrical Schematic (Model 68RM40-108-5)... 5-16 5-10 Electrical Schematic (Model 68RM40-108-6)... 5-18 5-11 Electrical Schematic (Model 68RM40-108-4, -8 or -10)... 5-20 5-12 Electrical Schematic (Model 68RM40-108-2 or -3)... 5-22 5-13 Electrical Schematic (Model 68RM40-128-7 or -12)... 5-24 5-14 Electrical Schematic (Model 68RM40-108-7)... 5-26 5-15 Electrical Schematic (Model 68RM40-118)... 5-28 5-16 Electrical Schematic (Model 68RM40-108-9)... 5-30 5-17 Electrical Schematic (Model 68RM40-128-20)... 5-32 5-18 Electrical Schematic (Model 68RM40-128-23)... 5-34 5-19 Electrical Schematic (Model 68RM40-128-26)... 5-36 5-20 Electrical Schematic (Model 68RM40-128-27)... 5-38 5-21 Electrical Schematic (Model 68RM40-128-29)... 5-40 5-22 Electrical Schematic (Model 68RM40-128-32)... 5-42 iv

LIST OF TABLES Table Page 1-1 Part (Model) Number Chart... 1-2 1-2 Unloader Pressure Switch Settings... 1-8 1-3 Safety Devices... 1-9 4-1 R-22 Temperature - Pressure Chart... 4-12 4-2 R-134a Temperature - Pressure Chart... 4-13 v

SECTION 1 DESCRIPTION 1.1 INTRODUCTION This manual contains Operating and Electrical Data, and Service Instructions for the Model RM40A Bus Air Conditioning and Heating systems shown in the part (model)numberchartbelow. The RM40A unit is a one-piece system consisting of a condenser, evaporator and heater coil assemblies. The unit is installed in the rear A/C compartment of the bus. The RM40A unit interfaces with the air conditioning compressor, driver s switches, floor heater, water valves and pump to provide a complete air conditioning, heating and ventilation system. The RM40A unit has one type of thermostat, which in combination with a separate relay board, can control the unit in either a cycling clutch mode or reheat mode. (See Table 1-1.) In units configured for a cycling clutch, the compressor cycles on and off to control bus interior temperature. In units configured for reheat, the coolant valve opens or closes on thermostat command to control bus interior temperature, while the air conditioning mode continues to operate. 1-1

Table 1-1. Part (Model) Number Chart Part (Model) Refrigerant Thermostat Relay Board (RB) Configuration Evaporator and Condenser Blower Motors Schematic No. Figure Reference 68RM40-108-1 R-22 Adjustable Cycling Clutch Wound Field 68RM40-1248-6 5-7 68RM40-108-2 R-22 Adjustable Reheat Permanent Magnet 68RM40-1248-11 5-12 68RM40-108-3 R-22 Adjustable Cycling Clutch Permanent Magnet 68RM40-1248-11 5-12 68RM40-108-4 R-22 Fixed Reheat Wound Field 68RM40-1248-10 5-11 68RM40-108-5 R-22 Fixed Cycling Clutch Permanent Magnet 68RM40-1248-8 5-9 68RM40-108-6 R-22 Fixed Reheat Brushless 68RM40-1248-9 5-10 68RM40-108-7 R-22 Adjustable Reheat Wound Field 68RM40-1248-14 5-14 68RM40-108-8 R-22 Fixed Cycling Clutch Wound Field 68RM40-1248-10 5-11 68RM40-108-9 R-22 Adjustable Reheat Brushless 68RM40-1248-16 5-16 68RM40-108-10 R-22 Fixed Reheat Wound Field 68RM40-1248-10 5-11 68RM40-118 Permanent Magnet N/A Adjustable N/A (Heat Only) (Evap. Fan Motor Only) 68RM40-1248-15 5-15 68RM40-128-1 R-134a Fixed Cycling Clutch Brushless 68RM40-1248 5-2 68RM40-128-2 R-134a Adjustable Cycling Clutch Wound Field 68RM40-1248-1 5-3 68RM40-128-3 R-134a Adjustable Reheat Brushless 68RM40-1248-2 5-4 68RM40-128-4 R-134a Adjustable Reheat Wound Field 68RM40-1248-3 5-5 68RM40-128-6 R-134a Adjustable Reheat Permanent Magnet 68RM40-1248-4 5-6 68RM40-128-7 R-134a Adjustable Reheat Wound Field 68RM40-1248-13 5-13 68RM40-128-8 R-134a Fixed Reheat Permanent Magnet 68RM40-1248-7 5-8 68RM40-128-9 R-134a Fixed Reheat Permanent Magnet 68RM40-1248-7 5-8 68RM40-128-10 R-134a Adjustable Reheat Permanent Magnet 68RM40-1248-4 5-6 68RM40-128-11 R-134a Adjustable Reheat Permanent Magnet 68RM40-1248-4 5-6 68RM40-128-12 R-134a Adjustable Reheat Wound Field 68RM40-1248-13 5-13 68RM40-128-13 R-134a Fixed Cycling Clutch Brushless 68RM40-1248 5-2 68RM40-128-14 R-134a Fixed Cycling Clutch Brushless 68RM40-1248 5-2 68RM40-128-20 R-134a Fixed Reheat Wound Field 68RM40-1248-20 5-17 68RM40-128-23 R-134a Adjustable Reheat Brushless 68RM40-1248-21 5-18 68RM40-128-26 R-134a Adjustable Reheat Permanent Magnet 68RM40-1248-17 5-19 68RM40-128-27 R-134a Adjustable Reheat Wound Field 68RM40-1248-22 5-20 68RM40-128-29 R-134a Fixed Reheat Permanent Magnet 68RM40-1248-18 5-21 68RM40-128-32 R-134a Adjustable Reheat Wound Field 68RM40-1248-24 5-22 1-2

24 24 25 25 1 TOP VIEW BACK VIEW 26 1 ROADSIDE (RS) CURBSIDE (CS) 23 OUT IN 2 22 6 7 10 20 18 16 14 12 10 9 8 7 6 5 4 3 2 21 19 17 15 13 11 1. Condenser Coil Switch #1 (UPS1) 17. Filter-Drier 2. Evaporator Blower Housing 10. Heater Coil 18. Sight Glass and Blower Wheel (hidden) 11. Liquid-Suction Heat Exchanger 19. Receiver 3. DischargeLineCheckValve 12. Filter-Drier Outlet Valve 20. Fusible Plug 4. Discharge Line Shutoff Valve 13. Thermostatic Expansion Valve 21. Filter-Drier Inlet Valve 5. Discharge Line Connection (hidden from viewbehind panel) 23. Reheat Coolant Valve 22. Coolant Hookup Panel to Compressor 6. Condensate Drain Connection 14. Suction Line Connection 24. Condenser Fan Motor 7. Evaporator Blower Motor To Compressor 25. Condenser Fan Blade 8. Unloader Pressure 15. Condenser Fan Switch (CFS) 26. Low Ambient Thermostat Switch #2 (UPS2) 16. Unloader Pressure (LATH) 9. Unloader Pressure Switch #3 (UPS3) Figure 1-1. Unit Assembly ---Top and Back Views 1-3

1 2 3 (+) (--) 2 11 10 9 4 5 6 7 8 4 1. 440 Watt Resistor (Optional for Permanent Magnet Condenser Fan Motors Only) 2. Upper Mounting Bracket 3. Electrical Control Panel (See Figure 1-4.) 4. Evaporator Blower Wheel 5. Return Air Sensor 6. Return Air Filter 7. Return Air Filter Bracket 8. Evaporator Coil 9. Gauge Set (Optional) 10. 24 vdc Battery Cables 11. 24 vdc Electrical Interface Plug Figure 1-2. Unit Assembly - Inside View 1-4

1 ROADSIDE (RS) CURBSIDE (CS) 9 OUT IN 8 7 4 5 6 REAR BUS VIEW 5 4 3 2 (+) (--) 10 15 11 1. Blank Frame (Condenser) 2. Evaporator Blower Housing and Blower Wheel-Roadside 3. Access Panel 4. Blower Motor 5. Heater Coil INSIDE BUS VIEW 2 14 13 12 6. Access Panel 7. Coolant Hookup Panel 8. Evaporator Blower Housing and Blower Wheel-Curbside 9. Heater Coolant Valve 10. 24 vdc Electrical Interface Plug Figure 1-3. Unit Assembly - Heat Only Unit 9 11. 24 vdc Battery Cables 12. Evaporator Coil 13. Return Air Filter Bracket 14. Return Air Filter 15. Electrical Control Panel (See Figure 1-5.) 1-5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 16 21 20 15 18 WOUND FIELD MOTORS 17 1 3 4 5 6 7 8 9 10 11 12 13 16 21 20 15 18 PERMANENT MAGNET MOTORS 17 19 3 5 7 8 9 10 11 12 13 16 21 20 15 18 BRUSHLESS MOTORS 17 1. Condenser Speed Relay (CSR) 12. Circuit Breaker #6 (CB6) 2. Evaporator Speed Relay (ESR) 13. Temperature Selector (Optional) 3. Evaporator Fan Relay #1 (EFR1) 14. Hourmeter (Optional) 4. Evaporator Fan Relay #2 (EFR2) 15. Power Terminal Block 5. Condenser fan Relay #1 (CFR1) 16. Blower Relay (BR) 6. Condenser fan Relay #2 (CFR2) 17. Electronic Thermostat (TH) 7. Circuit Breaker #1 (CB1) 18. Relay Board (RB) 8. Circuit Breaker #3 (CB3) 19. Evaporator Speed Relay (ESR) 9. Circuit Breaker #2 (CB2) 20. Floor Blower Relay Lockout (FBRL) 10. Circuit Breaker #4 (CB5) 21. Floor Blower Relay (FBR) 11. Circuit Breaker #5 (CB6) Figure 1-4. Electrical Control Panel Assemblies - All Except Heat Only Units 1-6

1 2 3 4 5 6 7 8 18 17 16 15 9 14 13 12 11 10 1. Evaporator Fan Relay #1 (EFR1) 10. Evaporator Speed Relay #1 (ESR1) 2. Evaporator Fan Relay #2 (EFR2) 11. Electronic Thermostat (TH) 3. Circuit Breaker CB#1 (CB1) 12. Terminal Block, 10-Pole 4. Circuit Breaker CB#3 (CB3) 13. Diode (D3) 5. Circuit Breaker CB#2 (CB2) 14. Blower Relay (BR) 6. Temperature Selector 15. Evaporator Overload Relay #2 (OR2) 7. Diode (D5) 16 Evaporator Overload Relay #1 (OR1) 8. Diode (D6) 17. Floor Blower Relay (FBR) 9. Power Terminal Block 18. Boost Pump Relay (BPR) Figure 1-5. Electrical Control Panel Assembly - Heat Only Units 1.2 REFRIGERATION SYSTEM COMPONENT SPECIFICATIONS a. Refrigeration Charge R-22: R-134a: b. Compressor 16 lb (7.26 kg) 24 lb (10.88 kg) Model: 05G No. of Cylinder: 6 Weight (Dry): 145 lb (66 kg) including clutch Oil Charge: New Compressor: 6.75 pints (3.2 liters) Replacement Compressor: 5.5 pints (2.6 liters) Oil Level: Old Crankcase (before S/N 4994J): Bottom to 1/4 of sight glass New Crankcase (beginning S/N 4994J): Between Min---Max marks on crankcase Approved Compressor Oils - R-22: Calumet Refining Co.:R030 Texaco : WF68 Witco: 4GS Suniso Approved Compressor Oils - R-134a: Castrol: Icematic SW68C Mobil: EAL Artic 68 ICI: Emkarate RL68H c. 05G Compressor Electric Unloader Pressure Switches UPS1, UPS2 & UPS3 (See Table 1-2.) d. Thermostatic Expansion Valve R-22 Units Superheat Setting: 12 3_F (6.7 1.7_C) MOP Setting: 95.5 7 psig(6.7 0.47 kg/cm@) R-134a Units Superheat Setting: 11 3_F (6.7 1.7_C) MOP Setting: 65 4 psig(3.8 0.36 kg/cm@) e. Low Pressure Switch (LPS) Opens at: 6 3 psig(0.42 0.27 kg/cm@) Closes at: 25 3 psig(2.8 0.27 kg/cm@) f. High Pressure Switch (HPS) R-22 Units Opens at: 425 10 psig (30 0.7 kg/cm@) Closes at: 300 10 psig (21 0.7 kg/cm@) R-134a Units Opens at: 300 10 psig (21 0.7 kg/cm@) Closes at: 200 10 psig (14 0.7 kg/cm@) g. Condenser Fan Switch (CFS) R-22 Units Closes for High Speed: 360 10 psig (25.2 0.7 kg/cm@) Opens for Low Speed: 285 15 psig (20.0 1.1 kg/cm@) 1-7

R-134a Units Opens for High Speed: 250 10psig (17.6 0.7 kg/cm@) Closes for Low Speed: 190 15 psig (13.4 1.1 kg/cm@) h. Water Temperature Switch (WTS) (Customer Supplied) i. Low Ambient Thermostat (LATH) Opens at: 45 3_F (7.2 1.7_C) Closes at: 55 5_F (12.8 2.8_C) j. Unit Weight Approximate: 640 lb (290 kg) 1.3 ELECTRICAL SPECIFICATIONS a. Evaporator/Heater Blower Motors Brushless Motor Bearing Lubrication: Factory Lubricated (additional grease not required) Horsepower: 0.75 (1.0 kw) Full Load Amps (FLA): 25 amps Operating Speed: High Speed: 1800 rpm Low Speed: 1600 rpm Voltage: 24 vdc Permanent Magnet Motor Bearing Lubrication: Factory Lubricated (additional grease not required) Horsepower: 0.75 (1.0 kw) Full Load Amps (FLA): 27 amps Operating Speed: 1800 rpm Voltage: 27 vdc Wound Field Motor Bearing Lubrication: Factory Lubricated (additional grease not required) Horsepower: 0.8/0.5 (1.1/0.67 kw) Full Load Amps (FLA): 28/24 amps Operating Speed: 1800/1400 rpm Voltage: 27 vdc b. Condenser Fan Motor Brushless Motor Bearing Lubrication: Factory Lubricated (additional grease not required) Horsepower: 0.5 hp (0.67 kw) Full Load Amps (FLA): 17 amps Operating Speed: High Speed: 1550 rpm Low Speed: 1000 rpm Voltage: 24 vdc Permanent Magnet Motor Bearing Lubrication: Factory Lubricated (additional grease not required) Horsepower: 0.75 hp (1.0 kw) Full Load Amps (FLA): 27 amps Operating Speed: 1800 rpm Voltage: 27 vdc Wound Field 2-Speed Motor Bearing Lubrication: Factory Lubricated (additional grease not required) Horsepower: 0.75/0.25 (1.0/0.34 kw) Full Load Amps (FLA): 21/13 amps Operating Speed: 1600/1200 rpm Voltage: 27 vdc Table 1-2. Unloader Pressure Switch Settings UNLOADER PRESSURE SWITCH-Contacts Open/Close Settings [psig(kg/cm@)] UPS1 UPS2 UPS3 Refrigerant Load Up (Opens) Unload (Closes) Load Up (Opens) Unload (Closes) Load Up (Opens) Unload (Closes) R-22 66 2 (4.6 0.14) 54 2 (3.8 0.14) 61 2 (4.3 0.14) 51 2 (3.6 0.14) 325 15 (23 1.1) 400 10 (28 0.7) R-134a 35 3 (2.5 0.21) 26 2 (1.8 0.14) 31 2 (2.2 0.14) 23 2 (1.6 0.14) 220 15 (19 1.1) 275 15 (19 1.1) 1-8

1.4 SAFETY DEVICES System components are protected from damage caused by unsafe operating conditions with safety devices. (See Table 1-3.) During the A/C mode, the compressor will automatically stop if the HPS or LPS switch contacts open due to an unsafe operating condition. Opening HPS or LPS contacts de-energizes the A/C compressor clutch. The A/C Stop Light will also illuminate indicating that an unsafe operating condition has occurred. The evaporator blower motors and condenser fans will continue to run. During any mode of operation (A/C, Vent or Heat), operation will automatically stop if the bus circuit breaker (CB29) senses excessive current draw. The evaporator, condenser and floor heater motors are protected independently against high current draw with circuit breakers (CB1,2,3, 4, and 5). The wound field and permanent magnet evaporator and condenser fan motors are also protected by an internal overload thermostat. If one or both of the evaporator motor safety devices opens to stop the evaporator fan motor(s), the system may develop a low pressure condition which may cause the low pressure switch (LPS) to open, shutting the compressor down. If a condenser fan motor safety device opens to stop the condenser fan motor(s), the system may develop a high pressure condition, which may open the high pressure switch (HPS) to shut the compressor down. When a safety device opens and causes the unit operation to stop, place the climate control switch to off position before resolving the problem. The safety device may need to be manually reset before restarting the unit. 1.5 SYSTEM OPERATING CONTROLS AND COMPONENTS a. Electronic Thermostat (TH) The RM40A unit has one type of thermostat, which operates in combination with a separate relay board to control the operation of the unit in a cycling clutch mode or a reheat mode. (See Table 1-1.) In units configured for a cycling clutch, the compressor cycles on and off to control bus interior temperature. In units configured for reheat, the Reheat Coolant Valve (RCV) opens or closes on thermostat command to control bus interior temperature, while the air conditioning mode continues to operate. The setpoint of the thermostat is either manually set (adjustable) or factory set (fixed). (See Table 1-1.) The thermostat s temperature sensor monitors the bus interior temperature at the return air section of the unit and controls the operating function of the system to maintain the bus interior temperature at the setpoint. Table 1-3. Safety Devices Unsafe Condition Safety Device Device Setting 1. Excessive current draw by the 1. Circuit Breaker --- CB1 1. Opens at 20 amps floor heater blowers and boost pump. Manual Reset 2. Excessive current draw by 2. Circuit Breaker --- CB2 2. Opens at 40 amps evaporator motor no.1. Manual Reset 3. Excessive current draw by 3. Circuit Breaker --- CB3 3. Opens at 40 amps evaporator motor no. 2. Manual Reset 4. Excessive current draw by 4. Circuit Breaker --- CB4 4. Opens at 40 amps condenser motor no. 2. Manual Reset 5. Excessive current draw by 5. Circuit Breaker --- CB5 5. Opens at 40 amps condenser motor no.1. Manual Reset 6. Excessive current draw by the 6. Circuit Breaker --- CB6 6. Opens at 10 amps clutch coil. Manual Reset 7. High compressor 7. High Pressure Switch (HPS) 7. Refer to Section 1.2 discharge pressure. Manual Reset 8. Loss of refrigerant charge 8. Low Pressure Switch (LPS) 8. Opens at 6 3psig Manual Reset (0.42 0.21 kg/cm@) 1-9

The Electronic Thermostat (TH) regulates the operational cycles of the unit by energizing or de-energizing four interior relays to control low or high speed cool, low or high speed heat or vent and unloaded or loaded cool operational modes in response to deviations in bus interior temperature relative to the thermostatsetpoint.(seefigure5-1.)onerelaycontrols the operation of Unloader Valve #1 (UV1). Another controls low or high speed evaporator fan operation. Another activates the cool cycle and the other relay activates the heat cycle. Refer to Section 2 for description of operational control sequences for the various operational modes. b. Manual Switches A/C Mode Switch (ACMS) ---Supplied by OEM The A/C Mode Switch (ACMS), which is located on the driver s control panel, activates the operation of the unit. When the switch is closed, 24 vdc is fed from the circuit breaker (CB29) through the ACMS switch to feed power to terminal B5 (Connector B) on the relay board. Defrost Switch (DFS) ---Supplied by OEM The Defrost Switch (DFS) will manually energize the Boost Pump Relay (BPR) to activate the boost pump motor. c. Thermal Switches Water Temperature Switch (WTS) ---Supplied by OEM The Water Temperature Switch (WTS) is located on the block of the vehicle engine and senses the vehicle engine coolant temperature. The WTS is a normally closed switch that opens on temperature rise at 120_F (49_C). When the vehicle water temperature is below 120_F, the switch is closed, completing a circuit for the Blower Relay (BR); this switch prevents the circulation of cooler air throughout the bus during the initial start-up of the vehicle and unit. Condenser Motor Overloads (COL1 and COL2) - Used on Wound Field and Permanent Magnet Motors Only Each condenser motor is equipped with an internal overload thermostat. If excessive motor temperature exists, the COL switch will open to de-energize the corresponding motor contactor; this will stop the affected condenser motor. Evaporator Motor Overloads (EOL1 and EOL2) - Used on Wound Field and Permanent Magnet Motors Only Each evaporator blower motor is equipped with an internal overload thermostat. If either motor experiences excessive temperature, the corresponding EOL switch will open to de-energize the OR relay coil opening the OR relay contacts; this de-energizes the ESR1 relay, which forces the unaffected evaporator fan motor into high speed. Freeze Protection Temperature Switch (FPTS)---(Optional) The switch operates off the thermostat to interrupt power to the A/C compressor clutch when low evaporator coil temperature occurs. d. Pressure Switches Condenser Fan Switch (CFS) TheCondenserFanSwitch(CFS)islocatedonthe inlet line to the receiver. When the condenser coil refrigerant pressure reaches 360 10 psig (25.3 0.7 kg/cm@) forr-22 or250 10 psig (17.6 0.7 kg/cm@) for R-134a, CFS switch will either open or close on pressure rise (depending on the unit model) to energize or de-energize the motor contactor and control the speed of the condenser fan motors; this will lock the Condenser Fan Motors (CM1 and CM2) in high speed until the refrigerant pressure in the condenser coil drops to 285 15 psig (20 1.1 kg/cm@) forr-22or190 15 psig (13.4 1.1 kg/cm@) for R-134a, resuming low speed operation. (See wiring schematics in Section 5 for specific wiring differences.) 1.6 HEATER FLOW CYCLE Heating is controlled by the thermostat which controls the operation of the Reheat Coolant Valve (RCV). When the reheat water valve solenoid is energized, the valve will open to allow engine coolant to flow through the heater coil. 6 1 5 1. Heater Coil 2. Reheat Coolant Valve 3. Outlet Tube 4. Inlet Tube 5. Inlet Hose 6. Outlet Hose Figure 1-6. Heater Flow Cycle 2 3 4 1-10

1.7 AIR CONDITIONING REFRIGERANT CYCLE When air conditioning is selected, the unit operates as a vapor compression system using R-22 or R-134a as a refrigerant. The main components of the system are the reciprocating compressor, air-cooled condenser coil, thermostatic expansion valve, and evaporator coil. Systems using R-134a also incorporate a Liquid-Suction Heat Exchanger (LSHX). The compressor raises the pressure and the temperature of the refrigerant and forces it into the condenser tubes. The condenser fan circulates surrounding air (which is at a temperature lower than the refrigerant) over the outside of the condenser tubes. Heat transfer is established from the refrigerant (inside the tubes) to the condenser air (flowing over the tubes). Thecondensertubeshavefinsdesignedtoimprovethe transfer of heat from the refrigerant gas to the air. This removal of heat causes the refrigerant to liquefy; thus liquid refrigerant leaves the condenser and flows to the receiver. The receiver serves as a liquid refrigerant reservoir so that a constant supply of liquid is available to the evaporator as needed, and acts as a storage space when pumping down the system. The receiver is equipped with a sight glass to observe the refrigerant for restricted flow and correct charge level. The refrigerant leaves the receiver and flows through the manual receiver outlet valve, and the through a filter-drier where an absorbent keeps the refrigerant clean and dry. From the filter-drier, the liquid refrigerant flows through the subcooler where it is subcooled before entering the liquid-suction heat exchanger The Liquid-Suction Heat Exchanger (LSHX), used on R-134a systems only, increases system operating efficiency by subcooling liquid refrigerant before it enters the thermal expansion valve; this reduces flash gas. It also serves to ensure there is no liquid refrigerant in the suction vapor returning to the compressor. If there is low temperature liquid refrigerant present in the suction line returning to the compressor, it will evaporate in the heat exchanger due heat absorbed from the liquid line. The liquid then flows to a thermostatic expansion valve which reduces pressure and temperature of the liquid and meters the flow of liquid refrigerant to the evaporator to obtain maximum use of the evaporator heat transfer surface. The low pressure, low temperature liquid that flows into the evaporator tubes is colder than the air that is circulated over the evaporator tubes by the evaporator blower. Heat transfer is established from the evaporator air (flowing over the tubes) to the refrigerant (inside the tubes). The evaporator tubes have aluminum fins to increase heat transfer from the air to the refrigerant; therefore the cooler air is circulated to the interior of the bus. The transfer of heat from the air to the low temperature liquid refrigerant in the evaporator causes the liquid to vaporize. This low temperature, low pressure vapor passes through the suction line. The low pressure refrigerant vapor is now drawn into the compressor where the cycle repeats. When ventilation only is selected only the evaporator blowers function to circulate air throughout the bus. The refrigerant cycle will remain off. 4 12 10 11 6 13 5 7 UPS1 UPS2 19 20 11 1. Compressor 2. Discharge Line 3.DischargeLineCheckValve 18 4. Condenser Coil 5. Receiver 6. Filter-Drier Inlet Valve 7. Filter-Drier 8. Filter-Drier Outlet Valve 9. Thermostatic Expansion Valve 10. Evaporator Coil 11. Suction Line 12. Subcooler 13. Liquid-Suction Heat Exchanger 14. Condenser Fan Switch (CFS) 15. Unloader Pressure Switch (UPS3) 16. Charge Isolation Valve 17. Discharge Service Port 18. Suction Service Port 19. Unloader Pressure Switch (UPS2) 20. Unloader Pressure Switch (UPS1) 21. Liquid Solenoid Valve (LSV) Figure 1-7. Air Conditioning Refrigerant Cycle Flow Diagram for Systems Using R-134a 8 CFS 14 UPS3 15 9 21 16 3 2 17 1 1-11

4 12 10 9 20 11 6 7 UPS1 UPS2 8 CFS UPS3 19 18 13 14 3 5 15 11 2 1. Compressor 2. Discharge Line 3.DischargeLineCheckValve 4. Condenser Coil 5. Receiver 6. Filter-Drier Inlet Valve 7. Filter-Drier 8. Filter-Drier Outlet Valve 9. Thermostatic Expansion Valve 10. Evaporator Coil 11. Suction Line 12. Subcooler 13. Condenser Fan Switch (CFS) 14. Unloader Pressure Switch (UPS3) 15. Charge Isolation Valve 16. Discharge Service Port 17. Suction Service Port 18. Unloader Pressure Switch (UPS2) 19. Unloader Pressure Switch (UPS1) 20. Liquid Solenoid Valve (LSV) - (Not Installed on All units) 17 Figure 1-8. Air Conditioning Refrigerant Cycle Flow Diagram for Systems Using R-22 16 1 1-12

SECTION 2 OPERATION 2.1 STARTING AND STOPPING a. Starting NOTE Theenginecoolantmustbewarmenoughto open the customer-supplied Water Temperature Switch (WTS) for unit operation to start. 1. Start the vehicle engine. 2. If the unit is supplied with an automatic driver control, place the customer supplied A/C Mode Switch (ACMS), located on the driver s switch panel, in the ON position. If the unit is supplied with a driver s select control, place the A/C Mode Switch (ACMS) in the desired mode of operation position (HEAT, COOL, VENT or OFF). b. Stopping NOTE Be sure the air conditioning unit is turned off before stopping the vehicle engine. select the mode of operation depending on the internal bus temperature. (See Figure 2-1.) The drive s select control consists of a rotary switch withheat,cool,ventandoffpositions,which allows the driver to select the mode of operation. The thermostat will still operate automatically to maintain the required setpoint temperature. (See Figure 2-1.) AUTOMATIC DRIVER CLIMATE CONTROL SWITCH 1. Place the customer supplied A/C Mode Switch (ACMS) to the OFF position. 2.2 PRE-TRIP INSPECTION After starting unit, allow system to stabilize (10 to 15 minutes) and proceed as follows: 1. Listen for abnormal noises. 2. Check compressor oil level. 3. Check refrigerant level. 2.3 UNIT OPERATION The RM40A unit has a temperature controlling Electronic Thermostat (TH), which in combination with a separate relay board, can control the bus internal temperature in either a cycling clutch mode or reheat mode. (See Table 1-1.) The relay board is factory wired to customer specifications for one of these two modes. In units configured for a cycling clutch, the compressor cycles on and off to control bus interior temperature. In units configured for reheat, the reheat coolant valve opens or closes on thermostat command to control bus interior temperature while the air conditioning mode continues to operate. There are two driver s control options available: a driver s select control and a driver s automatic control. The controls are located on the driver s switch panel and are designated A/C Mode Switch (ACMS) on the electrical schematics. The driver s automatic control consists of a toggle switch with ON and OFF positions, which, when in the ON position, allows the thermostat to automatically DRIVER SELECT CLIMATE CONTROL SWITCH Figure 2-1. Unit Control Panel The thermostat is available with an adjustable or fixed (factory-set) setpoint. (See Table 1-1.) The unit control circuits and components operate on 24 vdc power supplied by the bus battery or alternator. 2.3.1 Cycling Clutch (Cool) - Automatic Mode (See Figure 2-2.) To operate in the cycling clutch automatic mode of operation, the A/C Mode Switch (ACMS) is placed in the ONposition.WiththisswitchintheONpositionand 24 vdc power available from the bus battery or alternator, Electronic Thermostat (TH) automatically determines whether heating, cooling or ventilation is required to regulate vehicle interior temperature. When the bus is running and the batteries are charging, 24 vdc power is also applied to Power Terminal Block (PTB) to operate fan motors and compressor clutch. When the ACMS switch is placed in the ON position, power is applied to energize A/C Relay (ACR) and Heat Relay (HR). Power is also applied to terminal B5 on the relay board, which makes power available to terminal L4 of the Electronic Thermostat (TH) and to energize Evaporator Fan Relay #1 (EFR1). Energizing relay ACR closes a set of normally open ACR contacts, which allows the thermostat to control the cooling circuit components. 2-1

Energizing relay HR closes a set of normally open HR contacts, which allows the thermostat to control the heating circuit components. Energizing relay EFR1 closes a set of normally open EFR1 contacts to power Evaporator Fan Motors (EM1 and EM2). Upon rising and falling interior bus temperatures, the the thermostat control sequence during the automatic cycling clutch mode is as follows: a. Also, from terminal B5, power is available to energize Fault Relay (FR) provided a high or low refrigerant pressure condition does not exist. Energizing relay FR closes a set of normally open FR contacts in the circuit to Compressor Clutch (CL) and opens a set of normally closed FR contacts in the circuit to A/C Stop Relays #1 and #2 (ACSR1 and ACSR2). When the system is in the cooling mode, the Compressor Clutch (CL) is energized through closed FR, CFR1, ACSR1 and CR contacts. The open set of FR contacts keeps A/C Stop Relays #1 and #2 (ACSR1 and ACSR2) de-energized as long as system refrigerant pressures (high and low) are at values that keep switches closed. (See Table 1-2.) If High Pressure Switch (HPS) or Low Pressure Switch (LPS) contacts open, relay FR de-energizes to disengage the refrigerant compressor clutch and illuminate the A/C Stop Light. b. When the vehicle s interior temperature rises to 3 F below the thermostat setpoint, the thermostat switches from high speed heat mode to low speed heat mode. (See Figure 2-10.) In the low speed heat mode, the thermostat remains in the HEAT position and switches from HIGH to LOW position for low speed fan operation. The heating control circuit is activated by applying power, through closed HR contacts, to energize Reheat Coolant Valve (RCV) solenoid, Floor Blower Relay (FBR), Boost Pump Relay (BPR) and the customer- supplied Sidewall Water Valve (SWV). Energizing Boost Pump Relay (BPR) closes normally open BPR contacts to start Boost Pump Motor. Energizing Floor Blower Relay (FBR) closes normally open FBR contacts to start floor blowers. Energizing Reheat Coolant Valve (RCV) solenoid opens the valve and starts the flow of engine coolant through the heating coils for heating. When the thermostat switches from HIGH to LOW, power is applied to both sides of evaporator fan motor coils EMC1 and EMC2 to change both evaporator fan motors (brushless motors) from high speed to low speed operation. c. When the vehicle s interior temperature rises to the thermostat setpoint, the thermostat switches from low speed heat mode to low speed vent mode. (See Figure 2-9.) In the low speed vent mode, the thermostat remains in the LOW position and switches from HEAT position to a neutral position; this deactivates the heating control circuit by removing power from the heating control circuit components. The cooling control circuit remains deactivated and the evaporator fans continue to operate on low speed. d. When the vehicle s interior temperature rises to 1 F above the thermostat setpoint, the thermostat switches from low speed vent mode to low speed unloaded cool mode. (See Figure 2-8.) In the low speed unloaded cool mode, the thermostat is in the UNLOAD position and switches from the neutral position to the COOL position; this activates the cooling control circuit by applying power, through closed ACR contacts, to energize Condenser Fan Relay #1 (CFR1) and Clutch Relay (CR). Power is also applied to one side of condenser fan motor coils CM1 and CM2. Energizing Clutch Relay (CR) closes a set of normally open CR contacts to activate the Compressor Clutch (CL), through closed FR and ACR1 contacts; this starts the air conditioning compressor. Energizing relay CFR1 closes a set of normally open CFR1 contacts to power Condenser Fan Motors (CM1 and CM2). e. With power applied to both sides of the CMC1 and CMC2 coils, through the Condenser Fan Switch (CFS) contacts, the condenser fan motors will operate on low speed. During cooling operation, when Condenser Fan Switch (CFS) opens due to high condensing pressure, power is removed from one side of the coils and the condenser fans will then operate on high speed. With the thermostat in the UNLOAD position, power is applied to Unloader Valve #1 (UPS1) solenoid to energize the coil. Energizing the coil causes the compressor to unload one bank (two cylinders). Valve UV1 can also be controlled by Unloader Pressure Switch #1 (UPS1). If suction pressure falls to the setpoint of switch UPS1, switch contacts close to energize valve UV1 and unload one compressor cylinder bank. An additional unloader valve (UV2), controlled by either Unloader Pressure Switch #2 (UPS2) or Unloader Pressure Switch #3 (UPS3), loads or unloads another bank of cylinders. Switch UPS2 senses refrigerant suction pressure and switch UPS3 senses refrigerant discharge pressure. (See Table 1-2.) f. When the vehicle s interior temperature rises to 3 F above the thermostat setpoint, the thermostat switches from low speed cool mode to high speed cool mode. (See Figure 2-7.) In the low speed cool mode, the thermostat remains in the COOL position and switches to HIGH position for fan speed, changing evaporator fan motor operation from low speed to high speed by removing power from one side of the evaporator fan motor coils. The compressor remains unloaded with two cylinders not operating. g. When the vehicle s interior temperature rises to 5 F above the thermostat setpoint, the thermostat remains in the COOL and HIGH positions and switches to LOAD position; this fully loads the refrigerant compressor by de-energizing Unloader Valve (UV1) solenoid coil. (See Figure 2-6.) The compressor is now operating on all six cylinders. h. On a falling temperature, except for a 2 F differential, thermostat control sequence changes in reverse to the above. (See Figure 2-2.) 2-2

3 FABOVE SETPOINT 1 FABOVE SETPOINT SETPOINT 1 F BELOW SETPOINT 2 F BELOW SETPOINT HIGH SPEED, FULLY LOADED COOL HIGH SPEED, UNLOADED COOL LOW SPEED UNLOADED COOL LOW SPEED VENT LOW SPEED HEAT RISING TEMPERATURE 5 FABOVE SETPOINT 3 FABOVE SETPOINT 1 FABOVE SETPOINT SETPOINT 3 F BELOW SETPOINT Upon rising and falling interior bus temperatures, the thermostat control sequence, during the driver select control - cool with reheat mode, is as follows: a. When the bus interior temperature rises to the thermostat setpoint, the thermostat deactivates the heating cycle by removing power from the heating control circuit. The system is now operating in low speed unloaded cool mode. Refer to section 2.3.1d. and e. for status of controls while in this mode. b. When the bus interior temperature rises to 3 F above the thermostat setpoint, the thermostat switches from low speed unloaded cool to high speed unloaded cool. Refer to section 2.3.1f. for a description of control action. c. When the bus interior temperature rises to 5 F above the thermostat setpoint, the thermostat switches from high speed unloaded cool to high speed fully loaded cool. Refer to section 2.3.1g. for a description of control action. d. Upon a falling temperature, the thermostat control sequence changes in reverse to the above. See Figure 2-3 for control points. 5 FBELOW SETPOINT HIGH SPEED HEAT RISING TEMPERATURE FALLING TEMPERATURE Figure 2-2. Thermostat Control Sequence During Cycling Clutch - Automatic Mode HIGH SPEED, FULLY LOADED COOL 5 FABOVE SETPOINT 2.3.2 Driver Select Control - Cool Mode with Reheat (See Figures 2-3.) With the driver select control (A/C Mode Switch ACMS) in the COOL position and with Relay Board (RB) configured for reheat, the unit will operate on continuous cooling and the heating control circuit will be activated or deactivated on thermostat demand. 3 FABOVE SETPOINT HIGH SPEED, UNLOADED COOL 3 FABOVE SETPOINT 1 FABOVE SETPOINT SETPOINT LOW SPEED UNLOADED COOL SETPOINT Placing the ACMS switch in the COOL position energizes A/C Relay (ACR), closing a set of normally open ACR contacts. Power is also applied to terminal B5, which applies power to Relay Board (RB). Because of jumpers installed on the terminal board, power is applied from the relay board to the cooling control circuit through ACR closed contacts. 2 F BELOW SETPOINT LOW SPEED UNLOADED COOL WITH REHEAT Power is also applied to Evaporator Fan Relays #1 and #2 (EFR1 and EFR2), which closes contacts to power Evaporator Fan Motors #1 and #2 (EM1 and EM2). Refer to section 2.3.1a. for other control actions. The Heat Relay (HR) cannot be energized with the ACMS switch in the COOL position. However, jumpers on the relay board enable the thermostat to apply power to the heating control circuit upon demand for heating. FALLING TEMPERATURE Figure 2-3. Thermostat Control Sequence Drivers Select Control - Cool Mode with Reheat 2-3

2.3.3 Drivers Select Control - Vent Mode (See Figure 2-4.) With the driver select control (A/C Mode Switch ACMS) in the VENT position, A/C Relay (ACR) and Heat Relay (HR) cannot be energized. Therefore, the heating and cooling circuits cannot be activated. The system now operates in the vent mode only. Placing switch ACMS in the VENT position applies power to relay board terminal B5 to energize Evaporator Fan Relay #1 (EFR1), closing EFR1 normally open contacts to power the evaporator fan motors. When the bus interior temperature rises to 3 Fbelow the thermostat setpoint, the thermostat switches from high to low speed vent mode. In this mode, the thermostat switches to the LOW position to apply power to the other side of evaporator fan motor coils EM1 and EM2. With power applied to both sides of these coils, the fan motors operate in low speed. (See Figure 2-9.) When the bus interior temperature rises to 3 Fabove the thermostat setpoint, the thermostat switches from low to high speed vent mode. In this mode, the thermostat switches to the HIGH position to remove power from one side of evaporator fan motor coils EMC1 and EMC2. With power removed from one side of these coils, the fan motors operate in high Speed. Upon a falling temperature, the thermostat control sequence changes in reverse to the above. See Figure 2-4 for control points. HIGH SPEED VENT RISING TEMPERATURE 3 F ABOVE SETPOINT 2.3.4 Driver Select Control - Heat Mode (See Figure 2-5.) With the driver select control (A/C Mode Switch ACMS) in the HEAT position, Heat Relay (HR) is energized to close a set of normally open HR contacts allowing the thermostat to control the heating control circuit. With the ACMS switch in the HEAT position, the A/C Relay (ACR) cannot be energized. Therefore, the cooling circuit cannot be activated. When the bus interior temperature falls to 2 Fbelow the thermostat setpoint, the thermostat switches from the low speed vent mode to low speed heat mode. In the low speed heat mode, the thermostat switches to the HEAT position. Switching to the HEAT position, applies power to the heating control circuit to activate the heating cycle. The thermostat remains in the LOW position to operate the evaporator fan motors on low speed. When the bus interior temperature falls to 5 Fbelow the thermostat setpoint, the thermostat switches from low speed heat mode to high speed heat mode. In the high speed heat mode, the thermostat switches to HIGH position to remove power from one side of evaporator fan motor coils EM1 and EM2. With power from one side of these coils, the fan motors operate on high speed. (See Figure 2-11.) The thermostat remains in the HEAT position. Upon a rising temperature, the thermostat control sequence changes in reverse to the above. See Figure 2-5 for control points. RISING TEMPERATURE 1 F ABOVE SETPOINT SETPOINT LOW SPEED VENT SETPOINT SETPOINT SETPOINT LOW SPEED VENT 2 F BELOW SETPOINT LOW SPEED HEAT 3 F BELOW SETPOINT 3 F BELOW SETPOINT 5 FBELOW SETPOINT HIGH SPEED HEAT 5 FBELOW SETPOINT HIGH SPEED VENT FALLING TEMPERATURE FALLING TEMPERATURE Figure 2-4. Thermostat Control Sequence Drivers Select Control - Vent Mode Figure 2-5. Thermostat Control Sequence Drivers Select Control - Heat Mode 2-4

(PTB2) =Energized Circuit =De-energized Circuit Figure 2-6. High Speed Fully Loaded Cool Mode Operation 2-5

=Energized Circuit =De-energized Circuit Figure 2-7. High Speed Unloaded Cool Mode Operation 2-6

=Energized Circuit =De-energized Circuit Figure 2-8. Low Speed Unloaded Cool Mode Operation 2-7

=Energized Circuit =De-energized Circuit Figure 2-9. Low Speed Vent Mode Operation 2-8

=Energized Circuit =De-energized Circuit Figure 2-10. Low Speed Heat Mode Operation 2-9

=Energized Circuit =De-energized Circuit Figure 2-11. High Speed Heat Mode Operation 2-10

SECTION 3 TROUBLESHOOTING INDICATION/ REFERENCE TROUBLE POSSIBLE CAUSES SECTION 3.1 UNIT WILL NOT COOL Compressor will not run V-Belt loose or defective Check Compressor malfunction See Note Clutch malfunction Check/Replace Safety device open 1.4 Electrical malfunction A/C mode switch defective Check Circuit Breaker open Check/Reset Thermostat malfunction 3.5 Water Temperature Switch (WTS) Closed Check 3.2 UNIT RUNS BUT HAS INSUFFICIENT COOLING Compressor Compressor valves defective See Note V-belt loose Check Refrigeration system Abnormal pressures 3.3 No or restricted evaporator air flow 3.6 Expansion valve malfunction 3.7 Restricted refrigerant flow 3.7 & 4.10 Low refrigerant charge 4.5 & 4.7 Service valves partially closed Open Safety device open 1.4 Coolant Valve Stuck Open Check 3.3 ABNORMAL PRESSURE High discharge pressure Refrigerant overcharge 4.4 Noncondensibles in system Check Pressure Condenserfanmotorrotationincorrect Check Condenser coil dirty Clean Low discharge pressure Compressor valves(s) worn or broken See Note Low refrigerant charge 4.5 & 4.7 High suction pressure Compressor valves worn or broken See Note Low suction pressure Suction service valve partially closed Open Filter-drier inlet or outlet valves partially closed Check/Open Filter-drier partially plugged 4.10 Low refrigerant charge 4.5 & 4.7 Expansion valve malfunction 3.7 Restricted air flow 3.6 Low evaporator air flow Blower running in reverse Check Dirty air filter Clean Icing of coil Clean Suction and discharge pressures Compressor valves defective See Note tend to equalize when unit is operating NOTE: Refer to 05G Compressor manual, Form 62-02756. 3-1