Truck APU Buying Guide Written by Jonathan Kovey of Promax APUs

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1 Truck APU Buying Guide Written by Jonathan Kovey of Promax APUs When buying an APU, most drivers do a large amount of research to decide which one is the best match for their needs. The problem that many run into is not knowing what exactly that research should entail. APU specifications are important, but don t let them mislead you. Just because an APU states that it puts out 35,000 BTUs, it may not heat any better than one that puts out 10,000. This article has been written to share my years of APU manufacturing, engineering, assembling, and installing knowledge. Why Buy an APU? An APU is a big investment. $6,000-12,000 is no small potatoes. You can buy a decent car for that kind of money. So why should you invest in an APU? Well there s only one reason. Money. In the short run, plopping down a few thousand dollars is tough, but in the long run, savings on fuel and maintenance will quickly pay it back. How fast that payback is depends on how often you plan on using it and which one you buy, but most drivers can figure the payback period is within months. This can be easily computed from the fuel savings, which tend to be roughly 1/6 of what they would be if you were idling your main engine. The maintenance costs are tougher to calculate, but any time you can turn off your main engine is less time you have to worry about causing unneeded wear and tear. 2 Cylinder vs. 3 Cylinder Probably the most important decision when buying an APU is deciding whether to get a 2 or 3 cylinder engine. There are tradeoffs to both, but usually only one of these is right for your truck. There are single cylinder engines on the market. I have not included them in this guide for the sole reason that I do not think they are powerful enough to fulfill the needs of the average trucker. The following is a breakdown (to the best of my ability) of the main differences between 2 and 3 cylinder engines: 2 Cylinder 3 Cylinder Cheaper Faster RPMs (more vibration) Smaller Footprint Less Heating/Cooling Power Low Power Output More Expensive Slower RPMs (less vibration) Bigger Footprint More Heating/Cooling Power High Power Output So which one should you buy? If you have the frame rail space and are willing to spend the extra money (usually ~$1000 more) I always recommend buying a 3 cylinder. Trucks with large sleepers (>200 ft 3 area) especially will require the larger APU. If space is an issue, or you have a smaller cab, a 2 cylinder will do the job; just don t expect as much power as what you ll get from a larger unit. Most 3 cylinder engines will require between of clean frame rail space to be mounted on. I always recommend a few inches extra on either side to also be able to work on maintaining the unit when necessary. If you have less than 24, then I would highly recommend a 2 cylinder. Warranty As with any product, an APU s quality is usually best defined by its warranty. The standard for the industry is 1 year on parts and 3 years on the engine. If you can find a higher one, I d strongly recommend it over buying a unit that is otherwise equal.

2 Digital vs. Analog I would argue that the biggest problem with APUs on the market is their durability. Many manufacturers build a beautiful looking showroom product that only fails as soon as it sees a year on the road. A big portion of the problems that APU owners run into is due to their system being digital. If a control board goes bad, all of a sudden it s the trucker s responsibility to pay the $800 to replace it. So, why don t all APU manufacturers use an analog system? The following breakdown should help display the differences of an analog vs. a digital system. Analog Cheap (think $4 switch if it goes bad) Non- programmable thermostat Bulkier control panel (usually 2 deep) Wire bundle connection Digital Expensive (think $800 board if it goes bad) Programmable thermostat Slimmer control panel (usually 3/4 deep) Ethernet (usually) cord connection BTUs BTUs (British Thermal Units) are a standard of measurement for heating and cooling. Most APUs on the market will have between 10,000 and 35,000. The higher the BTUs, the more capability the system has to put out higher heat/cooler AC. Most 2 cylinder engines will have lower BTUs than similar 3 cylinder models. This is one of the main reasons I suggest that trucks with bigger sleepers have 3 cylinder APUs. Most drivers will be comfortable with 25,000+ BTUs. This really doesn t become a big issue until you get into weather below 30 degrees or above 90. The bottom line here is that the more BTUs your APU has, the more comfortable you ll be. Vent Placement If I had to pick the second biggest problem with APUs on the market, I would say it is how many vents the average APU uses and where they are placed. In the beginning of the article I noted how it was possible for a 10,000 BTU heater to heat better than a 35,000 BTU. This is because of the way they are vented. 1 vent putting out a lot of hot air will do a whole lot less than 4 vents putting out a lesser amount of hot air. Think of vents like windows in a house. If you open 1 window on a warm summer day, you ll get a nice breeze within a certain area close to that window. Open 4 windows and all of a sudden the whole house has a nice breeze. Manufacturers do not put the number of vents they install on their websites; you will have to ask them. Just as important is where the vents are placed in the sleeper. Let s go back to the window example; if you open 4 windows on one side of the house, you re not getting much circulation. Open them on multiple sides, and all of a sudden the air circulates much better. Make sure that if you have 4 vents, you have 2 high and 2 low. Make sure that these are as spread out as possible to ensure maximum circulation. CFMs The specifications of most APU manufacturers will list the CFMs the unit puts out. CFMs are cubic feet per minute of air output through the HVAC blower. The higher the CFMs, the more air it can push out. Higher CFMs also mean a bigger HVAC unit that will have to be put in your bunk. Anything 600 CFM or

3 more will take care of even the biggest sleeper. These are similar to BTUs, the more CFM of air your APU can put out, the more comfortable you ll be. For anything over 500 CFMs, make sure you have ~22 x22 of open under- the- bunk space where you can put the HVAC unit. For anything less you can figure for one about half this size. Just remember though, the smaller the HVAC, the less comfortable it will be able to keep you in sub- 30 or over- 90 degree weather. Generator vs. Alternator Many APUs on the market have a generator. I would caution drivers about generators. Generators on APUs are an offshoot from the RV industry (where APUs began). The problem is that they just don t handle the dirt and grime of the road as well as an alternator. That s not to say that they re not an option, but if you buy an APU with a generator, make sure to keep it absolutely clean or else you risk an expensive generator replacement. An alternator paired with an inverter is a much better option. They tend to handle the rigors of the road more so than generators. The argument can be made that an inverter can be dangerous to truck batteries. This is easily negated with an inline fuse that blows if the inverter draws too much amperage. Make sure if the APU you buy has an inverter, that it also has a fuse. There are many alternator options in the APU market. Manufacturers have everything from 40 amps to 210 amps. Think of anything less than 100 amps as a trickle charger. They will keep your power steady, but won t build up your batteries very quickly. Anything higher will keep your power steady and charge your batteries. The higher the amperage, the faster your batteries will charge. It will take the best alternator on the market about 30 minutes to fully charge your batteries. A small alternator can take all day. Materials/ Design An APU s quality will only be as good as its materials and design. An APU that is made from plastic parts will never be able to handle the stress of the road. Make sure that all external surfaces are metal. Bolts should all be grade 8. These are easily recognizable by their golden color and their unique 6 dashes on the bolt head. Any bolts that aren t grade 8 will corrode in a year and break off when unfastened. Beware of anything that is mounted externally other than the main APU box. There are many APUs on the market that mount the condenser, radiator, fan, or muffler externally. All of these will obviously be exposed to the elements, including rocks. A rock through the condenser puts it out of service pretty quick. If you do go with a unit that has one of these mounted externally, make sure that they put it in a place that is unlikely to see many rocks. However, be wary of mounting any of these on the back of the cab. This will cause the cab to vibrate and may prove unbearable while sleeping. Ensure that anything mounted outside of the main APU box is covered under warranty, or else be prepared to have to pay to replace it. There are 2 ways that most APUs are mounted: bolting to the frame, or clamping to the frame. Both of these work well and neither is really better than the other. Clamping to the frame will take up more space and bolting to the frame will require 4 holes to be drilled in it. Many drivers worry about the structural integrity of drilling into the frame. I have asked multiple engineers about this issue and they have all told me that there is no worry in drilling (4) ¾ holes into a truck frame. It does not weaken the integrity of the frame.

4 Maintenance Upkeep on an APU is vital. These are small engines that take a lot of abuse on the road and then have to run at fairly high RPMs. Most manufacturers prescribe to a 1000 hour maintenance schedule. This means that every 1000 hours a driver will need to change the oil, oil filter, fuel filter, air filter, and water separator. This is the standard time given by the base engine manufacturer. Usually 1000 hours will be between 4-6 months. In addition to this, it is important to regularly check antifreeze and oil levels on at least a weekly basis. Beware of any APU that deviates from this 1000 hour standard. Any more and you re probably voiding the engine s warranty. Any less and you don t have a quality engine. The biggest problem I see when it comes to maintenance on APUs is actually cleanliness. These engines are usually boxed in and therefore once water or road dust get in, they ll have to be washed out from the inside. If this doesn t happen on a regularly basis, oxidation and corrosion will obviously occur much quicker. I recommend cleaning out the inside of your APU as often as you clean your truck. Total Cost of Ownership So let s say that you do go out and buy an APU, what should you expect the costs to be? Obviously the main chunk of change will be the initial price. A good 2- cylinder APU can be had for ~$7000 and a good 3- cylinder will be ~$8000. Obviously prices will be all over the board, but expect to pay somewhere in that range. If a price seems too good to be true, look at the parts. Make sure that you re only buying a quality APU that isn t going to break after a month on the road. The next cost to factor in is maintenance. The regularly scheduled maintenance interval (usually miles) will consist of replacing oil and all filters. Figure this to cost ~$60 after all s said and done in just parts. Some guys will skimp on replacing all the filters. Just trust me when I say don t skimp on the maintenance. As most of you know, maintain it now and you won t have to pay to fix it later. Most drivers can figure that this scheduled maintenance will be every 4-6 months. The biggest variable on cost with APUs is the after- install repairs. Anytime anything goes wrong on the APU, it takes time out of your schedule to not only have to identify the problem, but then the entire truck will be down while you have to go to a shop to have it repaired. Check with other owners of APUs before you buy a specific brand to find out how often they have had problems. If an APU is in the shop more than twice a year, there s a serious problem with the design. That said, if you re already driving through the area, it never hurts to stop in at the APU installer s shop just so they can give the unit a look over. The more research you do now, the more likely you ll be to pick a reliable unit. The final cost is fuel. For almost all APUs, the fuel savings over idling will be ~75-85%. Most trucks will idle at gallons per hour. The average APU will burn between.15 and.25 gph. Inverter This probably doesn t fall under the buying guide of an APU, but I think it s important to cover. When buying an inverter, most drivers don t realize there are 3 fairly distinct different types. (Cheap) modified sine wave, modified sine wave, and pure sine wave. Technically both of the modified sine waves are the same type, but the difference in quality between each is huge. The following compares each: (Cheap) Modified Sine Wave Modified Sine Wave Pure Sine Wave Inexpensive (<$200) Moderate Price($300- $1000) Expensive ($600- $2000) Lots of interference Little interference No interference

5 Small footprint Medium footprint Medium footprint So what is interference? The interference caused by each refers to the type of wave signal that each has. The cheaper the inverter, the worse the amount of interference you ll likely see. If you plug into an inverter with high amounts of interference, your TV signal will look shaky, your DVD picture won t look clear, and you could even get interference over your CB. A cheap modified sine wave inverter can be found at a fuel stop for under $200. I strongly discourage drivers from buying these. A decent modified sine wave inverter can be had for around $400. A good pure sine wave inverter will be at least $800. The amount of power you need will vary on your usage, but a 2000 watt inverter should do the trick if all you re running is a fridge, computer, TV, and cell phone charger. Many drivers forget that most inverters can be mounted sideways. One of the best space savers under the bunk is to mount the inverter sideways on a wall so that its footprint is half of what it would have been lying flat If you have any comments or questions on this article or anything at all related to buying APUs, feel free to contact the writer at: info@promaxapu.com. God Bless.