Operators have a choice today of battery powered cooling systems combined with a fuel-fired heater, or the diesel-engine-based systems that either provide power for an electric AC compressor or drive a compressor independent of the truck's HVAC system. The systems have come a long way since the first commercially available units hit the streets in the late 1980s. Upfront costs have come down significantly, and reliability and efficiency have both improved as well.
As is the case with anything mechanical, no matter how well it's put together, it won't run forever without a little attention.
Itamar Levine, the director of maintenance and purchasing at Bison Transport in Winnipeg, Manitoba, says when his company first went down the APU road more than a decade ago, they were lasting only weeks because of the corrosive anti-icing material used on highways.
"Without exaggerating, each unit we had went through four of five radiators in three years," he says. "Exhaust systems would last two or three months before they flew off the truck. We had a technician in each of our shops who did nothing but service and repair APUs."
Levine notes with some relief that current models have proven much more reliable. So while each APU may not need as much parts and service as it used to, because there are more APUs on the road today, it means there's strong and growing demand for replacement parts, consumables, and service.
Levine's advice for a long and happy relationship with an APU is to buy a premium product, and service it with premium parts.
"Synthetic oil, for example, will improve cold starting capability, and ensure good lubrication, just in case you go over the service interval," he says. "Stick to the recommended maintenance intervals, don't scrimp on the materials, and maintain a good relationship with the product's service manager."
Engine-based systems are more maintenance-intensive than battery powered systems, but both require a little care and attention every now and then. Depending on the manufacturer's recommended service intervals, the engine-based systems will need at least oil, filters, and possibly drive belts.
APU maker Carrier recommends for its ComfortPro APU an oil and filter change at 1,000 hours, along with a valve-lash adjustment. There are also specific points that need cleaning and/or inspection, such as the radiator and condenser fins. At 500 hours, Carrier suggests inspections of the fuel system, coolant hoses and clamps, belt tension and alignment, a chassis inspection including the exhaust system, mounts etc., and an air filter inspection.
The 2,000-hour inspection is a more comprehensive service interval requiring, among other things, examining the performance parameters of the fuel injectors, generator and alternator output, starter, and HVAC system.
In general terms, Carrier's Dean Lande tells us, "The 1,000-hour service is a six-month interval for a typical over-the-road operator, the 2,000-hour service is an annual event."
Established maintenance intervals aside, to keep an APU running, you have to consider where it lives - hanging on a truck frame. You won't find a more hostile environment anywhere, with constant vibration, occasional jolting impacts, corrosive road spray, and extreme heat and cold.
Most APU failures can be traced back to one or more of these factors. Since you can't eliminate them, the best you can do is guard against component damage.
That means keeping a close eye out during regular service inspections for physical problems such as cracks forming on the component mounts, and around the radiators, mufflers, and other external bits. Be wary of possible contamination and corrosion, especially on the seals and connectors.
Dwayne Cowan, product manager for auxiliary power units at Thermo King, suggests keeping a close eye on the mounting brackets and the connectors leading to and from the unit.
"Anything you can do to reduce costs is going to improve the ROI, and chassis inspections and maintenance are high on the list - in addition to the scheduled service events," he says. "Our coolant and refrigerant loops are factory sealed and require no routine maintenance, but don't ignore them. Leaks can develop, hoses can become chafed, and any of that could result in failure."
There is usually about 2 pounds of refrigerant in the system, and unless a leak develops, there's no need to top up the systems. If the refrigerant level needs to be adjusted, federal law requires the work be done by an EPA-licensed HVAC technician with the proper tools to avoid accidental refrigerant discharge.
"Regular and thorough washing is highly recommended. Electrical connections should be sealed with dielectric grease and then left alone. Opening the connector renders them prone to incursion," Cowan adds.
In addition to the chassis and engine service, PMs should include a check of the condensate drain to ensure the fittings aren't clogged. If the customer has a split system with an external condensing unit, inspect and clean any debris from the condenser coil to ensure good air flow, Dometic advises.
Battery-powered systems, on the other hand, require few consumables and service requirements are basically just visual inspections.
The next wave
Since it's the engine that requires the majority of the maintenance on a diesel APU, take away the engine, and you're left with batteries. Stand-alone HVAC systems do not use traditional lead-acid batteries, so you don't have the usual battery maintenance, either. Instead, Advanced Glass Mat (AGM) batteries are the power supply of choice, and these require no maintenance beyond ensuring the connectors are tight and the cable is in good condition.
In short, there's not much that can go wrong with a battery-powered system.
"There's not much on the original Nite system that could fail, except perhaps a fan motor or something," says Bill Gordon, Bergstrom's national director of aftermarket. "Our new Nite Phoenix system has an air filter that requires annual replacement, but that's really it."
Bergstrom was one of the pioneers in battery-powered on-board climate control systems. Its Nite HVAC system was adopted by several OEMs as a data book option. The company raised the stakes this year, introducing the first no-engine climate control system powered by lithium-ion battery.
Gordon says the single Li-ion battery is 63 percent lighter (110 pounds) than a three-pack AGM system, takes up 20 percent less space on the truck, and it produces 16 percent more power. Additionally, the Li-ion battery has zero memory effect, which helps maintain optimum charge and recycle performance over a longer lifespan than AGM batteries.
While Gordon admits the Li-ion batteries are more expensive upfront, he says the system remains competitively priced, and will actually prove less costly over the life of the unit.
"When you look at the efficiency of the system, and the replacement costs and life cycles of AGM batteries, a Li-ion battery makes the value proposition. We cool for longer, for less, we charge faster, and over the life of the system, we're about 20 percent less expensive," he says.
In a revealing move, Thermo King released a battery-powered version of its Tri-Pac APU at the