How To: Maintain your APU

The air filter on the climate control unit of a Carrier Transicold ComfortPro APU cleans air for heating or cooling.

Auxiliary power units add to truck maintenance chores, though they can partly make up for it by extending your oil change and engine overhaul intervals. Follow these basics:

  • Change the engine oil and filter at manufacturers’ recommended intervals, typically 1,000 hours. At the same time, check belts for proper tension and condition. Cracks, glazing or excessive stretch are signs they need replacement.
  • Change the fuel filter at the recommended interval, which may or may not be aligned with oil change hours.
  • Inspect the air cleaner at the recommended interval. If dirty, change it.
  • If the engine has a cooling system separate from the truck engine, change coolant at recommended intervals or at the first sign of cloudiness in the coolant or deposits inside the radiator. If the main engine coolant also cools the APU engine, just maintain the main engine’s cooling system. When changing main engine coolant, make sure to bleed air from the APU system until full, or its engine could be destroyed.
  1. The air filter on the climate control unit of a Carrier Transicold ComfortPro APU cleans air for heating or cooling. This type of filter should be inspected at oil change intervals and cleaned if necessary. If a pleated paper or similar filter is used, change it when it becomes obviously clogged. Check your owner’s manual for details.
  2. Cleaning the ComfortPro air cleaner normally doesn’t work, so replace it when dirty. To replace the air cleaner, which is located at bottom, remove the covering and slide out the unit. That also gives you access to the blue spin-on engine oil filter (lower right). The large belt on the left drives the 120-volt generator, and the smaller one on the right drives the cooling fan. Check both for tension and condition at every oil change.
  3. The sight glass on top of the receiver-drier on a ComfortPro unit should be checked for obvious bubbles, indicating a probable low charge or problem with the internal refrigeration system. Have the system recharged if bubbles appear. Some sight glasses also have an indicator that changes color if moisture gets into the system; in that case, evacuate and recharge the system and replace the drier.
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