It depends on the APU. If you have an APU controller at the head of the sleeper bed with buttons, look for a button that says something like "oppt hours". If you have one of the newer APU controllers with just three knobs, look in the storage compartment on the side of your truck for a small electronic box that shows your APU hours.
These are the two types that I've dealt with. Sorry I'm not too savvy at uploading pictures here yet.
On tractor trailers, and APU is a small diesel engine that powers a heat and air conditioning unit while charging the truck's main batteries at the same time. This allows the driver to remain comfortable in the cab and have access to electric power without running the main truck engine.
Having an APU helps save money in fuel costs and saves wear and tear on the main engine, though they tend to be expensive to install and maintain. Therefore only a very small percentage of the trucks on the road today come equipped with an APU.
Thank you for the information
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