By Jerry Lemon, Lemco Mobile AC Consulting
Welcome to the new world of HD and off-road air conditioning. There was a time, not that long ago, when the HVAC system in a piece of heavy equipment, or an over-the-road (OTR) truck, was as simple as it could be made to be. Compressor, condenser, expansion valve, evaporator, and a drier or accumulator (sometimes both, really). Controls were equally simple – blower switch with a clutch post (that was the one labelled C), thermostat (with a probe into the coil – or in some cases, wrapped around the suction tube at the outlet of the evaporator), pressure switch (or switches – low, high and fan override, at most), and the compressor field coil. The simplest ones were connected in series with the single wire clutch grounding through the body of the compressor to complete the circuit. Others, such as Caterpillar, used a two-wire clutch and ground through the pressure switch and thermostat to complete the circuit. Regardless of the system in the not too distant past, they were simple enough to be drawn out on a single sheet of paper – both the mechanical and electrical sides. We used to laugh at the automotive service people with their vacuum controls, body control modules, multiple computer systems and everything else involved with A/C service.
Well, it has now come full circle to envelop all of us in the Off-Road and HD OTR air conditioning service industry. We are witness to fully blown, module controlled, HVAC with automatic climate control on demand (ATC – Automatic Temperature Control) built into the equipment at a factory level. The only difference is that now the automotive service guys are laughing at us. Why? Because they have the right to service the vehicles – which means that the manufacturers are required to make the diagnostics available for use. The HD OTR trucks and the Off-Road equipment manufacturers are not required to provide us with the necessary tools, and purchasing a suite of diagnostics that will enable us do these jobs run into the thousands of dollars, plus annual license fees. If we… to read more….CLICK HERE