RE: Ambulance air conditioning
I have a friend who has worked on many different makes of ambulance, and he told me that the only thing in common on ambulances, is that there's nothing common (unless it was required by KKK-1822). Every maker does things their own way, and every ambulance electrician also puts their own spin on things. When I asked him about heating and cooling systems, he said that nothing surprises him anymore. So, what I found out may or may not point others in the right direction.
But for what it's worth-
In my own case, when I picked up my ambulance at GEV and started home, I wasn't too happy with the AC, and the heater appeared to have a valve closed. They became a question for later. When later happened, I tried tracing out the heater lines, and found that it appeared that the cab heat looked like it was supplied by the module (the ambulance portion), which kinda made sense. Then, in a burst of intelligence, I remembered the switch on the dash panel that said "Heat - A/C". When I turned it on, I suddenly heard a pump running, and when I started the beast, I had heat. When I tried AC, I had much more AC, probably because the large under-body Hoseline condenser was now running.
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I finally figured out that the module thermostat had to be set correctly for the cab to benefit - if the module's thermostat didn't call for heat or AC, the cab wouldn't get any heat or AC, but if the module was heating or cooling, then the cab benefited, and the cab heat/AC controls could be used to adjust the cab temperatures