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re: Re: TQC heater core replacement (Now A/C info)

> The 4000 cars probably use an A/C system that runs the compressor all the 
> time and then regulate the evaporator pressure to control the amount of 
> cooling.

The 4000 uses a cycling clutch, operated by a thermostat that senses 
evaporator temperature.  Very traditional, low-cost AC implementation.

> The 5000 cars use a Cycling Clutch Orifice Tube (CCOT) system (from 
> General  Motors ie Cadillac) that turns the compressor on and off to 
> regulate the evaporator temp. There is an orifice tube (no evaporator 
> valve) that is used to somewhat regulate the flow of liquid freon into the 
> evaporator where it expands and absorbs heat from the interior of the 
> vehicle.

I'm not familiar with this animal.  GM's older system uses both an expansion 
valve on the evaporator inlet and a POA (pilot-operated-absolute) valve on the 
evaporator outlet to control evaporator pressure to the desired level.  The 
compressor runs all the time the AC is on in this type of system.  The system 
had excellent performance without the annoying loading/unloading of the engine,
and was used by Rolls-Royce, Mercedes, Lincoln, and others.