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I don't use the AC in my 94 VX very much since it really kills the mileage.
I believe the system adjusts the compressor cycling frequency based on temp selection.
You could check to see if the heater control valve is allowing hot water to circulate to the heater core by touching the supply and return hoses to see if hot coolant is actually circulating. On the coldest temp setting I don't think it is circulating.
The way I use my AC is to use the lowest fan setting, max cool and recirculate. If the air is still to cool you can manually cycle the compressor on and off until the air stops coming out of the dash any cooler.
Another way to get the most out of your AC without it costing any fuel, is to cycle the compressor on when you are using DFCO. Since there is no fuel used in DFCO the AC compressor activity is free. Any time you use engine braking, turn the compressor on to cool off the evaporator, then turn it off when you are accelerating or driving at a constant speed. You can leave the fan on until the evaporator has cooled off to the point where the air coming out of the vents is no cooler than the outside air.
Think of it as pulse and gliding the compressor to minimize the energy used to cool the evaporator. The engine idle speed will stay at its normal low setting if the fan speed is less than 2.
More modern cars have seen dramatic changes in the way AC compressors work. Some of them do not even have a clutch anymore. They work by variable displacement in the compressor itself to control pressures in the system, based on demand, and are probably more efficient than you might think.
The systems that mix hot an cold air for climate control usually have a max air setting that can be selected with a low fan speed for best efficiency.
regards
Mech
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