AC Clutch on?
#1
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89 S4. Assuming factory parts, does the AC clutch cycle on/off, or does it stay engaged as long as the HVAC/AC system is on? Preliminary speaking it seems that mine is turning as long as the AC button is "On" and the temp lever is "on". I should mention it was converted to R134 at some point by one of the many PO's. Thanks.
#2
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It stays on unless certain undesirable conditions occur, such as: your evaporator freezes up, which can occur because of freeze switch malfunction, high humidity, low evaporator air flow, or low refrigerant. There is a coolant sensor that shuts off a/c with over temp. Some models have a pressure switch that would turn off the compressor clutch for under or over pressures. Even modern cars often use this arrangement for humidity control.
Good luck,
Dave
Good luck,
Dave
Last edited by j.kenzie@sbcglobal.net; 05-25-2020 at 01:54 PM.
#3
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There are - on S4+ - exactly two devices in between the ‘button’ in the HVAC head and the compressor clutch that are designed to interrupt the circuit:
- low pressure switch (the device on the bottom of the tube from the condenser.)
- anti-freeze switch
If your A/C functions as it should with sub-30°F vent temperatures then a functional anti-freeze switch will periodically interrupt the clutch circuit.
If your A/C functions poorly then the anti-freeze switch may never open.
If your A/C functions but ices the evaporator then the freeze switch is dead.
New freeze switches need to be check/calibrated. And they last 10 years +/- 5 years (it seems...)
- low pressure switch (the device on the bottom of the tube from the condenser.)
- anti-freeze switch
If your A/C functions as it should with sub-30°F vent temperatures then a functional anti-freeze switch will periodically interrupt the clutch circuit.
If your A/C functions poorly then the anti-freeze switch may never open.
If your A/C functions but ices the evaporator then the freeze switch is dead.
New freeze switches need to be check/calibrated. And they last 10 years +/- 5 years (it seems...)
#4
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Thanks for the quick and clear answers. Fumbling towards diagnosing the AC issues....TBC
#5
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FYI, I was able to remove and test my freeze switch on ice water and properly calibrate it. It was slightly out of adjustment.
new freeze switches are fairly inexpensive as well.
new freeze switches are fairly inexpensive as well.