Replaced my AC compressor this summer and its been a tad weird since-
With heat on, outside-to-inside air flow, the ac compressor will constantly go on for 1 second then go off for 20 seconds or so. I've read how compressors are supposed to engage every so ofter to cycle the system, but this seems quite often.
With heat on, if i press the recirculate button the ac compressor immediately turns on and stays on.
No matter if i turn the ac button on/off it does not engage/disengage the compressor.
How does this happen?
We have a 2001 Malibu, and here is what I observed when I adjusted the settings on my climate control attempting to recreate your problem. Here's what I gathered.
The AC compressor should not engage unless the following modes are activated:
AC button depressed
Recirculate engaged (in any function and thermostat adjustment)
Defrost or defrost/floor mode
Defrost/recirculate engages the AC for safety reasons; to keep humidity down and help clear humidity inside the windows on very humid days, and happens by default as stated by a previous poster. I have read, but am not entirely sure, that this is required by the NHTSA on vehicles made after the mid to late 90's.
The AC did not engage in any of the other modes including heat on fresh air intake, at least not on any other chevy I have access to. I have heard of high failure rates of the internal electronics inside of the thermostat control module on these cars, causing the AC to engage or not engage correctly or at weird times, and I have even seen instances where the AC light actually flashes when depressed.
As for the quick engagement and disengagement of the AC clutch, how well does your AC perform during the summer? It could be possible that your AC performs so well that the AC is disengaged quickly because it is reaching it's set temp to prevent freezing over. Though, doubtful since the compressor wouldn't be on long enough to de-humidify the air when defrost or recirculate was activated.
Some reason's (that I can think of) for unnecessary AC clutch engagement.
Faulty control board:
As said above, they fail more frequently than they should. It would probably pay to find a known working one from a friend's car of similar make/model or cheap pull from a junk yard to see if your problems aleviate. This is my bet, since the thermostat control is electronic, and isn't supposed to allow engagement of the AC in fresh air intake. It could also be stuck on recirculate even though the fresh light is illuminated.
Electrical short or loose connection:
It is possible that when replacing the compressor or over time of the car, that a wire was accidentally pinched, grazed, scraped, etc and allowing jacket to expose and the wire to touch ground and engage the AC. I have heard of shorts and lose connections causing quite the assortment of weird problems, and have encountered one or two puzzling ones myself.
I hope my information is useful and pertains well to the subject matter. Thanks all!