A/C Problem ac control shut off and on and blows hot air when i got it worked good. I replaced it 2 times with a used one and it sell did not work.

Maby a bad a/c control panel. Or the wiring harness is shot. I would check wires for good connectivity and no burnt wires, and check all of the fuses for a start

I would make sure the shut off valve between the cold air and warm air is engaging. this is controlled by a vacume

What do you mean when you say it wont shut off? is it blowing hot air or do you just feel a lite flow of hot air even if you have the settings to cold?

If this is the problem that you always feel hot air at low flow and the ac goes to hot air then i would say one of two things, first if you have the selector to cold and you feel hot air then there may be a problem with the blend door, this door move to allow hot or cold air, the door may be broken or just a bad motor that controls it. keep in mind if the ac system shuts down for any reason the air then will be warm, it will be about the same temp as outside and maybe a little hotter.

this problem almost sounds like the ac compressor shuts off and then you are getting the outside air which is hot, there are many reasons for the compressor to shut off, it could be the compressor clutch heating up and disengaging , this would be due to a bad compressor clutch.

another reason is the fans are not working, the best thing to do is when the system starts to blow warm check and see if the compressor is running, start engine and look at the front of compressor, with ac off the front of it will not move, and then with ac on the front will spin, check it out and let me know, if it blows warm air and ac is not working then it may be compressor problem but if you are getting warm air and the compressor is spinning then it may be a door problem.

This is hard to check with out testing the system, so i listed a few things to check and let me know the out come. also the ac blows cold for how long before it gets hot air blowing out of the vents, good day.

take it to an accredited ac specialist shop and have it checked for leaks
sound like it was gassed up to sell it and after you got it the gas has leaked out

It sounds like you have a blend door issue.Try cycling the air to blow on different parts of the cab ie: defrost,to floor to vent.if you have cold air blowing good on all selections and you know your motor is working on all speeds,then you have a blend door not opening.The control for that is behind the heater/ac control unit.They do go bad from time to time.You can pick up a replacement at either a dealer or a Auto Parts place that sells GM or AC DELCO parts.

I would check the following possibilities:
1. Is compressor clutch working? - You need to do this when the ac is blowing hot air only - locate compressor drive pulley on engine - rubber belt wraps around it. Start engine and set to max ac. When the ac is blowing hot air, look at the center of the compressor drive pulley using a good flash light - watch it for a while, it should be spinning with the pulley - this means the compressor is engaged. If not, the compressor is not engaged. If your ac is blowing hot air, then the compressor should be engaged and running (trying to cool). If it is not engaged, then your compressor clutch is probably going out. Could be low voltage to clutch, but more likely the clutch is worn out and only working some of the time. Note: if working normally, the compressor clutch will engage and disengage in cycles- but the air should always be cold. If clutch is bad, compressor would need to be replaced (sold as one unit). This is tricky to diagnose and could take some time - you need to do it when ac is blowing hot air but set to max cooling.

2. Low on refrigerant or refrigerant has moisture in it? If your ac blows cold initially after being off for a while, then heats up, and continues to regularly cycle back and forth between hot and cool air, then the system may be low on refrigerant or the refrigerant may have moisture in it that is freezing and restricting refrigerant flow. An a/c shop can check refrigerant level and even replace refrigerant if moisture is suspected.

Could be other issues, but I would start with these.

Good luck

I had the same problem but it was blowing hot air on the passenger side of the car. I assume you have the dual zone controls that I have as well. The problem is most likely the damper that controls the flow of hot and cold air into the car. The motorized component of the damper is most likely not working and its stuck in the hot air position.

I had mine replaced by a repair shop so I cant tell you how to replace it but it may be something that you can do if you have the time and patience to work on it.

Good luck

THE BLEND DOOR THAT CONTROLS HOT TO COLD SWITCHING IS STICKING. THE CONTORL HEAD IS ELECTRIC AND MAY BE CAUSING THE PROBLEM. HEAT AND AC ARE 2 COMPLETELY DIFFERENT SYSTEMS EXCEPT FOR THE CONTROLLER UNDER YOUR RADIO. HEATER COIL IS REALLY A HEATER CORE WHICH IS A LITTLE RADIATOR INSIDE THE CAR BEHIND THE DASHBOARD.

Sounds like your temperature actuator is not moving or your temp door is broken. On max a-c ,coolant is shut off to your heater core allowing only cold air in.

Check the resistor pack/board on the cabin fan