A/C stops working randomly

[Nemesis1990]

Hello everyone, I have a 2002 GMC Yukon XL with the Auto Climate Control. I purchased the truck last year and the AC would never work. The guy that was filling it up for me told me that it's the compressor. When you click the A/C button it would flash 3 times then nothing. I purchased a NEW GM AC Compressor and installed it and it started working ICE COLD!. A few days later I was going to work and turned on the AC and the button flashed 3 times and nothing. I started driving to work and in about 10-15 minutes the AC kicked on and I had cold air again. And on some days Ill have AC and then randomly it will shut off and when I press the button again it would flash 3 times and nothing until I keep driving and eventually it would turn back on. This was towards the end of summer in GA so I did do some diag. I checked the Relay, and all Fuses associated with the AC system and they were all good. Jumped the Low Pressure switch and that didnt work as well as the sensor thats in the grille. I got the schematics for the HVAC system from Alldata and according to the diagram, when you press the AC request button the the HVAC controls it goes through the relay and then to the PCM where a bunch of stuff happens from there. I grabbed a scanner and I requested AC on in the Active tests and it kicked on no problem so I assumed that the HVAC controls might be the problem. But again since it was end of summer I kinda put in on the back burner. Well 3 weeks ago I was at the junkyard and saw a 2003 Yukon sitting there and the AC controls were there. I grabbed it figure I can test it on mine and what do you know it I had ICE COLD AC for the past 3 weeks every single day. Until today when I was leaving lunch and was sitting in the car idling and the AC turned off and now the same shenanigans are happening with the flashing button. I grabbed my scanned again and AC request in the Active tests kicked it right back on. I was looking at the data and most of the temps showed about 80 degrees or so except for the "Outside Air Temp", that one was sitting at a cool 37 degrees the whole time. Im not sure where its getting that number from but its definitely 85 degrees today so im wondering if the system thinks its too cold to work? Also im not sure where its getting that reading from or what sensor? I dont want to pay 250+ for a new Dorman HVAC controls unless I know thats gonna be the issue but im kinda clueless at this point as to where to look.

SORRY FOR THE LONG FIRST POST BUT I DID ALL I COULD THINK TO DO BEFORE COMING HERE HAHA!!!

 

[TJ Baker]

Outside Air Temp", that one was sitting at a cool 37 degrees the whole time. Im not sure where its getting that number from

That's what you need to address right there. Check the wiring for the ambient air temperature sensor. That sensor is typically in the front grille somewhere forward of the radiator and condenser. The sensor is wired to the HVAC control module. There is likely a poor connection somewhere in that circuit. Schematics should show any harness connector involved.

 

[Nemesis1990]

That's what you need to address right there. Check the wiring for the ambient air temperature sensor. That sensor is typically in the front grille somewhere forward of the radiator and condenser. The sensor is wired to the HVAC control module. There is likely a poor connection somewhere in that circuit. Schematics should show any harness connector involved.

AC just started working and I checked the scanner and the outside temp was 75 degrees. I’ll see if I can diag that sensor later and start from there

 

[nonickatall]

Logically speaking, your air conditioning works when the compressor is switched on.

The compressor engages when the conditions are met that the low pressure and high pressure switches are delivering the correct values, ensuring the system is properly charged. When you then activate the control unit and switch on the air conditioning, the control unit engages the compressor's magnetic clutch via a relay. That's the whole process.

If the compressor keeps switching off, the problem could be either in the circuit between the relay and the magnetic clutch, or between the control unit and the relay, because the control unit, for whatever reason, isn't attempting to engage the compressor or isn't engaging it properly.

To determine which end of these two possibilities to investigate further, simply connect a multimeter, or better a simple bulb, to the control wire at the terminal where the air conditioning relay is located. Then drive the truck, switch on the air conditioning, and observe whether the multimeter oder the bulb showing that the control engage the magnetisch clutch.

If it does, you'll see that the control unit is switching the relay, but the problem lies somewhere in the circuit to the compressor. Or if your bulb is flickering, then you know your controller is constantly switching on and off, which is of course strange, since you replaced it.

But anyway this way, you can narrow it down.

Good luck

 

[nonickatall]

That's what you need to address right there. Check the wiring for the ambient air temperature sensor. That sensor is typically in the front grille somewhere forward of the radiator and condenser. The sensor is wired to the HVAC control module. There is likely a poor connection somewhere in that circuit. Schematics should show any harness connector involved.

That shouldn't affect the compressor; even if the temperature sensor displays incorrect values, the climate control unit would engage the magnetic clutch, because the air conditioning system is already used to remove condensation. The compressor essentially runs as long as the conditions are met, and these are primarily the low-pressure and high-pressure switches...

If I read correctly, they have already been replaced, and I assume the cables were checked for loose connections and breaks.

 

[swathdiver]

The three flashes of the indicator lamp are telling you that the compressor is unavailable. The temperature has to be over 40 degrees for the compressor to run.

If your temperature sensor is fine, your symptom is indicative of low refrigerant.