5

2007 Escalade AWD.

Yesterday, I noticed that the air conditioning keeps turning on and off.

To clarify: the control unit does not indicate that it's turning off. I still have the fancy snowflake icon, temp set to desired level, etc.

Air will blow cold for a few seconds, then warmer, then cold, and so on. After the car has been running for awhile it seems that the period of on/off increases, but it never gets back to 100% on.

We're in Dallas, and I can tell you that global warming is real. Temps are well over 100° (F) lately.

This happens if the car is stopped (idling at a light), moving, or whatever. There appears to be no correlation between vehicle speed and AC functionality.

The car is not overheating.

Oil was changed by a local shop about a week ago, otherwise no recent service.

I'm going to put some UV dye in the system and look for leaks, but I'd be surprised if one randomly appeared. It feels more like the compressor is periodically engaging / disengaging, and I'm not sure what would cause that to start out of the blue.

Thoughts?

4
  • Identify the AC compressor clutch relay location and type and try replacing it.
    – Al_
    Jul 24 '18 at 9:35
  • 1
    Have you a possibility to measure the output of the pressure switch while the AC is cycling? A cycling AC is a textbook symptom for a over-pressure issue (or defective sensor)
    – Martin
    Jul 24 '18 at 11:11
  • @Myself my oscilloscope is dead. I’ll see what else I can McGyver together. I don’t see how it could be over pressurized unless someone snuck into the garage and added refrigerant. ??
    – 3Dave
    Jul 24 '18 at 14:18
  • Except from overfilling an overpressure signal can be generated by an defective expansion valve or a defective pressure sensor/switch
    – Martin
    Jul 24 '18 at 20:27
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First you should get a service for your AC. All AC´s more or less slowly leak coolant gas. If it has last been serviced 2 or 3 years ago, chances are you are simply running low on coolant. If there is too little gas in the system, it either shuts off - or it can even get damaged.

If, after a refill of your AC, the Problems prevail, check the AC compressor clutch relay (as @Al_ mentioned) and the clutch itself, in that order.

3
  • You're wrong about the primitive ones. In fact the more advanced ones (systems with variable displacement pumps, especially if clutchless) are more likely to be damaged since they lack a low pressure side switch/sensor (such a sensor has no purpose in a system which is able to control the suction pressure) and as such can run with very low charge levels which can seriously deprive the compressor of adequate lubrication. And, anyway, too frequent cycling can be very damaging to the clutch assembly and shaft seal, due to the heat buildup caused by the engagement phase slipping.
    – Al_
    Jul 24 '18 at 11:49
  • Clutchless compressors are in fact able to run with no charge at all (the pressure transducer of a clutch equipped VDC is still able to cut power to the clutch coil off if the charge level lowers too much). This can seriously damage the compressor since, in that case, any lubrication comes only from the oil inside the compressor and therefore it can heat up very quickly.
    – Al_
    Jul 24 '18 at 11:51
  • 1
    @Al_ Thank´s for the clarification - i guess primitve was a bad word choice. Edited it. Just make sure your system is filled properly, first :)
    – Daniel
    Jul 24 '18 at 11:52
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Since this was asked three years ago, my guess is either a problem occurred in the hvac controls or a leak occurred from normal war and tear. Industry guidelines use several grams of refrigerant leakage per year as the maximum for a sealed system. 28.3 grams per ounce. GM uses either a combination low/high pressure sensor (two wire type) or transducer (three wire type) to sense lower than ideal standby pressure on the discharge side or excessively high pressures, signaling the ecm to disable power to the compressor clutch coil. Standby pressures are around 70-90 psi in summer temps. High side operating pressures are between 1250-250+ psi. When a leak occurs, refrigerant, oil and dye are released with dye and oil marking the leak site.

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