Automotive Air Conditioning Information Forum (Archives)

trx680 on Mon June 04, 2012 7:48 PM

Year: 2001
Make: GMC
Model: Sierra
Refrigerant Type: 134

My A/C in my 2001 GMC Sierra hasnt been cooling. I know nothing about A/C's so I took a shot at it and bought one of those recharge systems with the freon can and gauge. I hooked it up and noticed the gauge was getting high (in the red) then the compressor was kicking off and the pressure would drop low and the compressor would come back on. It would cycle like this about every 10 seconds.

Any idea why it cycling like this?


thanks !!!

GM Tech on Mon June 04, 2012 9:01 PM

Does it cool driving 50+ mph? My guess is that you have high pressure cut-outs due to little or no air across condenser due to worn out clutch fan (radiator fan)....does cycling stop when you spray condenser (in front of radiator) with a garden hose?

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

buickwagon on Mon June 04, 2012 10:27 PM

The kit you bought comes with a low-pressure gauge. The compressor should run, dropping the pressure to around 21 or 22 psi. At that point, the evaporator would freeze over, so the compressor cuts out. The pressure rises to ~40 psi before the compressor kicks back in again.

So, is there any chance you are mistaking kick-off for kick-on? When the compressor is running, the centre will be spinning. When it kicks off, the clutch releases and the centre stops spinning.

Oh, and by the way, you are playing russian roulette with your system. Over-charging or under-charging can lead to damage. You cannot determine the proper charge by pressure, only by weight.

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I've saved hundreds on service by spending thousands on tools.

mk378 on Mon June 04, 2012 11:02 PM

You need to measure both pressures (high and low side) to know what is going on. The single gauge only looks at the low side.

Edited: Mon June 04, 2012 at 11:04 PM by mk378

bueller on Tue June 05, 2012 6:11 PM

You could also have air in the system. Even the smallest amount of air can cause the symptoms you're describing.