Automotive Air Conditioning Information Forum (Archives)

spinetx on Thu July 24, 2014 3:03 PM

Year: 2001
Make: gmc
Model: yukon
Engine Size: 6.0
Refrigerant Type: 134a
Ambient Temp: 95

My 2001 gmc yukon with rear air won't blow cold (front and rear is warm). When I have the AC on the clutch will cycle on and off every 15 seconds or so. I don't have seperate high and low gauges all I have is the gauge that comes with the refrigerant. When the clutch cycles "on" the pressure goes up to 50 psi+/-
when it cycles "off" the pressure bleeds off to 20+/-. This repeats itself and the air never gets cold.
When I check the pressure with the AC off the pressure is at 350. I added about 10 psi of refrigerant just to see if it made a difference and it did not change. Any ideas on this would be greatly appreciated.

HECAT on Thu July 24, 2014 4:42 PM

The numbers you have provided don't make sense. Suggest a vacuum and recharge to spec by weight.

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HECAT: www.hecatinc.com You support the Forum when you consider www.ackits.com for your a/c parts.

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AC_Doc on Thu July 24, 2014 6:17 PM

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Sometimes you must accept things at faith value!

AC_Doc on Thu July 24, 2014 6:29 PM

You have the pressure vs clutch action backwards.

1) When the clutch cycles "ON" the compressor draws refrigerant out of the cab evaporator and the pressure goes DOWN until it reaches a set pressure of 20 psi and the clutch disengages. The pressure will the increase due to the heat load in the cab until the pressure is 50 psi at which point the clutch re-engages and the sequence starts over.

2) The drop from 50psi to 20psi when the clutch engages and the compressor pumps is because there is way insufficient refrigerant to meet the needs of the system. Since you say "no cooling" the system may be empty and only be pumping air.

3) In any case, most or all of the refrigerant has leaked out. Replenishing the refrigerant will only delay the inevitable by a week, or maybe a day.

4) Time to have the system leak found and repaired, the air pumped out, and the system charged to specifications.

Are you prepared to do the work yourself?

AC_DOC

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Sometimes you must accept things at faith value!

spinetx on Thu July 24, 2014 6:29 PM

Sorry, the last pressure I gave was in kPa (350) it was 50-55PSI.

spinetx on Thu July 24, 2014 8:18 PM

If it was something simple like replacing a switch or just replenishing some refrigerant I would do it myself. But I will take it down and have it flushed and fixed/refilled.

spinetx on Fri July 25, 2014 11:16 AM

OK it was definitely low on refrigerant. I jumped the clutch switch long enough to keep the compressor going and it took 2 cans. Plugged the switch bak in and it wrked fine. So now I will take it in to the professionals and have the leak fixed and recharged.

Cussboy on Fri July 25, 2014 2:27 PM

Quote
Originally posted by: spinetx
OK it was definitely low on refrigerant. I jumped the clutch switch long enough to keep the compressor going and it took 2 cans. Plugged the switch bak in and it wrked fine. So now I will take it in to the professionals and have the leak fixed and recharged.

Congratulations. Many new posters here think that adding refrigerant to a leaky system is a fix, then two leaks later they're low again. So congrats on doing the right plan.