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Intermittant AC

Jcol on Mon June 21, 2010 9:58 AM User is offline

Year: 2002
Make: GMC
Model: 2500HD
Engine Size: 6L
Refrigerant Type: 134A
Country of Origin: Canada

Hello - I posted this over at the GM truck forum and someone suggested I should post here. I'm in southern Ontario so I only use the AC for about 4 months out of the year. Last August before going out on a trip I noticed that my AC would stop working while driving in to stop and go traffic . The AC would always start from cold but soon stop cycling. The AC would run all day if I was going down the highway, but as soon as I stopped, say to refuel it would not start again. I discovered that if I left the AC off for about 30 minutes and continue on it might start up again and be OK. Thinking it might be low I bought a can of 134 with a gauge, however in my driveway with the truck idling and the AC on the pressure was right in the middle of the "green" zone on the guage so I did not add any refrigerant. A few days later my AC stopped working as I was pulling into my driveway. Leaving the truck running, AC on but not cycling I put the can on and the low side read 75 psi which was in the red zone of the guage. It seemed that pressure is building in the system and that is why it stops cycling. At this point I took the truck to the place I get it serviced. This is a modern garage with a good rep. They checked my system, removed flushed and recharged the system. Saw the pressure start to build on the low side and started to focus on my fan clutch and the condenser which they cleaned. A new fan clutch was installed. They say the I wasn't getting enough air flow through the condenser to cool the hot gas and this is why the pressure was building. This was September of last year and it seemed to solve the problem, however it never got really warm again so it might just never have been tested. Now as the warm weather has started the symptoms have returned. As soon as we get above 80 F the AC will stop cycling if the truck stops and I see 75 psi on the low side. I plan to take it back to the same shop however I don't expect they will believe that they never solved the problem but I'd like to have some more ideas. Seems to me the condenser might be the suspect?? Thanks.

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2002 GMC 2500HD

HECAT on Mon June 21, 2010 10:10 AM User is offline

Throw away the tire gauge. Low side pressure will rise (equalize) when system is not running. High side will rise with poor air flow (clean condenser and replace fan is good). Sounds like a clutch gap issue to me.

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HVargas on Mon June 21, 2010 12:26 PM User is offlineView users profile

Without real pressure readings it is very hard to diagnose anything with the A/C system. Seems like they are doing a lot of flushing. What was the reason for the parts replacement in the first place and what was all replaced?

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mk378 on Mon June 21, 2010 2:09 PM User is offline

The first thing to do here is observe whether or not the compressor is staying engaged when it is not cooling. If the compressor is not engaging when it should, it's very often the clutch gap.

Jcol on Mon June 21, 2010 3:34 PM User is offline



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2002 GMC 2500HD

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