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RWESS
New User

Jun 5, 2005, 7:29 PM

Post #1 of 4 (2790 views)
Air conditioner Sign In

This is my first visit to this forum! I am an ASE certified heavy duty truck mechanic with a question about my A/C Clutch that won't engage at all on my 1991 GMC Siera 2500 2WD. There is an A/C icon that flashes on the heater display about ten or fifteen times then it stops flashing until I push the A/C button again. The last time it did this it seems like all I needed to do was add refrigerant. The system has pressure in it, about 80 or 90 psi. I suspect a the low pressure switch on the accumulator may have failed but I am not too familiar with the circuit for the clutch on this model. I need help through this or advice on where to get diagnostic help. I looked at the fuse for the A/C and it was OK, other than that I have not tested a thing. The flashing A/C light has me concerned that there may be some extra built in diagnostics. Thanks for your attention and replies, RWESS


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Jun 6, 2005, 4:04 AM

Post #2 of 4 (2785 views)
Re: Air conditioner Sign In

Check for power (voltage) at the low pressure switch. It will cut out at about 25 psig. It can be jumped (just unplug and use wire or what ever and compressor should engage) and take pressures, which are totally temperature dependant. If it's low on refrigerant more than a couple times you need to add oil! - and if too often need to fix the leak. Could use some more info here. Is this still R-12 or 134a? Do you have gauges? Hit back and we can fix this. Can buy gauges for $100 bucks or less and adaptors that will allow use on both R-12 or 134a - I don't deal with alternatives, Good luck - we are here to help,



RWESS
New User

Jun 6, 2005, 10:32 AM

Post #3 of 4 (2780 views)
Re: Air conditioner Sign In

 I own a White Industries 134A machine, I bought it used from the trucking company that was closing up in 1999. It is never too hard to find some one that has a broken air conditioner and we have some farm machinery that I converted to 134A too.
The system on the GMC was converted to 134A about 1999 and had worked pretty well but since I didn't relace all the hoses it will loose some charge over the course of a season. I was a little confused by the flashing light in the heater control area of the dash and kind of was in a hurry and not thinking that there ought to be enough charge in the system since the gauges read about 80 or 90 when I hooked the machine up. I will work my way through the circuit using my frail memory. There are some recent class 8 truck systems that have diagnostic circuits built in and I wanted to see if you or some one else knew if this truck had something like that. Thanks again for the reply. PS I share your disdain for the drop in replacements. Some of them are butane or propane based. Extremely dangerous when under pressure, in a collision or to an unsuspecting technician.


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Jun 6, 2005, 3:02 PM

Post #4 of 4 (2773 views)
Re: Air conditioner Sign In

Cool trick - go to a chain store and get a thermometer with the wired remote ( about 10 bucks or less) --they are fast and accurate -- can get output temps and ambient with the silly thing. It's far more handy than the meat thermometer type and faster. Great tool for adjusting A/C refrigerant. To be done carefully - over charge is NOT a good thing,







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