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Search Auto Parts Search 98 GMC 110 psi at low pressure port - no cold air Sign up here!   Email This Post Auto Repair Home>> Automotive Repair>> AC Auto Repair Help Forum Big Blue New User Feb 27, 2006, 3:57 PM Post #1 of 4 (2688 views) 98 GMC 110 psi at low pressure port - no cold air Sign In Recently the A/C unit stopped putting out cold air. The pressure at the low-pressure port is high (~110psi). Also, I don't hear any kind of engagement when I turn the A/C on – however being a diesel it is kind of loud. It’s hot here in Kona, Hawaii. Please help. Tom Greenleaf Ultimate Carjunky / Moderator Feb 28, 2006, 8:58 AM Post #2 of 4 (2678 views) Re: 98 GMC 110 psi at low pressure port - no cold air Sign In If the outer hub of the compressor doesn't click on and pump it's just like the A/C is turned off. It could be a low pressure switch that has failed and some testing is required. You can jump that switch with a wire but I would test it for 12V or so on one side first. That should force compressor to come on. If no power to that switch you need to check or replace the relay and the fuse. 110 low pressure is enough to trigger the switch. They are made to cut out at about 25 psi. That low pressure switch can be replaced if bad without messing with the refrigerant. Diesel or not the A/C works the same. This may only be a simple job and if I or anyone uses names of parts that you don't know just ask. Don't mess with three wire switches right now. Aloha, T I lived on Ala Moana Blvd for a while in the 70s (Honolulu) Big Blue New User Mar 1, 2006, 3:10 PM Post #3 of 4 (2663 views) Re: 98 GMC 110 psi at low pressure port - no cold air Sign In Tom, thanks for your reply. I'm glad to hear that you got to do some time in the islands. With the A/C on high: I tested the wire to the low pressure switch and got ~13V. I jumped the low pressure switch wire and the compressor did not turn on. I tested the wire to the compressor with the low pressure switch jumped, and didn't get a reading. Is there a relay or something between the low pressure switch and the compressor that I can test and/or replace. Just a note, I tried switching the starter relay and the A/C relay (they seemed to be the same) and nothing changed. Tom Greenleaf Ultimate Carjunky / Moderator Mar 1, 2006, 6:00 PM Post #4 of 4 (2662 views) Re: 98 GMC 110 psi at low pressure port - no cold air Sign In If you had power at the low switch and the compressor's clutch didn't kick in it may just be a matter of adjusting the clutch gap. Check to see if power gets to the clutch. You can also just tap on it but be careful it may start right up. If so and warm out it will stay on if the refrgerant charge is right. It almost certainly takes a puller to get the clutch off to adjust it and I'd have to see it to know just what to do for that. This does not sound like a relay but if there's no power when jumped low switch it could be. It would help if that works to check the pressures while compressor is running, at about 1,500 rpm - doors open and A/C on full blast. If you get nice cool air and a non cycling compressor the clutch gap is near a certainty of the problem. Feel free to hit a site that is just A/C if things are not working out and some sharp tacks are there to help at HTTP://www.AutoACsystems.com -- we are coopertive friendly sites and either will do our best to get you going. If you go there just click on the "Cool Zone" and post all the history you have will speed things up, T   Email This Post   Automotive Repair     Auto Body Repair and Refinishing     Heating or AC Issues     Electrical and Wiring     Brake Systems     Car Stereo Repair Advice     General Discussions     Car Making Funny Noises     Engine Fault Codes     Engine Troubles     Exhaust Systems     Steering and Suspension     Transmission Troubles     Tricks of the Trade Automotive World     General Discussions     Antique Car Talk     Car Shows and Events     The Bargin Bin     Motor Vehicle Inspection     Car Care Tips     Traffic Tickets     Gasoline, Motor Oils, Concept Cars and Engines     Auto Insurance, Financing, Leases, Warranties Truck Repair     General Discussions     Truck Engine Repair     Truck Suspension Repair Motorcycle Repair     General Discussions     Motorcycle Engine Repair CarJunky     Open Posting     Board FAQ's     New Board Suggestions

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