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#1
08-20-2014, 08:46 PM
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No power to AC Relay, need help!
Hey everyone,
I have a 1998 Pontiac Grand Prix GTP and the AC just stopped working. The fan blows but i dont get any cold air. I have noticed the AC clutch plate does not move and the relay does not click when the ac is toggled. Long story short, I think I need a wiring diagram for the AC. Here is what I have checked/ruled out so far. 1. When I toggle the AC, the AC clutch relay does not click so i assume there is no power getting to the relay. (I have recently had other wiring issues so I'm guessing its the same case) 2. I swapped the AC clutch relay with the fog lap relay (they are the exact same relay) and the fog laps still worked so i know its not the relay. 3. I have checked the AC fuse and that is fine. Any thoughts or help would be greatly appreciated? Thanks everyone, Steve 
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#2
08-20-2014, 09:22 PM
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Re: No power to AC Relay, need help!
Kind of need a scan tool to read PCM data, for diagnosis.....
Looking for three things: One, check for an AC trouble code..... Second is AC request from the control head...... Third is data from the pressure sensor......this will tell you if you have enough refrigerant in the system for the compressor to start..... If you don't have access to a scan tool, then get a set of gauges to check pressure in the system....if too low, the PCM will not ground the clutch relay..... Pressure in the system, on a cold vehicle, with the engine not running, should be close to ambient temp.......so if the air temp is 80 F, pressure should be around 80 psi.......if pressure is 40 psi or less, the PCM will not ground the relay.....
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#3
08-21-2014, 07:38 AM
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Re: No power to AC Relay, need help!
Number one cause of mobile a/c failure is loss of refrigerant due to a leak. You need 47 psi in system to activate compressor-- do you have that?
play the odds 65% I see have lost refrigerant
__________________
Automotive A/C Engineer with: '99 IH 4700 Toy Hauler (2) '95 GEO Prizms both maroon '99 GMC Yukon '95 Chev 3500, 454 Dually Crew Cab- 145k miles- Wife's Camel trailer puller. '94 Astro- 370k miles '94 Firebird Formula- 5.7L 180k miles- gone- '92 Chevy Lumina Van 3.8L 264k '86 GMC S-15 - 2.8L 154k '87 Buick Park Ave . 187k '86 Buick Park Ave 3.8L 199k miles- gone '77 Chevy Vega- 2.5L 175k miles gone but not forgotten '68 Camaro 396 4 spd RS/SS -72k miles-
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#4
08-21-2014, 09:27 AM
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Re: No power to AC Relay, need help!
I hooked up a scan tool that I have and did not find any codes. Granted the tool i have is a cheaper ($100) scan tool from harbor freight so I'm not sure it would pick up stuff from the PCM. I think it only reads codes when the check engine light is on.
I'll figure out a way to read the PSI and get back to everyone. Thanks for the help thus far everyone!
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