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Tool Talk Discussion Forum

OT-91 Buick A/C not operating

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jCarroll

07-04-2005 19:15:49




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Car is a '91 Buick Park Avenue. No A/C.
Compressor is not running.
Gage on suction line reads 100 psi (so I'm thinking it's not low on R-12).
If it has a low pressure switch, it should not be OPEN with pressure in the system.

Can I jump the compressor to see if it's the control panel switch? The compressor has a connector with a green and a black wire - which is ground, which is hot?

Ideas? Suggestions?

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gab

07-05-2005 18:59:32




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 Re: OT-91 Buick A/C not operating in reply to jCarroll, 07-04-2005 19:15:49  
The cycling switch on the accumulator and the compressor relay were problems on those cars. Unplug and jump the two switch wires, if that don"t work, swap the a/c relay with the horn relay. I think all or most of those relays behind the engine on the firewall are the same. Just swap with one of the same number, horn relay? Jim



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RusselAZ

07-05-2005 07:17:04




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 Re: OT-91 Buick A/C not operating in reply to jCarroll, 07-04-2005 19:15:49  
IF it has the automatic temp system you will need to be able to read any possible trouble codes. There are several that will shut the AC down and keep it down until they are cleared. A signal from the high pressure switch will and this signal could indicate the orfice is plugging. A signal from the low pressure switch will shut it down if it doesn't have enough freon to keep the pressure above a preset level while running. Another common code is for the engine cooling which will shut down the AC.

If it is a manual temp control system, codes won't shut it down.

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Revredneck

07-05-2005 04:51:58




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 Re: OT-91 Buick A/C not operating in reply to jCarroll, 07-04-2005 19:15:49  
Howdy,
You need to get hold of a wiring schematic for the system. I used to work on those cars, and sometimes a bad pressure switch could drive you crazy! Your problem is most likely a bad pressure switch mounted in the rear of the compressor. Some models had a pressure sensor (3 wires) that fed info to the computer. The compressor clutch coil is energized by a relay that is controlled by the engine computer. Those pressure switches could be either computer inputs or in-line cutouts designed to prevent operation in the event of too little or too much head pressure. I have been able to jump across the contacts in the switch wiring harness to get some of them going, but be sure that you know exactly what the switch does before you do that. If the switch is bad and needs to be replaced, you'll have to drain out the freon to do the job. So carefully decide if it's worth bypassing a safety switch to get cold air. Good Luck and God Bless, Tommy

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lucasss

07-05-2005 04:16:46




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 Re: OT-91 Buick A/C not operating in reply to jCarroll, 07-04-2005 19:15:49  
i agree to check for voltage at compressor. if not , you may want to get an a/c relay ,its a little square box in the fuse panel i think ,,and cheep.also check any fuse marked a/c . lucas



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Bob

07-04-2005 22:34:53




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 Re: OT-91 Buick A/C not operating in reply to jCarroll, 07-04-2005 19:15:49  
The clutch cycling switch on the low side often goes bad (does not make contact when it should). Pull the connector off of it, and use a little piece of wire to jumper the two terminals. If the clutch kicks in AND the system cools, you know the switch is bad. (If you were to keep operating it with the jumper wire in place, likely the evaporator would freeze up.)



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Jon Holt

07-04-2005 19:54:35




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 Re: OT-91 Buick A/C not operating in reply to jCarroll, 07-04-2005 19:15:49  
If you have a test light check for power down at the compressor. If no power then check at the cycling switch. If there is power there on one side but not on the other the switch could be bad. If not you will need to go in further.



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