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A/C Clutch Not Cycling On; A/C Relay Removal
Topic Started: Oct 23 2017, 04:07 PM (397 Views)
julio3231
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Hey guys,

I scraped the surface of A/C diagnostics on my 91 vert over the weekend. I added R134a fittings to charge the system and added some refrigerant. Low side pressure came up and seems to be holding, but the clutch is not cycling.

From there I checked the wire that goes to the clutch for power with the blower fan on and A/C button depressed (A/C) button does light up. I am not showing any voltage going to the clutch via connector behind headlight. If I'm not mistaken I should see 12 volts here, correct?

Next, I tried to remove an A/C relay and realized I might break it while trying to pull it. Do these relays often fail? I'm thinking it might be worth it to buy two new ones that should be known good parts, but id like to salvage the ones I am removing if at all possible.
Any tips tricks to get those removed would be helpful.
Edited by julio3231, Oct 24 2017, 12:49 PM.
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bkgeig
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The 1994 factory service manual posted in that section has detailed info for chasing down electrical gremlins in the AC wiring. I believe the AC elec didn't change between 1991 and 1994. Basically you want to work your way through the wiring either from the compressor back or from the AC switch forward, or a combination of the two. I've had to do this several times on my '93 and never had to remove the relay. I think you can back probe it to test if need be. If I had to take a guess, I would look at the temp sensor at the throttle body. If you ground that wire to the body and the AC works, you know you've got a bad sensor.
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geogonfa
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:gp
That temp sensor is a single spade sensor located in the right side of the lower Intake manifold below the Throttle position sensor and above the Alternator (Manifold Temperature Sensor)

http://geometroforum.com/topic/5044844/1/#new

08A-064 ELECTRICAL DIAGNOSIS HVAC COMPRESSOR CONTROL


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julio3231
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i will try this when I get home.
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julio3231
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After bleeding what must've been a tiny bubble out of the cooling system, I hooked up the r134a can and gave it a little charge. The compressor kicked on and i didn't get cold air, but at least I can rule out the compressor/clutch/ wiring hopefully at this point.

I have never tried to diagnose A/C without an A/C diagnostic machine. I cant see the high side or pull a vacuum. I was hoping I could just switch out the fittings and give it a charge and have it all work out.

I'm starting to think i should just have a shop look at it. Recover the system pull vacuum. Add esther oil and charge with R134a. I dont have the right tools to do it.
Edited by julio3231, Oct 25 2017, 12:33 AM.
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MR1 Kingsbury
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Exp. builder/rebuilder

julio3231
Oct 25 2017, 12:25 AM
After bleeding what must've been a tiny bubble out of the cooling system, I hooked up the r134a can and gave it a little charge. The compressor kicked on and i didn't get cold air, but at least I can rule out the compressor/clutch/ wiring hopefully at this point.

I have never tried to diagnose A/C without an A/C diagnostic machine. I cant see the high side or pull a vacuum. I was hoping I could just switch out the fittings and give it a charge and have it all work out.

I'm starting to think i should just have a shop look at it. Recover the system pull vacuum. Add esther oil and charge with R134a. I dont have the right tools to do it.
correct....You do not have the right tools if you cannot evacuate the A/C lines... when you put on new fittings, did the system become open to atmosphere? if so, then you must evacuate to recharge.

Also, the 134a does not agree with original orings. all oring connections should be opened and replaced with 'green' orings. then evacuated, then oiled and charged.
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julio3231
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I thought it was the PAG oil that didn't like the o-rings? That's why I wanted ester oil put in instead (Retrofit oil) and maybe some dye.

The A/C System was empty when I took out the old valve cores from the R12 fittings which leads me to believe there is probably a leak in the system. I have a set of green o rings, a TXV valve and a new dryer. I was hoping to only have to repair what failed though as it is an old car and some of the A/C lines don't look like they're going to be fun to try cracking open. Now I have refrigerant in the system, so I might at least be able to monitor how bad the leak is.
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geogonfa
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Just my .02ยข...There are alternatives to 134a that don't require evacuating the system...but changing all the seals is reccommended

https://www.amazon.com/Enviro-Safe-R134a-Refrigerant-Dye-Cans/dp/B01DPSPTZO/ref=sr_1_sc_1?ie=UTF8&qid=1508950052&sr=8-1-spell&keywords=evirosafe

...suggest reading post #67 @ http://geometroforum.com/topic/8111407/5/#new

also suggest maybe renting a gauge set from a parts house or getting a set from harbor freight...

https://www.harborfreight.com/ac-r134a-manifold-gauge-set-62707.html
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julio3231
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That post 67 is very helpful. Maybe I should make a weekend project out of replacing o-rings, and then try charging with Envirosafe from atmosphere which is what it is designed for. I had never heard of it before. Very interesting. That could save me some money.

I guess the only alternative would be replacing o-rings and having an auto shop charge it.

Either way it sounds like I should replace the o-rings to be sure there's no slow leak by the time refrigerant is reintroduced to the system. I just hope the lines want to come apart easily enough. I haven't broken anything yet. Knock on wood.
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