AC clutch doesn't engage - Chevy Impala SS Forum
 
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post #1 of 8 (permalink) Old 06-19-2019, 11:15 PM Thread Starter
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AC clutch doesn't engage

Got a 96 RMW with climate control. My AC compressor hasn't engaged in like 10yrs. Blower works great all controls work properly, relay clicks. I need to replace Opti now so I figure I should fix this too. Is there any test to do before I just take the compressor out. Unfortunately car doesn't start but does crank.
Anything I can think is this happened about the same time I deleted the air pump, which I wouldn't think would be related.
Any help would be appreciated.
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post #2 of 8 (permalink) Old 06-20-2019, 07:34 AM
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I wouldn't just go throwing parts at it in an attempt to fix it - you'll end up not fixing the problem, spending a lot of money and getting very frustrated.

Let's see if we can get to the root cause of the problem and then address what needs to be done. There are a few things that need to happen for the compressor to engage.

First, you'll need the engine to be running, so once you get that far, we can continue with how the A/C system works...

The HVAC unit on the dash tells the PCM that it wants air conditioning by sending 12v out through the green wire with a white stripe.
This 12v signal goes through the Low Side cycling switch on the accumulator to the PCM.
Once the PCM sees this signal it says "OK, I'll ground the relay to engage the compressor clutch"

The most likely scenario, since you mention that it hasn't worked in 10 years, is that it's low on refrigerant. If there's not enough pressure on the low side cycling switch to close it, the PCM never sees the signal, therefore never grounds the coil on the relay, therefore never powers the compressor clutch, therefore never engages the compressor, etc.

Easy way to test this is to pull the connector off the low side cycling switch and take a paper clip and short the two wires together. If the clutch engages, go find the leak, fix it, get the system recharged and you'll be good to go. Just do this as a troubleshooting step - don't leave the clutch engaged for more than a few seconds.

If the clutch does not engage (remember the engine will need to be running), then we can go through a few more troubleshooting steps.
- Is there 12v at the low side switch?
- Is the 10A Prifan fuse good in the under hood electrical center?
- Is there power to this fuse when the key is on?
- Is the A/C Clutch Relay functioning/clicking?
- Is there 12v at the A/C Clutch Connector?
- Is there ground at the A/C Clutch Connector?

If the compressor clutch won't engage, it's a very low chance that the compressor itself is bad.

Check it out, and if what I explained above is confusing, please say so and we'll help you through it, step by step.

Good Luck!


Last edited by Fix Until Broke; 06-20-2019 at 09:47 AM.
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post #3 of 8 (permalink) Old 06-20-2019, 08:37 AM
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Thanks Fix-

I read up on this 'no-start' issue a bit this morning as I'm having to throw in a can every month due to apparent leak. I understand doing that too many times can fubar the overall system, so need to root cause for real repair.


Well back to this thread. I already figured whatever issue the OP's A/C had a decade ago is likely not the same one he's facing now. Before searching, I was just going to list the top 10 suspects - which you did well. But -



But, and I'm not saying I've NEVER done this to check compressor/clutch function, but I did read that it's NEVER advisable to jumper the low switch as it's there to protect from damage from 'dry fire' - which after a decade without even running I would suspect has no seal anymore hence ZERO charge. I guess the workaround MIGHT be to push the Schrieder and see if a good charge, THEN proceed at risk? Anyway, just tryna keep matters from getting worse for the OP than it sounds like they already are.


EDIT: And last but not least there's something about getting freon in by KOIO and forcing the fans, - but I can't imagine any useful diagnosis can come without the car running? It IS possible to run the car without installing the WP, but not alot of time available for diagnosis without it.

\'96SS SOB: SSRI, Herter Tune, Tri-Y II, , 3000 Edge, F/HO bars, METCO extendeds with CV MMC, Bilsteins, currently Vredestein Ultrac Sessanta (315/35 rear)
\'96FWB BUW-Butt Ugly White: PCMPerformance tune, HDFA w/ swissed filter, 1/2 SLP s.s. catback with H- and Flow Super 50s, oem opti rebuilt 3 times, SS Bars, METCO LCA, Airlift 1000, Monroe SS, PowerTrax No-Slip, CTS wheels with +1 rubber. Finally, wait for it... LT-4 knock module!

Last edited by 96 Black; 06-20-2019 at 08:43 AM.
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post #4 of 8 (permalink) Old 06-20-2019, 09:53 AM
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96 Black is correct - I edited my post above to say not to engage the compressor for more than a few seconds.

If there's no refrigerant charge in the system, then there will be low/no load on the compressor so very low/almost zero risk of damaging anything. Any oil that was in the system is still there so the compressor should be properly lubricated - the refrigerant does not provide any meaningful lubrication, it's thinner than water.

I can't think of any reason that adding a can of refrigerant when necessary would cause any harm (other than the environmental risks, depending on your beliefs ).
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post #5 of 8 (permalink) Old 06-20-2019, 11:17 AM
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I got "gently" reamed for doing that as the rationale is a small amount of 'atmosphere' with moisture and contaminants enters the system with each DIY freon top-off, plus risk of excess oil IF it happens to be included (even unlisted) in a given brand's can. I WAS doing this for several years when the leak required only 1 1/2 cans every 3-4 months, which calculated to 2x/yr. for the garage queen's driving season. At current rate of 1 can/mo. it's time for real repair.

\'96SS SOB: SSRI, Herter Tune, Tri-Y II, , 3000 Edge, F/HO bars, METCO extendeds with CV MMC, Bilsteins, currently Vredestein Ultrac Sessanta (315/35 rear)
\'96FWB BUW-Butt Ugly White: PCMPerformance tune, HDFA w/ swissed filter, 1/2 SLP s.s. catback with H- and Flow Super 50s, oem opti rebuilt 3 times, SS Bars, METCO LCA, Airlift 1000, Monroe SS, PowerTrax No-Slip, CTS wheels with +1 rubber. Finally, wait for it... LT-4 knock module!
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post #6 of 8 (permalink) Old 06-20-2019, 12:47 PM
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If you have a closed system that's never been opened but the charge has leaked out...

If you are charging via something like the Harbor Freight dual gauges kit, just purge the lines for a second with the refrigerant and then charge the system, it'll be fine.

If you open the system, best to vacuum it down. There are ways to "flush" it without vacuuming it but as to how well they work, I can't vouch for that.

"The unexamined life is not worth living." - Socrates
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post #7 of 8 (permalink) Old 06-20-2019, 01:37 PM
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Quote:
I got "gently" reamed for doing that as the rationale is a small amount of 'atmosphere' with moisture and contaminants enters the system with each DIY freon top-off, plus risk of excess oil IF it happens to be included (even unlisted) in a given brand's can. I WAS doing this for several years when the leak required only 1 1/2 cans every 3-4 months, which calculated to 2x/yr. for the garage queen's driving season. At current rate of 1 can/mo. it's time for real repair.
96 Black


I had always thought the reason for fixing the A/C instead of repeated filling had to do with oil loss. My understanding is that the oil migrates around the system with the freon and leaks out with the freon. The problem is how much oil is lost? It seems like a lot of work to find how much oil is still in the system and add it back in. This would be less of a worry if the freon was lost when the A/C was not being used.

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post #8 of 8 (permalink) Old 06-21-2019, 08:18 AM
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Quote:
Originally Posted by Z09B4U View Post
I had always thought the reason for fixing the A/C instead of repeated filling had to do with oil loss.
Or you just get tired of refilling it. It also depends on where the leak is. I once fixed a car that had gotten a stick rammed into the very bottom of the condenser. All of the oil eventually leaked out of that hole since it was at the very bottom of the system, compressor ran dry, and that was the end of that. Leaks at the top of the system (like leaking test ports, see that ALL THE TIME) don't typically lose oil, just refrigerant.

"The unexamined life is not worth living." - Socrates
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