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Low side pressure drops when compressor runs.

egsorr on Sun September 02, 2007 7:15 PM User is offline

Year: 99
Make: Cadillac
Model: Deville
Engine Size: Nrhtstar
Refrigerant Type: R134
Ambient Temp: 90
Pressure Low: 40
Pressure High: ?
Country of Origin: United States

My 99 Cadillac gave an ACM code for low refrigerant and the compressor stopped completely. I previously had a wiring problem on the low pressure sensor and checked it first.
I cleared the ACM code and the AC started to cycle off and on.

So I picked up a can of refrigerant with a gauge at the parts store.

When the refrig hose is connected to the low side valve it showed about 32psi when the compressor did not run and drops to about 5psi when the compressor kicks on.
I jumper across the pressure sensor and the compressor runs continuous and the pressure reads about 5psi. No cooling.
Remove the jumper and it cycles off and on pressure up and down.
I tried a couple of squirts of the refrigerant, and brought the pressure up to about 40psi. No change, still goes up and down with on and off.

Did I screw up shooting that stuff into my system?

Why do I believe the dealer will call it a bad compressor for $1000.00, regardless.
Scared to take to just anybody since I had an AC shop blew my compressor once and not own up to it. ( shot freeze 12 into my R12 with out testing high side and or vacuuming, I believe this was the cause).

Don't trust dealer and scared of unqualified techs who claim to do AC.

What would I expect this kind of problem to be?

Who should I trust?


Chick on Sun September 02, 2007 7:33 PM User is offlineView users profile

First you need to find and fix your leak. Adding refrigerant with the low side only can ruin the system..Didn't you say yopu suspect that in the last failure?? If you are going to do the repairs yourself, you will need the Mastercool AC repair handbook and also the DIY'er starter kit with the high and low pressure guages..Once you have these the repair will become much easier.. With UV dye in the system, look for leaks around the clutch (front seal leak) and all fittings..Hope this helps..
PS: If you don't want to to do this yeourself properly, stop and find a shop qualified to find and fix leaks, you risk ruining an expensive system otherwise...

-------------------------
Chick
Email: Chick

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Freedoms just another word for nothing left to lose

egsorr on Mon September 03, 2007 10:40 AM User is offline

First, thank you I really appreciate the reply.

This car never had a leak. The previous problem was a rat chewed through the sensor wire before.

This would be the first time I ever had an issue with the "system" other than that.
My old Riviera was the one that was messed up with freeze 12, and no high side connections.
I hope I have not hurt this one by shooting in a couple pounds of the over the counter stuff.

So the symptom of seeing what appears to be good pressure when the compressor is not running and seeing it drop to near nothing when the compressor runs means I have no pressure? I had read something about equal pressure on the high and low side when the system is not running. Is that what I am seeing?

So the pressure when the compressor is running is the actual pressure? I must have a pretty serious leak then huh?

I think this is probably something I should have a professional look at. I may not be the best suited at doing this one myself. Really need to get the 99 cadi off the ground to see the compressor. Starting with the book sounds like a really good idea though! Thanks!

chris142 on Mon September 03, 2007 12:09 PM User is offline

Quote
Originally posted by: egsorr




This car never had a leak. It does now. If it has Dye ck the compressor and it's seals on the back where the manifold goes.

mk378 on Mon September 03, 2007 12:09 PM User is offline

The low side pressure should be much higher than 40 "static" (after pressures have equalized because compressor has not run for several minutes). Based on what you're seeing, it appears that nearly all the refrigerant is gone. It would be good to confirm that with a high side reading but right now I think you should start looking for leaks before considering a recharge

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