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low and hi side @ 150, comp running

Squidward on Wed July 07, 2010 2:33 PM User is offlineView users profile

Year: 1999
Make: Chevy
Model: Malibu
Engine Size: 3.1
Refrigerant Type: 134
Ambient Temp: 95
Pressure Low: 150
Pressure High: 150
Country of Origin: United States

Just bought a 99 Malibu for my daughter. AC was not working, original owner (since it was new) said AC was never serviced. AC was not a deal breaker.

Anyways, checked pressures when we got home. Compressor clutch engages when ac turned on, and low side gauge was pegged (assuming 150+ or so), and hi side was at 150. I was amazed that the clutch was even engaged, and it was even occasionally cycling during the test drive although blowing warm. During the pressure check I made sure I had both high and low valves shut on the gauge manifold so that they weren't cross connected.

Would this be an indication of a faulty orifice tube not making a pressure drop? Compressor, perhaps? Pressure stayed very stable during the check, almost like the compressor was not running and it was just equalized static pressure in the system.

Thanks!



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"It ain't easy bein' cool..."

GM Tech on Wed July 07, 2010 4:53 PM User is offline

If your compressor was "cycling" it was off of high head pressure cut-outs---- since you have a V-5 variable stroke compressor that DOES NOT cycle by design....it destrokes---which may be the case as you present it....


But the most likely cause is a catastrophic loss of refrigerant to the point there is not enough to pump- nothing is changing to liquid- you have about 5 ounces in a 1.8 lb system---and you are basically reading static system pressures wit your gages. Shafte seals and body o-rings are primary leak locations--- I suggest you recover what ever is in your system- then evacuate, recharge and see if cooling comes back---then if so...use a good leak detector to determine your shaft seal is the culprit- also look for oily residue about the compressor body....

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Dougflas on Wed July 07, 2010 5:23 PM User is offline

Just a question...are your handwheels on your guages closed?

Squidward on Wed July 07, 2010 10:48 PM User is offlineView users profile

Thanks, GMT. I was unaware that it had the V5 and was anything other than a standard ccot system. I will do as you recommended.

BTW, any good reference info (links, etc.) that could explain V5 system operation so that I can rationalize the mechanical operation of this system? I am much more familiar with CCOT stuff from the 70's/80's and POA systems with fixed capacity compressors. I will do some searching of my own, too.

I did notice some oil residue down by the compressor and up into the wheel well, but since the oil filter on the 3.1L is right next to the ac compressor, I thought that maybe that was the source. I'll take a closer look now.

Thx!

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"It ain't easy bein' cool..."

Squidward on Wed July 14, 2010 4:15 AM User is offlineView users profile

Update:

Decided to replace the compressor since it sounded a little rough. Compressor was removed, and the OT pulled. The OT had some gunk on the screens and a dark smoky "soot" on the otherwise white plastic. The OT outlet screen also had a hole in it. It was enough to concern me, but it certainly didn't look anywhere close to the classic "black death" pics I've seen.

The evap and condenser were pressure flushed both front and back. Some debris and dirty oil came out. The OT was replaced. I drained and measured the oil in the new compressor, and then re-added to bring the system up to 9 oz. Accumulator was replaced last, and the system was evac'd and charged.

Here's the rub...

After getting about half the charge in, the pressures looked ok and the vents were blowing cool. Compressor was on continuous. Low was 50-55, and hi was 225-ish. I continued on charging to reach the factory spec of 28 oz. It was during the continued charging that the compressor clutch started cycling irregularly. When the clutch was engaged, pressures were 45-50 low, and 250-275 on the hi side. Max pressure of 315 was achieved during rev up to about 3k. Ambient was about 105F.

When the clutch was engaged and pressures were stabilizing to pretty normal values the clutch would drop out for 3-5 seconds. Low pressure would go up, hi side came down. Then the clutch would unpredictably come back in.

Could I be looking at an electrical issue, like the pressure switch at the condenser inlet? Maybe a compressor clutch relay dropping out?

Does anyone know what the hi-side pressure switch operates at? And does the V5 compressor have a pressure switch that drops out the clutch other than the switch at the condenser inlet? I didn't see one...

Thanks!

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"It ain't easy bein' cool..."

GM Tech on Wed July 14, 2010 7:32 AM User is offline

Keywords in your statement Cycling irregularly---- THIS IS A Malibu-- they also have control panel a/c master switch issues!

Watch your green light on the control head a/c b utton-- does it flicker when a/c compressor cuts-out? most likely since you said it is an intermttent on/off. If so you have the dreaded Malibu/Intrigue control head issue- which can be fixed by removing the control head- remove the blower motor selector switch which has the master a/c on/off brushes behind it. The brushes have poor contact because the grease put in there to save the brushes actually hinders them because it turns hard like earwax....so the easy solution- go buy a new control head for $125 or clean the brushes surface with a pencil head eraser- apply a new lite film of oil- bend brushes slightly to enable better force contact and re-install. I do about 2 a month this way with no comebacks...

Regular cycling (if it indeed does ever cycle) is a HPCO issue on a V-5 system which is a system designed not to cycle under normal operating conditions.


High pressure cut-out is 425 psi- off of the high side line transducer-a 3 wire pressure sensor- not a switch---

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Edited: Wed July 14, 2010 at 3:39 PM by GM Tech

k5guy on Wed July 14, 2010 3:26 PM User is offline

I'd also add that replacing the condenser when you replace the compressor is a good idea. Usually when a compressor goes bad, it throws trash into the condenser, and it will usually stay there.

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Squidward on Thu July 15, 2010 11:35 PM User is offlineView users profile

Quote
Originally posted by: GM Tech
Keywords in your statement Cycling irregularly---- THIS IS A Malibu-- they also have control panel a/c master switch issues!



Watch your green light on the control head a/c b utton-- does it flicker when a/c compressor cuts-out? most likely since you said it is an intermttent on/off. If so you have the dreaded Malibu/Intrigue control head issue- which can be fixed by removing the control head- remove the blower motor selector switch which has the master a/c on/off brushes behind it. The brushes have poor contact because the grease put in there to save the brushes actually hinders them because it turns hard like earwax....so the easy solution- go buy a new control head for $125 or clean the brushes surface with a pencil head eraser- apply a new lite film of oil- bend brushes slightly to enable better force contact and re-install. I do about 2 a month this way with no comebacks...



Regular cycling (if it indeed does ever cycle) is a HPCO issue on a V-5 system which is a system designed not to cycle under normal operating conditions.





High pressure cut-out is 425 psi- off of the high side line transducer-a 3 wire pressure sensor- not a switch---


Thanks! Incidentally, I saw the cleaning procedure of which you speak. After posting my last I spent hours looking for 99 Malibu schematics. Curiously, I kept coming across countless automotive forum posts about the flickering control LED and cycling compressor just like you described. Wow... I had no idea this was such a widespread issue. Here's the repair link.

I will have to pull the unit this weekend since I won't have time until Sunday. My daughter has been driving it this week, and she says it's been blowing cold without cycling issues since I taught her how to wiggle the fan speed selector switch and find the sweet spot that keeps the compressor on.

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"It ain't easy bein' cool..."

Squidward on Thu July 15, 2010 11:40 PM User is offlineView users profile

Quote
Originally posted by: k5guy
I'd also add that replacing the condenser when you replace the compressor is a good idea. Usually when a compressor goes bad, it throws trash into the condenser, and it will usually stay there.

Understood. I gave it a furious 90 psi backward/forward flush at least. The condenser flush came out much cleaner than the evap. But I think I got the system pretty well cleaned up before evac/recharge.

Thanks!



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"It ain't easy bein' cool..."

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