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Old 06-17-2017, 08:37 AM   #1
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AC Diagnosis Second Opinion??

I'm hoping somebody can confirm my diagnosis or suggest something I'm missing.

2006 GTO, intake and exhaust only. AC does not blow cold. I put a set of high and low gauges on it.

Ambient Conditions: 80*f 80%humidity

Gauge Readings:
Engine Off:
low 75psi high 75psi
Engine on 1500rpm
low 70psi high 100psi

Now I thought I should see:
Engine on 1500rpm
low 40psi high 240psi

Per the very limited diagnostic page in the Ellery book, all it says is this likely means the compressor is damaged?

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Old 06-17-2017, 11:03 AM   #2
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Looks about right. Chart i am looking at says weak compressor.
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Old 06-17-2017, 12:45 PM   #3
Fox Mulder
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It's a variable-displacement compressor, the vanes could be stuck. Not sure if there's a fix for that anyway, just worth a mention.
Before condemning the compressor, it might be worth having a shop evacuate the system and add the proper amount of refrigerant. Could just get it working, worst case it doesn't and you're probably out about $100 which you can consider a diagnostic fee. Maybe the shop will give you credit for that if they do the compressor replacement.
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Old 06-18-2017, 07:06 PM   #4
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I replaced a compressor on my old chevy truck on Friday. My final readings were 40/230 on a 90* day, so I could buy that the numbers you were expecting are pretty much normal.

However, the numbers you're getting do seem off. I can say that I almost replaced the compressor on my GTO (it is indeed a variable compressor, as mentioned) but then stumbled upon a thread that placed the blame somewhere - on a replaceable part in the actual compressor.

I was able to order one and actually replace this valve with the compressor still on the car (not much room to work, but doable)

Personally, I would research your symptoms against how a system reacts when the valve fails. It's been a couple of years, so I'm sorry but I can't remember how mine was acting; I do, however, still have the PDF from the research. (Edit, it won't let me attach as the PDF is too large - here's the link)

Last edited by Logan71; 06-18-2017 at 07:11 PM.
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Old 06-19-2017, 06:09 AM   #5
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I agree with Fox... Those readings can mean a restricted line, low refrigerant, or a bad cycling switch. Since you have gauges, I would first see if you have any freezing on the lines. That would indicate a restriction. I would then add some refrigerant since you have gauges... See if the pressures come up to normal. Or just go to a shop and have them discharge and fill to the exact amount and see where you are. The shop can always discharge the system for you if you end up needing a compressor.

There is a great diagnosis thread in the Body Shop forum by Konnie... It is a climate control system sticky and there is a full AC system section... Give that a read, good stuff.
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Old 06-19-2017, 04:37 PM   #6
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Hey, thanks for the help guys. I found the thread you mentioned when I was doing the testing. Looks like I need to do some more searching for other possible cause, but like I said the Ellery book, (Australian equivalent of a Haynes Manual) was pretty limited on AC diagnosis.

I forgot to add originally that the AC compressor seems quite loud when it runs. Almost as loud as the York single piston pump on my truck.

So while I search I will start setting aside some dollars to replace the compressor if that is actually what it turns out being.

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Old 06-19-2017, 04:54 PM   #7
Silvah Goat
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Originally Posted by WickedGoat...View Post
That would indicate a restriction.

A restriction would be indicated by either a high discharge or excessive suction. If a differential engine is not making a differential, it's either a moving a product that does not change phases, the metering device is not functioning properly (no restriction), or the engine itself is worn.

The refrigerant is indicating an ambient temp of 73, if the charge was low, it would have a very low suction also.

If the metering device is letting it all go through, there will not be a phase change, so the air would be cooled by the sensible heat gain only. Basically...nothing.
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