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very high reading on high side

dan1554 on Tue October 20, 2009 10:11 PM User is offline

Year: 2003
Make: Chevy
Model: Impala
Engine Size: 3800
Refrigerant Type: r-134
Ambient Temp: 70
Pressure Low: 40
Pressure High: 400
Country of Origin: United States

I am having a problem with my 2003 Impala AC. Earlier this year (May) I had the condenser replaced, as it was bad. At that time, the system was vac'd down, it held vacuum, and they put a dye in to check for leaks. There were no leaks, and it blew ice cold air all summer. All other AC parts are original, and the car has 91,000 miles on it.

In the past few weeks, it would blow cold air, but then just stop, as though the compressor was shut off. Sometimes it would start again, and blow ice cold air. I checked it today, and on the low side I got about 40 psi, and the high side started at about 150 psi with the AC on, and rapidly went up to 400+ psi within about 10 seconds. The compressor would shut off, and pressure would drop back to about 150, the compressor would kick on again, and the pressure would jump to 400+ and shut the compressor off. A small amount of freon escaped when I took the gauge off the high side. After that, the compressor was running normally, the air was very cold, and the compressor did not shut off. I put the gauge back on, and it was staying around 175 consistently. The temperature was about 70.

Is this a blockage in the system somewhere? A friend suggested to me that the compressor is going bad, and the "suction side" is not sucking and that is why the pressure builds up. Any help is appreciated.

GM Tech on Tue October 20, 2009 10:25 PM User is offline

was coolant fan running when you experienced your high pressure cut-outs?

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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......

dan1554 on Tue October 20, 2009 10:29 PM User is offline

yes, the engine was at operating temperature, and both cooling fans were on.

mk378 on Tue October 20, 2009 11:18 PM User is offline

The compressor is working great. No problem there. Like GM Tech said, the usual reason for sudden rise in high side pressure (in a previously operating system) is failure of the condenser fans, which causes the condenser to overheat and stop condensing. If it's not that, there could be a blockage in the condenser or lines, but that's seems like it would be a constant problem when it happens.

dan1554 on Tue October 20, 2009 11:27 PM User is offline

I will have to check and make sure the fans stayed on. I know they both kicked on when I started the AC, but am not certain if they stayed on. Would the fan not running make the pressure rise that rapidly? (150 to 400+ in less than 10 seconds) What about when I am on the Interstate at 70 mph? That's when i first noticed the AC shutting off, but wouldn't the airflow simulate the fan? Thanks for your help.

bohica2xo on Tue October 20, 2009 11:32 PM User is offline

There is nothing wrong with a compressor that can produce 400 psi... yet. If it continues to cycle on the HPCO it will wear quickly however.

Why was the condensor replaced, and who replaced it? OEM part or aftermarket?

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

dan1554 on Tue October 20, 2009 11:42 PM User is offline

The condenser was replaced due to a major leak. It would not hold vacuum at all. My regular mechanic replaced it. I just looked at the invoice, and the part was listed at $232.48, I am not certain if it is OEM or aftermarket.

bohica2xo on Wed October 21, 2009 12:19 AM User is offline

Sounds like it is time to pull the OT and have a look.

Around here there is an ongoing issue with body shops doing A/C work after a collision. Chinese junk (or junkyard parts) to replace condensors, air deflectors & seals left off, etc. If you have a trusted mechanic this is probably not the case. Low bidder collision shops have screwed up a lot of A/C systems.

You have two fans, and three relays. The fans are two speeds. The circuit depends on both relays working, as well as a ground connection at the top left of the radiator support. It is possible that your fans are not working properly, or are erratic in operation.

You mentioned that it has cut out at highway speeds. It would be good to know if the system was hitting the HPCO at highway speeds, this would indicate something other than a fan issue.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

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