Pressure Release Noise - A/C Problem?
Thread Starter
Pro
Joined: Sep 2006
Posts: 655
Likes: 114
From: Orange County, Southern California
Pressure Release Noise - A/C Problem?
Was driving along, cool morning (65 degrees outside), auto climate control on, about 30 mph - suddenly heard an extremely loud "hissing" sound, 
(like a water hose bursting or freon line bursting), loud pressure release sound for about 8 seconds, then all went quiet (and hasn't repeated since). Took it to the dealer (under warranty, has about 8,000 miles), and they can't find anything wrong. Appears to be no coolant leaks, or freon leaks since. They said it was slightly low on freon, so recharged the system. Their "guess" is that freon released out of the pressure release valve on the compressor because "maybe it was overfilled at the factory". (The car is 2 years old now, but waited until now? 
I also checked the shop manual, and sure enough, there indeed is a "pressure release valve" on the compressor.)
Problem is, it's cool / chilled, but definately not as cold as it used to be (nor as cold as my other car) = the A/C is not working as efficiently as it used to. Has anyone else experienced this, or have any idea what I should check? I've checked both low and high side A/C pressure and appears to be within specs. Any ideas? Thx.
(like a water hose bursting or freon line bursting), loud pressure release sound for about 8 seconds, then all went quiet (and hasn't repeated since). Took it to the dealer (under warranty, has about 8,000 miles), and they can't find anything wrong. Appears to be no coolant leaks, or freon leaks since. They said it was slightly low on freon, so recharged the system. Their "guess" is that freon released out of the pressure release valve on the compressor because "maybe it was overfilled at the factory". (The car is 2 years old now, but waited until now? I also checked the shop manual, and sure enough, there indeed is a "pressure release valve" on the compressor.)Problem is, it's cool / chilled, but definately not as cold as it used to be (nor as cold as my other car) = the A/C is not working as efficiently as it used to. Has anyone else experienced this, or have any idea what I should check? I've checked both low and high side A/C pressure and appears to be within specs. Any ideas? Thx.
Safety Car
Joined: Sep 2008
Posts: 4,296
Likes: 156
From: Location: Location: kAnSaS
Was driving along, cool morning (65 degrees outside), auto climate control on, about 30 mph - suddenly heard an extremely loud "hissing" sound, (like a water hose bursting or freon line bursting), loud pressure release sound for about 8 seconds, then all went quiet (and hasn't repeated since). Took it to the dealer (under warranty, has about 8,000 miles), and they can't find anything wrong. Appears to be no coolant leaks, or freon leaks since. They said it was slightly low on freon, so recharged the system. Their "guess" is that freon released out of the pressure release valve on the compressor because "maybe it was overfilled at the factory". (The car is 2 years old now, but waited until now? I also checked the shop manual, and sure enough, there indeed is a "pressure release valve" on the compressor.)
Problem is, it's cool / chilled, but definately not as cold as it used to be (nor as cold as my other car) = the A/C is not working as efficiently as it used to. Has anyone else experienced this, or have any idea what I should check? I've checked both low and high side A/C pressure and appears to be within specs. Any ideas? Thx.
(like a water hose bursting or freon line bursting), loud pressure release sound for about 8 seconds, then all went quiet (and hasn't repeated since). Took it to the dealer (under warranty, has about 8,000 miles), and they can't find anything wrong. Appears to be no coolant leaks, or freon leaks since. They said it was slightly low on freon, so recharged the system. Their "guess" is that freon released out of the pressure release valve on the compressor because "maybe it was overfilled at the factory". (The car is 2 years old now, but waited until now? I also checked the shop manual, and sure enough, there indeed is a "pressure release valve" on the compressor.)Problem is, it's cool / chilled, but definately not as cold as it used to be (nor as cold as my other car) = the A/C is not working as efficiently as it used to. Has anyone else experienced this, or have any idea what I should check? I've checked both low and high side A/C pressure and appears to be within specs. Any ideas? Thx.
there is a pressure release valve yes,,,,its just a safety measure so it doesnt blow a line and that high head pressure has a place to go. A couple things could cause your system to go high enough to release like that.
The most common cause would be the radiator fans NOT coming on (either the relay faulty, fan faulty or sensor wiring issue etc..) causing the high side pressure to go crazy. If the pressure was that high and returned to normal i doubt you have a restriction.
My guess is its not an AC problem as much as it is an electrical issue in the fan system. IMO, good luck paul
Racer
Joined: Oct 2005
Posts: 371
Likes: 0
From: Long Valley NJ
If your high pressure relief valve vented the system there would have been oil all over the area of the spray. Did you notice this had happened when you opened the hood? No way it vented without doing leaving an oil mess. Do a temperature check with a thermometer in the center dash outlets with the system on outside air, fan at max and a minimum set point for the temperature. You should see a minimum of a 25 degree drop at the outlets from ambient. Try to keep the RPM's at or above 1500. Regardless, the system should be able to acheive a discharge temp of 45F sitting in your driveway.
Hopefully it is still hot where you live.
Hopefully it is still hot where you live.
Last edited by Greenvetter; Sep 20, 2008 at 11:53 AM.
Melting Slicks
Joined: Sep 2007
Posts: 2,597
Likes: 3
From: READING PA
St. Jude Donor '08-'09-'10
If your high pressure relief valve vented the system there would have been oil all over the area of the spray. Did you notice this had happened when you opened the hood? No way it vented without doing leaving an oil mess. Do a temperature check with a thermometer in the center dash outlets with the system on outside air, fan at max and a minimum set point for the temperature. You should see a minimum of a 25 degree drop at the outlets from ambient. Try to keep the RPM's at or above 1500. Regardless, the system should be able to acheive a discharge temp of 45F sitting in your driveway.
Hopefully it is still hot where you live.
Hopefully it is still hot where you live.
That should happen first before the relief valve would open. I hope when you took it to the garage it did not have a "empty charge". In that event they just cant fill it with freon 134a. The system should be checked for leaks then a vacuum must be pulled before admitting any freon. This is basic stuff but there is always someone out there who will try to fill it with moisture in the system. Then it will never work properly. Good luck at the garage. Make sure they leak check it.
Race Director
Joined: Apr 2008
Posts: 17,373
Likes: 6
From: Chatsworth California
there is a pressure release valve yes,,,,its just a safety measure so it doesnt blow a line and that high head pressure has a place to go. A couple things could cause your system to go high enough to release like that.
The most common cause would be the radiator fans NOT coming on (either the relay faulty, fan faulty or sensor wiring issue etc..) causing the high side pressure to go crazy. If the pressure was that high and returned to normal i doubt you have a restriction.
My guess is its not an AC problem as much as it is an electrical issue in the fan system. IMO, good luck paul
The most common cause would be the radiator fans NOT coming on (either the relay faulty, fan faulty or sensor wiring issue etc..) causing the high side pressure to go crazy. If the pressure was that high and returned to normal i doubt you have a restriction.
My guess is its not an AC problem as much as it is an electrical issue in the fan system. IMO, good luck paul
Thread Starter
Pro
Joined: Sep 2006
Posts: 655
Likes: 114
From: Orange County, Southern California
Yes, pulled vacuum, and evidence of the release
Thank you all for the great leads. Yes, right after the "depressurization event", I immediately took the car to the local Southern California Chevy Dealer, who pulled a full vacuum (which they say held), and then recharged (along with the correct amount of oil). Also, yes, there was evidence of freon / oil spray in the engine compartment. Thx, again, for the responses.
Thread Starter
Pro
Joined: Sep 2006
Posts: 655
Likes: 114
From: Orange County, Southern California
Just to Finish the Story (It was the A/C Compressor)
Just to close the loop - got the car (2006 coupe, Electronic Climate Control, Auto) - and the dealer replaced the A/C compressor under warranty (quite a lot of labor due to having to drop the right front suspension to switch out the A/C compressor). Preliminarily, at least (only got to drive it home), it appears to be a "freezer unit" once again = it's working great, just like it did prior to the "pressure release" incident. So, indications are that something happened in the compressor which had cause the compressor pressure release valve to release, and never work correctly again. Hopefully, all better now! Thx to those who gave me input!
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