85 A/C High Pressure Line?
Thread Starter
Melting Slicks
Joined: Feb 2005
Posts: 2,057
Likes: 5
From: Bay Shore, NY
85 A/C High Pressure Line?
I've been troubleshooting my a/c system in my 85 since I've had some spare time and I have some questions. First, I was testing to see if the main cooling fan was working properly because it does not come on with the A/C in the MAX position. It does come on at 238 degrees though. I followed the diagnostic flowchart and pulled the fan switch on the high pressure line and the fan came on. According to the flowchart it says replace the switch. Is that correct? The a/c system in the car seems empty, I get no pressure reading at the drier or the high pressure line.
The line the fan control switch plugs into is all corroded too at the base of where the 2 switches are plugged in, I think I may have found the leak there, but I'm not sure until I test it. Anyway, I'd like to replace the line just for the hell of it, but I don't see a listing for it in any catalogue or even in my parts manual. Its illustrated, but no numbers are given. Matter of fact, I don't see a listing for the fan control switch either. Anyone have part numbers for these parts or point me to a place that does? I've looked at Ecklers, Corvette America and Corvette Central and even P&G Chevy, but nothing comes up. Something tells me they are disco'd.
Any help is appreciated.
The line the fan control switch plugs into is all corroded too at the base of where the 2 switches are plugged in, I think I may have found the leak there, but I'm not sure until I test it. Anyway, I'd like to replace the line just for the hell of it, but I don't see a listing for it in any catalogue or even in my parts manual. Its illustrated, but no numbers are given. Matter of fact, I don't see a listing for the fan control switch either. Anyone have part numbers for these parts or point me to a place that does? I've looked at Ecklers, Corvette America and Corvette Central and even P&G Chevy, but nothing comes up. Something tells me they are disco'd.
Any help is appreciated.
Last edited by ejscarfo; Aug 21, 2008 at 02:09 PM.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
The fan switch contacts open at 220 to 240 psi and when the signal voltage rises at the ECM, it grounds the Main Relay. Contacts reclose at 170 to 190 psi, the signal voltage drops back to zero, and the ECM removes ground from the Relay (as long as the Coolant Temp Signal is below 226 degrees). If there's no gas - or not enough gas - the pressure will not build to the switch's threshold for fan operation. You need to hook up a manifold gage set to see. You need to scan it to see the Coolant Temp Signal. Your ECM is obviously ok because disconnecting the harness cranks the fan on.
I wouldn't replace a perfectly good line - switch is available at NAPA or GM. It's mounted on a Schrader, and if that's leaking, it can be replaced.
I wouldn't replace a perfectly good line - switch is available at NAPA or GM. It's mounted on a Schrader, and if that's leaking, it can be replaced.
Thread Starter
Melting Slicks
Joined: Feb 2005
Posts: 2,057
Likes: 5
From: Bay Shore, NY
The fan switch contacts open at 220 to 240 psi and when the signal voltage rises at the ECM, it grounds the Main Relay. Contacts reclose at 170 to 190 psi, the signal voltage drops back to zero, and the ECM removes ground from the Relay (as long as the Coolant Temp Signal is below 226 degrees). If there's no gas - or not enough gas - the pressure will not build to the switch's threshold for fan operation. You need to hook up a manifold gage set to see. You need to scan it to see the Coolant Temp Signal. Your ECM is obviously ok because disconnecting the harness cranks the fan on.
I wouldn't replace a perfectly good line - switch is available at NAPA or GM. It's mounted on a Schrader, and if that's leaking, it can be replaced.
I wouldn't replace a perfectly good line - switch is available at NAPA or GM. It's mounted on a Schrader, and if that's leaking, it can be replaced.
