'92 vette air conditioning issue
Thread Starter
Heel & Toe
Joined: Jun 2008
Posts: 18
Likes: 0
From: Maryville Tennessee
'92 vette air conditioning issue
I have a 1992 coupe, and spent some time this weekend trying to get the a/c running for the summer. The coppressor won't engage for some reason. If I ground one of the two wires that plug into the low pressure side switch, the compressor comes on and runs like a champ. If I cross the two wires, nothing happens. I belive I have a good charge of refrigerant, as I grounded the wire for about 10 minutes and let the system run on high and air temp. out of the middle vent in the car was 50 degrees. My first thought is that the switch is bad, but don't know for sure. I more used to working on 40 year old muscle cars and don't know all the in's and out's of the Vette yet.
Instructor
Joined: May 2008
Posts: 234
Likes: 1
From: Midland Texas
Low side switch
Try disconnecting the battery for 5 to 10 min to reset the AC computer, if the low side switch cycles to much you AC computer will shut down the AC to keep from damaging the compressor the low side switch is just a switch it shorts or opens the two wires with pressure, so if you have to ground a wire to get it to work something is causing that to be open becuse when I charge these sysytem I jumper the two wires together with a paperclip to get the AC to run long enough to charge it
Instructor
Joined: Sep 2004
Posts: 177
Likes: 2
From: Palmyra Virginia
I have same issue with my 92, first thing to look at is wether or not the light is blinking on the a/c controller when car is first started. (This assumes you have the electronic controlled a/c). We thought the switch was bad on mine but after some more troubleshooting have determined that the controller and /or programmer is bad. Have new contoller, programmer is currently on back order. Decided to just go ahead and replace both.
Cruising
Joined: May 2005
Posts: 14
Likes: 0
From: Gettysburg PA
I was just doing some diagnosing on my system...all I can tell you is buy the factory service manual. Step by step to troubleshoot. Did the same with the brake light. Almost replaced the mastercylinder and it turned out to be a short in the wire.
8th Gear
Joined: May 2008
Posts: 8
Likes: 0
I have a 1992 coupe, and spent some time this weekend trying to get the a/c running for the summer. The coppressor won't engage for some reason. If I ground one of the two wires that plug into the low pressure side switch, the compressor comes on and runs like a champ. If I cross the two wires, nothing happens. I belive I have a good charge of refrigerant, as I grounded the wire for about 10 minutes and let the system run on high and air temp. out of the middle vent in the car was 50 degrees. My first thought is that the switch is bad, but don't know for sure. I more used to working on 40 year old muscle cars and don't know all the in's and out's of the Vette yet.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Thread Starter
Heel & Toe
Joined: Jun 2008
Posts: 18
Likes: 0
From: Maryville Tennessee
a/c issue
The low pressure switch is on the low pressure line and is close to where the line enters the box at the firewall. I believe this should be the bigger of the two refrigerant lines and the one that goes into the drier before it goes into the compressor. It has two wires plugged into it. Unplug the wires from the switch and run a jumper between them and see what happens. Nothing happened on mine, but when I ground one of the wires instead of jumping them together it comes right on. Try grounding each wire seperately to figure out which one works and let me know. I have not solved my problem yet, by the way.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
The Low Pressure Switch, in line with the Compressor Relay, cuts power to the Compressor when the pressure is low enough to ice up the Evaporator. For this Year, that relay is driven by the ECM and since grounding one of the leads runs the Compressor, your ECM isn't getting the a/c request or it's broken. Do clear memory from the Controls by disconnecting and reconnecting the battery and then hookup a scanner to verify the a/c request. You can also run diagnostics - go here: https://www.corvetteforum.com/techti...=193&TopicID=2
Finally, mixing R12 and Freeze 12 (which is 80% R134) can raise operating pressures to the point that it blows up. The Pressure Sensor, on the high pressure line, relays that situation to the ECM and ground is removed from the Relay before there's a hole in your hood. I wouldn't jumper anything (for more time than it takes to see what the pressure is - either with a Scanner or Manifold Gage Set - and stand clear while you're trying to figure it out).
Finally, mixing R12 and Freeze 12 (which is 80% R134) can raise operating pressures to the point that it blows up. The Pressure Sensor, on the high pressure line, relays that situation to the ECM and ground is removed from the Relay before there's a hole in your hood. I wouldn't jumper anything (for more time than it takes to see what the pressure is - either with a Scanner or Manifold Gage Set - and stand clear while you're trying to figure it out).
Last edited by SunCr; Jun 3, 2008 at 12:12 PM.
Thread Starter
Heel & Toe
Joined: Jun 2008
Posts: 18
Likes: 0
From: Maryville Tennessee
I disconnected the battery for 15 minutes and then re-connected. Compressor came on and ran fine. What's the deal with the pressure mixing r12 and freeze12? Sounds like I may need to evacuate the system and recharge?
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
The legal part is here:
http://www.epa.gov/Ozone/snap/refrig.../macssubs.html
The chemistry is that two unlike refrigerants will fractionate and raise system pressure - maybe to the point of blowing a hole in something, but more importantly, as the gas leaks out - and you've got a leak if you're topping off with anything - there won't be enough gas to carry the oil charge. And since the pressure is too high to open the Low Pressure Switch Contacts, your compressor seizes, chucks a bunch of metal into everything, and you're looking at a complete rebuild. I don't know what the manufacturer of Freeze 12 is claiming or marketing (I don't touch the stuff since plain old R12 is still readily available), but I've got a feeling that somewhere in the small print they tell you to start with an empty system. If you want to use R12, get your license to buy it at www.epatest.com and if you can't pass the online test, quit fooling around with a/c. And then try Autozone for R12 because they've long since realized that no-one really wants it anymore and even at 15 Bucks a can (the most I've paid there - often it's lower), the 3 cans you need for a complete charge is 9 or 10 gas fillups less than what a complete rebuild will cost you (assuming you can do it yourself - double that for a shop).
http://www.epa.gov/Ozone/snap/refrig.../macssubs.html
The chemistry is that two unlike refrigerants will fractionate and raise system pressure - maybe to the point of blowing a hole in something, but more importantly, as the gas leaks out - and you've got a leak if you're topping off with anything - there won't be enough gas to carry the oil charge. And since the pressure is too high to open the Low Pressure Switch Contacts, your compressor seizes, chucks a bunch of metal into everything, and you're looking at a complete rebuild. I don't know what the manufacturer of Freeze 12 is claiming or marketing (I don't touch the stuff since plain old R12 is still readily available), but I've got a feeling that somewhere in the small print they tell you to start with an empty system. If you want to use R12, get your license to buy it at www.epatest.com and if you can't pass the online test, quit fooling around with a/c. And then try Autozone for R12 because they've long since realized that no-one really wants it anymore and even at 15 Bucks a can (the most I've paid there - often it's lower), the 3 cans you need for a complete charge is 9 or 10 gas fillups less than what a complete rebuild will cost you (assuming you can do it yourself - double that for a shop).
Safety Car
Joined: Oct 2007
Posts: 3,816
Likes: 0
From: :45 minutes from everywhere / E-I-E-I-O
The legal part is here:
http://www.epa.gov/Ozone/snap/refrig.../macssubs.html
The chemistry is that two unlike refrigerants will fractionate and raise system pressure - maybe to the point of blowing a hole in something, but more importantly, as the gas leaks out - and you've got a leak if you're topping off with anything - there won't be enough gas to carry the oil charge. And since the pressure is too high to open the Low Pressure Switch Contacts, your compressor seizes, chucks a bunch of metal into everything, and you're looking at a complete rebuild. I don't know what the manufacturer of Freeze 12 is claiming or marketing (I don't touch the stuff since plain old R12 is still readily available), but I've got a feeling that somewhere in the small print they tell you to start with an empty system. If you want to use R12, get your license to buy it at www.epatest.com and if you can't pass the online test, quit fooling around with a/c. And then try Autozone for R12 because they've long since realized that no-one really wants it anymore and even at 15 Bucks a can (the most I've paid there - often it's lower), the 3 cans you need for a complete charge is 9 or 10 gas fillups less than what a complete rebuild will cost you (assuming you can do it yourself - double that for a shop).
http://www.epa.gov/Ozone/snap/refrig.../macssubs.html
The chemistry is that two unlike refrigerants will fractionate and raise system pressure - maybe to the point of blowing a hole in something, but more importantly, as the gas leaks out - and you've got a leak if you're topping off with anything - there won't be enough gas to carry the oil charge. And since the pressure is too high to open the Low Pressure Switch Contacts, your compressor seizes, chucks a bunch of metal into everything, and you're looking at a complete rebuild. I don't know what the manufacturer of Freeze 12 is claiming or marketing (I don't touch the stuff since plain old R12 is still readily available), but I've got a feeling that somewhere in the small print they tell you to start with an empty system. If you want to use R12, get your license to buy it at www.epatest.com and if you can't pass the online test, quit fooling around with a/c. And then try Autozone for R12 because they've long since realized that no-one really wants it anymore and even at 15 Bucks a can (the most I've paid there - often it's lower), the 3 cans you need for a complete charge is 9 or 10 gas fillups less than what a complete rebuild will cost you (assuming you can do it yourself - double that for a shop).
Last time I noticed a can on the shelf at the Advance/Zone, it was $35 for a 12oz can - NC, 2003, I think...
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Must be the fuel surcharge - any of 3 Autozones within 15 miles of where I live. Once, on the same day, I found it for $12 to the South; $14 to the East, and $15 to the North. I figured the closer I got to Mexico (where it's about $4/can), the cheaper it got. Amazingly enough, not all of it was the same manufacturer (I bought all of 6 cans - 3, 2 & 1 wiping out what each store had). $35/can is $47/lb - that's absurd! When I've asked, NAPA has usually quoted $25 to $30/lb, but they only sell it in 12 lb jugs which I had/have no use for. For once, the rebuild I did on the Vette seems to have held up and I didn't break anything else, so I don't have any use for any of it right now and I haven't been shopping in awhile. The last refrigerant I bought was R134 - at the time, Dupont announced they couldn't make enough ro meet OEM production and prices had shot up to $8/can. All I can say is shop around. Not many Yugos out there worth the price of a new compressor so no one really wants it other than guys like us.
Instructor
Joined: Oct 2006
Posts: 245
Likes: 0
From: Catawissa Pa
I had the same problem, except I have R134 in the system. I reset the computer by disconnecting the battery. While the compressor was engaged I added R134 to fill the system. It has worked fine for the last month. I think I have it fixed. When the compressor cycles on and off too often within a certain time period, because of low pressure, the computer won`t let the compressor kick in.
