A/C - Unusual Problem
Thread Starter
6th Gear
Joined: Jun 2012
Posts: 6
Likes: 0
From: Weir Texas
A/C - Unusual Problem
I'm involved with an unusual problem with the HVAC on my 1979 'vette.
I have installed a new compressor (R-4) with new accumulator, etc. and the system is charged and working fine as far as cooling capability goes. There were some vacuum leaks, blown actuators, etc. but everything has been repaired and/or replaced.
The problem is that the a/c clutch will not engage when the two-wire connector is applied to the compressor. My meter shows twelve volts are present when measuring from the dis-connected connector, but when connected the voltage reading disappears and the clutch does not engage. It's like I have twenlve volts present, but only at one mil of current. If I apply a known twelve volt source to the compressor everything works perfectly.
Additionally, the fan will not run when the control slider is on the "vent" position. I don't know if these problems are related; I can't locate a wiring diagram that covers the HVAC and I'm at a loss as to why twelve volts at the compressor connection isn't strong wnough to operate the clutch winding.
Any help would certainly be appreciated and thank you very much in advance!!
Kind regards,
Landcranch
Melting Slicks
Joined: Oct 2006
Posts: 2,417
Likes: 336
From: Texas
i have a 79 also, i had to remove the control panel AC function switch and clean the contacts its the one in the console that the AC harness plugs into. you may also check that you are not loosing your 12 volts at one of the low press. or thermostatic switches inline to the compressor.
http://www.corvetteforum.net/c3/tune.../index16.shtml
http://www.corvetteforum.net/c3/tune.../index16.shtml
Last edited by speedreed8; Jun 22, 2012 at 03:03 PM.
Thread Starter
6th Gear
Joined: Jun 2012
Posts: 6
Likes: 0
From: Weir Texas
I certainly thank you for your reply! The connections on the low-pressure points are of interest now that you mention them, but without a schematic of the HVAC system these will be difficult to trace. I have several wiring diagrams but for some reason none show any wiring for cars with a/c!
I'll check as you have suggested and a sincere "Thanks" for your time!
Kind regardsm
Lamdcranch
I'll check as you have suggested and a sincere "Thanks" for your time!
Kind regardsm
Lamdcranch
Melting Slicks
Joined: Oct 2006
Posts: 2,417
Likes: 336
From: Texas
i have a schematic in the link in previous post. its for a 78 but is same as 79
http://www.corvetteforum.net/c3/tune.../index16.shtml
http://www.corvetteforum.net/c3/tune.../index16.shtml
Melting Slicks
Joined: Mar 2009
Posts: 3,126
Likes: 15
I'm involved with an unusual problem with the HVAC on my 1979 'vette.
I have installed a new compressor (R-4) with new accumulator, etc. and the system is charged and working fine as far as cooling capability goes. There were some vacuum leaks, blown actuators, etc. but everything has been repaired and/or replaced.
The problem is that the a/c clutch will not engage when the two-wire connector is applied to the compressor. My meter shows twelve volts are present when measuring from the dis-connected connector, but when connected the voltage reading disappears and the clutch does not engage. It's like I have twenlve volts present, but only at one mil of current. If I apply a known twelve volt source to the compressor everything works perfectly.
Additionally, the fan will not run when the control slider is on the "vent" position. I don't know if these problems are related; I can't locate a wiring diagram that covers the HVAC and I'm at a loss as to why twelve volts at the compressor connection isn't strong wnough to operate the clutch winding.
Any help would certainly be appreciated and thank you very much in advance!!
Kind regards,
Landcranch
Thread Starter
6th Gear
Joined: Jun 2012
Posts: 6
Likes: 0
From: Weir Texas
Mike - Thanks very much for your reply! I've been working on the problem most of the day and believe that I've located the cause. The pressure switch when closed shows a five hundred ohm resistance instead of a "no resistance" reading and I believe that is causing the current drop. If I "short around" this switch everything works normally so I'm convinced with the help of you gentlemen my troubles are over! Thanks for your kind reply and for your time!
Best,
Larry
Best,
Larry
Melting Slicks
Joined: Mar 2009
Posts: 3,126
Likes: 15
Mike - Thanks very much for your reply! I've been working on the problem most of the day and believe that I've located the cause. The pressure switch when closed shows a five hundred ohm resistance instead of a "no resistance" reading and I believe that is causing the current drop. If I "short around" this switch everything works normally so I'm convinced with the help of you gentlemen my troubles are over! Thanks for your kind reply and for your time!
Best,
Larry
Best,
Larry
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
6th Gear
Joined: Jun 2012
Posts: 6
Likes: 0
From: Weir Texas
Thanks for your reply! I most likely used the wrong term. The "Low Pressure Switch" has and is working normally; the problem was with the but-off switch with the sensor embedded in a tar-like substance on the side of the evaporator housing.
Everything (including this switch) was working fine during and after the charging process and then the entire system shut down. I immediately thought that the compressor clutch was not receiving current and when I found that it was but not in a "usable" amount that's when I began tracing the circuit to find where the resistance was.
I can't recall the name of the defective part, but I recognized the part from a photograph and have ordered a replacement. I'm certain that the charge is correct, but I sincerely appreciate your interest and your email!
This is a great forum and obviously frequented by a lot of great people!
Kind regards,
Landcranch
Everything (including this switch) was working fine during and after the charging process and then the entire system shut down. I immediately thought that the compressor clutch was not receiving current and when I found that it was but not in a "usable" amount that's when I began tracing the circuit to find where the resistance was.
I can't recall the name of the defective part, but I recognized the part from a photograph and have ordered a replacement. I'm certain that the charge is correct, but I sincerely appreciate your interest and your email!
This is a great forum and obviously frequented by a lot of great people!
Kind regards,
Landcranch
Melting Slicks
Joined: Mar 2009
Posts: 3,126
Likes: 15
Compressor cycling switch or freeze switch. Prevents evaporator from freezing by cycling off the compressor when supply air temp. or suction line gets to about 39 degrees or so. At least you will not lose the charge to change it. mike...
