73 AC Compressor Won't Engage
Thread Starter
Racer
Joined: Apr 2004
Posts: 336
Likes: 0
From: Tucson
73 AC Compressor Won't Engage
Help...
The compressor won't kick in engage when the HVAC controls are moved to AC. The fan blows and I can hear the airflow doors move to different positions when I cycle through vent / heat / AC. Any ideas on how to isolate the problem?
Thanks
The compressor won't kick in engage when the HVAC controls are moved to AC. The fan blows and I can hear the airflow doors move to different positions when I cycle through vent / heat / AC. Any ideas on how to isolate the problem?
Thanks
Burning Brakes
Joined: Dec 2007
Posts: 889
Likes: 0
I have the same problem in my 74' - A/C was cold as ice last year - put the car in the garage in OCT and took the dash apart for interior work. Replaced exhaust manifolds, now the compressor will not engage. Fans work. I had forgotten to plug in the two-pin plug on top the compressor, still won't engage. Have not checked the fuze block yet. Hard to believe that a good system would lose enough freon over the winter to not come on??? But maybe so...
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Low freon; bad pressure switch; bad compressor clutch; defective switch(es) [mounted to sideplate of heater/A/C control head]; bad wiring/connector; 'fried' compressor.
Check to see if you are getting power to the compressor clutch connector (remove connector, wire up your voltmeter to the "hot" pin and chassis ground, turn ON and see if you get 12 volts to show up; also verify good ground connection to the other side of that connector with your ohmmeter). If you are getting power to the compressor, the problem has to be one of the other components.
Check to see if you are getting power to the compressor clutch connector (remove connector, wire up your voltmeter to the "hot" pin and chassis ground, turn ON and see if you get 12 volts to show up; also verify good ground connection to the other side of that connector with your ohmmeter). If you are getting power to the compressor, the problem has to be one of the other components.
Thread Starter
Racer
Joined: Apr 2004
Posts: 336
Likes: 0
From: Tucson
Low freon; bad pressure switch; bad compressor clutch; defective switch(es) [mounted to sideplate of heater/A/C control head]; bad wiring/connector; 'fried' compressor.
Check to see if you are getting power to the compressor clutch connector (remove connector, wire up your voltmeter to the "hot" pin and chassis ground, turn ON and see if you get 12 volts to show up; also verify good ground connection to the other side of that connector with your ohmmeter). If you are getting power to the compressor, the problem has to be one of the other components.
Check to see if you are getting power to the compressor clutch connector (remove connector, wire up your voltmeter to the "hot" pin and chassis ground, turn ON and see if you get 12 volts to show up; also verify good ground connection to the other side of that connector with your ohmmeter). If you are getting power to the compressor, the problem has to be one of the other components.
Pro
Joined: May 2011
Posts: 581
Likes: 5
From: BC
I have the same problem in my 74' - A/C was cold as ice last year - put the car in the garage in OCT and took the dash apart for interior work. Replaced exhaust manifolds, now the compressor will not engage. Fans work. I had forgotten to plug in the two-pin plug on top the compressor, still won't engage. Have not checked the fuze block yet. Hard to believe that a good system would lose enough freon over the winter to not come on??? But maybe so...
In your case however, you were in the neighbouthood of several items critical to the A/C circuitry. Double check all your connections. A wiring diagram will point out the low pressure switch which is the easiest way with a test light to tell if you are simply low on refrigerant.
Steve
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 99
From: Ontario
In your case however, you were in the neighbourhood of several items critical to the A/C circuitry. Double check all your connections. A wiring diagram will point out the low pressure switch which is the easiest way with a test light to tell if you are simply low on refrigerant.
And what is that test? My problem is the opposite of the OP: my compressor clutch engages when A/C is selected on the console controls but does not dis-engage (i.e. cycle).
And what is that test? My problem is the opposite of the OP: my compressor clutch engages when A/C is selected on the console controls but does not dis-engage (i.e. cycle).
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
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 99
From: Ontario
No, no cooling but now that I have found the sightglass (with help here) I can see fluid. Of course what that means I do not know. The joy of being ignorant about these things.
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 99
From: Ontario
No I have not changed anything. I am trying to get stock things in good order. Yesterday I noticed the terminals on the low pressure switch were corroded and I will change those today. But realistically the system needs a professional diagnosis and probably a re-charge. My objective is to get the wiring flaws out of the way (e.g. the HI-fan and 30-amp fuse matters) before the diagnosis proceeds. I do not wish to frustrate the technician - and me - with such issues at $100/hr.
Melting Slicks
Joined: Mar 2009
Posts: 3,126
Likes: 15
The fluid is probably oil. Tells me there is flow from the comp. but most likely low on refig. When the comp. is turned off do you have any pressure on the Schrader valve/service port? mike.
Yes, ...roger...
Yes, ...roger...
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 99
From: Ontario
I am reluctant to touch those valves as I do not have the equipment to see pressure.
Melting Slicks
Joined: Mar 2009
Posts: 3,126
Likes: 15
I understand. They are no different than a tire stem valve. Remove the cap and press the stem with a small screwdriver while wearing eye protection and see if there is any pressure at all. Some oil/refig. may come out. This will help to determine if you have any refig. at all. I am betting there is very little pressure. Just do not do it while the comp. is running as you could suck in air. mike...
Thread Starter
Racer
Joined: Apr 2004
Posts: 336
Likes: 0
From: Tucson
And now back to the original post topic...
While checking things out tonight, I discovered a loose wire (see "A" in the pic). Does anyone know where it should be connected to? The loose end is long enough to reach the back of the compressor plus a few inches, but I don't see connectors missing a wire. I'm hoping this is the culprit causing the compressor not to engage.
http://rides.webshots.com/album/580270695ReDMes
http://rides.webshots.com/photo/2269...67542063RGfORK
While checking things out tonight, I discovered a loose wire (see "A" in the pic). Does anyone know where it should be connected to? The loose end is long enough to reach the back of the compressor plus a few inches, but I don't see connectors missing a wire. I'm hoping this is the culprit causing the compressor not to engage.
http://rides.webshots.com/album/580270695ReDMes
http://rides.webshots.com/photo/2269...67542063RGfORK
Last edited by Ran-D; May 30, 2011 at 03:27 AM.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Randy , where does A go and what does the loose end look like ?
...................
Lets talk about B in your pic. B is the thermal fuse and its probably blown.Try this to start.
Unplug B from the connector
start the engine and turn the AC on
in the connect there should be 2 dk green wires
use a paper clip and jumper the 2 dk green wires momentarily to see if comp kicks on,pull clip out if comp comes on
(hopefully the wires are plugged in at the comp)
...................
Lets talk about B in your pic. B is the thermal fuse and its probably blown.Try this to start.
Unplug B from the connector
start the engine and turn the AC on
in the connect there should be 2 dk green wires
use a paper clip and jumper the 2 dk green wires momentarily to see if comp kicks on,pull clip out if comp comes on
(hopefully the wires are plugged in at the comp)
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
And now back to the original post topic...
While checking things out tonight, I discovered a loose wire (see "A" in the pic). Does anyone know where it should be connected to? The loose end is long enough to reach the back of the compressor plus a few inches, but I don't see connectors missing a wire. I'm hoping this is the culprit causing the compressor not to engage.
http://rides.webshots.com/album/580270695ReDMes
http://rides.webshots.com/photo/2269...67542063RGfORK
While checking things out tonight, I discovered a loose wire (see "A" in the pic). Does anyone know where it should be connected to? The loose end is long enough to reach the back of the compressor plus a few inches, but I don't see connectors missing a wire. I'm hoping this is the culprit causing the compressor not to engage.
http://rides.webshots.com/album/580270695ReDMes
http://rides.webshots.com/photo/2269...67542063RGfORK
If the compressor gets over 140° then it will trip that wire to ground and blow the thermal limiter (like a fusable link) at the 3 prong connecter .
http://www.oreillyauto.com/site/c/se...972&vi=1410084
In short, that circuit must be good to have power to the a6 clutch.
Hope that makes sense to you.
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
A simple proceedure for r12 was to fill the system with 12 with the compressor running until the refrigerant bubbles stopped in the sight glass.
That won't work for 134, solid flow will be an overcharge.
If your valves are like tire valves you are still setup for r12.
If the valves are bigger and don't have external threads then it's been converted to 134.
You can now find r12 as cheap as the retail 134 in 12oz cans, so it may be cost effective to get with a forum member across the border to recharge with that. Nothing wrong with the original stock system performance.