I finally charged up my AC system on my 71 Coupe with R12 and it blows nice and cold..
The only problem is that the Compressor is on all of the time regardless of the position of the switch on the console.
I am also getting a full 12 volts at the green wire that goes to the compressor even when the car is turned off.
I checked the micro switch on the console and it has continuity at all of the AC settings, but no continuity at the off or vent or defroster settings. So the switch checks good.
With a test light probed on the green compressor wire, the light goes out when I unplug the 3 wire anti dieseling Relay harness from the anti dieseling relay. Also the relay is warm to the touch with the key off.
Could one of the relays (blocker or anti dieseling) be stuck in the closed position causing current to flow to the Compressor with the switch and the ignition off? I unplugged the connector from the Compressor and took the cover off of the anti dieseling relay and plugged it back in.. this relay sems to be functioning properly.. the contacts are open when unplugged, and the contacts close when it is plugged back in..with the key off..something is switching this relay on with the key off.
If so, where would I locate the blocker or Anti dieseling relay? I looked on OReillys and Autozone websites as well as the major Corvette vendors and do not see the same relay listed...

Any ideas on how to fix this?

 

The temp/ac switch in my '80 L48 actuates the a/c using vacuum lines connected to solenoids in the dashboard area (inside the dash) as well as to a rectifier-style device that attaches to the a/c box in the engine bay. It sounds as if a key solenoid (or that rectifier component) that sends an electrical signal to your a/c has failed (always on). If you have a shop manual, take a close look at the schematic for a/c controls. Dr Rebuild's catalog is online and there may be a schematic for your 71 (or for the 68-82). Starting on page 52 of his latest catalog, there are diagrams and parts lists.

I'll take a look at my corvette rebuild books to see if there is something that talks about a/c controls/circuit and get right back to you this morning.

AHA, that corvette library of mine may finally pay off... I have a book by 'Prestige Publishing' titled 'Air Conditioning Strategies for the 63-82 Corvette (Written especially for the A/C illiterate)'... that is the actual book title. I'll take a look and advise...

 

Could it be the blower motor resistor? This is the 'rectifier style' component I referenced in my prior post. It typically is mounted under hood on the a/c housing. Wires typically run to the compressor and blower motor. I ended up replacing this resistor on my '80 vette to resolve NOT getting a/c compressor clutch engagement.

From Dr Rebuild's catalog, the item (with A/C):
G 69-71 with A.C. only Blower Motor Resistor
manufacturer "Indak". 9220412 $24.50

 

One [or both] switches on the A/C control unit have failed in the closed position...due to wear on the cam-button or because the contacts are corroded together. Power going to the compressor feeds through those switches so that the A/C is only ON for selected settings on the control wheel. So, it's probably time to 'dive' into the lower console to figure it all out.

The best source for vacuum and electrical schematics on that system are in the Chevrolet Chassis Service Manual in the 'Accessories' section for the A/C system. The general wiring diagram has no references to hookup of optional equipment.

 

I am pretty sure that my 71 is much different from the 1980 model..

According to the factory wiring diagram there is a tan wire that goes from the switch mounted on the Control wheel to the blocking relay..The vacuum has nothing to do with turning the comressor on or off.. it is switches and relays...

I confirmed that when I turn the AC on at both the terminal on the switch and at the relay connector it supplies current, but when turned off or to the defrost or vent positions it turns the current off at both locations.

What I am thinking is that the blocking relay is bad, and the compressor is running off of the anti dieseling relay...

 

Problem solved....


I wired in a standard Bosch type relay into the Blocker relay and left the anti dieseling relay unplugged and the AC Compressor is working perfect now...Goes on when it should and off when it should..

I think the Blocker relay was bad altogether, and the anti dieseling relay was stock in the on position.. I know there is a timer in the anti dieseling relay to supply power to the comressor for 5 seconds after the key is turned off so I assume that the timer is bad and allowing current to flow at all times...
I dont think I need the anti dieseling relay as I have had the AC disconnected for the past 4 months and have never had a dieseling problem..

I love it when a plan comes together.. I could not have done it without this forum....