A/C Relay in C3

[6shark9]

Can anybody save me some time locating the A/C relay module
in an 1969 C3?
I'm expecting it to be a small 3 connection plug-in module ('70s type GM usually right on the compressor.
I want to see if this is the reason that the compressor clutch fails to engage.

Any other help is appreciated,
6shark9

 

[RLS]

I am having the same problem that you are with my 72 only that the clutch does not engage from time to time. I will work for a while after you jump the leads, but then it will work for a while and then stop for no reason. My still gets a little voltage to the clutch but not enough to engage--almost like a bad relay. The AC guy thinks it is the anti desel relay that is some way tied into the AC system. I was told or saw something that this relay is located behind the passenger dash board on the plasitc cover. Do you know what to replace this relay with. I have a thread on the other corvette forum but have not had any luck. If you find out what the deal is I would appreciate it if you share you findings and I will do likewise.

 

[Mike Carter]

Are they properly charged? Low pressure will stop clutch engagement.

Welcome.

Mike

 

[RLS]

Mine is as it cools very well when it decides to honor me and come on. It is full of freon with no leaks.

 

[zwede]

Ok, here is the circuit on an early C3 (1971, other years similar):

Power comes in through the ignition switch on a 14 gauge brown wire. It goes to the heater control box in the console. In the control box there are 2 micro switches. Both have to be closed for the circuit to energize.

Next is a 16 gauge tan wire going from the second switch to the blocking relay mounted behind the passenger side dash pad, on the plastic heater core duct. The blocking relay is fed by the same switched power source as the control box. Wire is 18 gauge purple.

From the blocking relay there's a 16 gauge "LBL" (light-blue?) wire going through the firewall and goes to the low temperature shut off switch. The switch is located in the evaporator housing, on the engine compartment side of the system. From the switch is a 16 gauge dark green wire to the compressor.

Note: There is also an anti dieseling relay, but it can only switch the compressor on. Failure of this relay will not prevent the compressor from running (it's hooked up in parallell with the blocking relay).

Hope this helps.

/Markus

 

[RLS]

Thanks for the info, I have bought a ac/heater switch but mine checked good. Where is the other micro switch located on the controls? Do you know a source for that one? Also, what does the blocking relay do? Do you know a source for those as well. At this point I may replace all of them. I fired mine up earlier and the ac worked, but I did not turn off the controls the last time I drove it. Thanks for the help.

 

[zwede]

I think the second microswitch turns the AC off when you turn the thumbwheel to OFF. Both switches are located on the control unit so should be easy to find once you take the control out. Blocking relay saves the switches from having to pass the full current to the AC clutch.

/Markus

 

[RLS]

Makes sense, especially since mine does not seem to be getting full voltage at the clutch--Now where to get one at?

 

[zwede]

I've always had the best luck with Gary Gruhala (google for gruhala enterprises). He worked in the assembly plant back in the 60's and 70's and now sells parts. Prices are great and he's the most helpfull and nice person you'll ever find.

/Markus

 

[RLS]

Great, thanks for the help.