Hi
The prior owner removed the heater core and bypassed it.
The blower motor works perfect. The vent switch works.
The a/c had no belt on it and he said it hasn't worked in years.
I got the belt on, but there appears to be an extra plug on top, not sure what is for? See photo
Any advice? Thanks

 

Don't see the photo?

 

 

It's for the thermal limiter fuse. Follow the tan wire and it should be connected to a pin switch on the compressor rear head.

Its purpose is to shut the compressor off if the refrigerant charge goes low, either from normal leakage or a catastrophic loss of refrigerant. They'll also blow for no good reason.

You'll either have to install the thermal limiter fuse or install a jumper wire in its clip to get the compressor clutch to engage.

Suggest getting the 71 factory service manual if you don't have one. Airconditioning section covers the thermal limiter circuit. CSM actually recommends removing the fuse and installing jumper wire when charging the AC system.

 

One reason can be starting the engine with the AC on. You can start (or restart) the engine with the AC on a dozen times or more and not have a problem. Start or restart the engine that one time and the thermal limiter can pop. Why? I don’t know. This was pointed out to me many years ago and I’ve had it happen to me. Lesson learned. Shut the AC before shutting off the engine.

 

Once you get the AC clutch to engage you'll need a set of R12 gauges. You'll probably also need a vacuum pump. Chances are those hoses are no good if the AC hasn't worked for years.

 

Maybe not. The refrigerant oil coating on the inside may have preserved them some.

Have an AC shop pull a vacuum on the system and then see if it holds vacuum. That will tell the tale.

If it doesn't hold vacuum, pressurize the system with nitrogen (it's cheaper than R12) and sniff all hoses and connections for leaks. Repair as necessary and be prepared to fix more than you were counting on.

Up front, resurrecting a long-dormant AC system can get expensive. At the very least expect to repair most O-rings and replace the receiver-drier.

 

I took my 96 98 to a shop when the AC stopped cooling. $300 later with a new set of hoses and a fresh charge of R134a it cools great. The cheapest your going to get a vacuum pump and set of gauges is $300 from Horrible Freight. How long are those going to last?

 

Update, so tried starting it with the belt on and the compressor must be seized/frozen. Won't turn at all.
So looks like might be time to convert it to 134.
$$$ time

 

There are plenty of threads on our website on converting an R12 AC system to work with R134a. Here's a good place to start.

https://classicoldsmobile.com/forums...trofit-165565/

 

One advantage you have is the 68-72 A-body is popular enough that the aftermarket supports a R134A conversion with EVERYTHING. Remember that except for the control head whatever works on a Chevelle works on a Cutlass, Tempest and Skylark.

Look into a Sanden type compressor, a R134A-calibrated POA valve and possibly changing it to a cycling clutch system. You're into it for $$$ anyway, might as well make it easier to live with and more efficient.

Oh, you also get to ditch that aggravating thermal limiter fuse!

 

Love the quote "Horrible Freight" !!

 

Look on ebay for the gauges. I bought an old skool set of JB gauges. All brass with chrome metal ***** for i think 50 bucks. I think I got the vac pump from summit or Rockauto for like 160.