I've got a '79 450 SL and since I've owned it, the Air Conditioning has never worked. Not important to me, but thanks to another thread on this forum I have successfully removed my leaky radiator, and it's now at a local shop. Meanwhile, I am looking into the engine compartment and the A/C compressor is staring me in the face, and from looking around, I see that the first thing in removing/replacing the compressor, is to remove the radiator.

The question is, how to determine if the compressor is likely a problem...it may be fine, but something as simple as a fuse could have the whole thing out of commission. (Actually I did already check the fuse and it's good!)

Here are some observations:

Forward on the compressor, is a two pin connector. I've checked the resistance accross these pins on the compressor side, and they read zero or near zero ohms. Conclusion: The coils or some protection inside is not damaged.

Turning on the A/C (Ignition on, engine not running) does not result in 12 V at the line side of that 2 pin compressor connector.

I read somewhere regarding a newer model, that the aux fan comes on when the A/C is turned on. Today, switching on the A/C (ignition on but not running engine), did not put 12 V at the aux. fan, as is the case when the temp switch is grounded at the thermostat housing.

The clutch assembly turns smoothly, albeit with slight resistance. I presume this to tell me the bearings are not seized.

When the engine was running (before the radiator was removed), switching on the A/C in the cockpit gave no response as far as we could see at the compressor, and the auxiliary fan did not come on either (but that is broken).

I understand there may be an A/C relay that may be the culprit. I have no idea where to look for that.

I expect any R12 is long gone.

I'm thinking the best strategy would be to confirm as best I can that the compressor is not bad, before I put back the radiator, identify any electrical problems, and then get the car to an A/C shop for vacuum test and new refrigerant with dye.

Any advice as far as the compressor or the electrical checkout is much appreciated. It's been a result of prior threads that I was even able to make (what I hope are somewhat intelligent) observations.s

Thanks much.

Stu