Air conditioning or quantum physics... which is less complicated??

[jassz]

I have been reading a lot of threads on the subject (did a search), but there seem to be many parts and many possible sources for problems. Where to start??

Okay... we have a 1981 300td. It came without a belt on the airconditioning compressor. I knew it wouldn't be as simple as just putting a belt on, but I was hoping. Sigh, it didn't work. THe compressor does not engage. There did seem to be gas pressure in the line (could hear a hiss after turning that little valve). I know that if there is no pressure the clutch won't move and the compressor won't come on. In order to eliminate that as a possibility, my husband hooked it up to a voltage meter, and there is no power going to the compressor at all. I can't see that there is a fuse for the airconditioner. Maybe a relay switch? Or the compresser itself?

I talked to our mechanic breifly about it and she said if it had been sitting any length of time without running, the compressor would have to be replaced. She said not to bother with rebuilt as she went through 3 before finally buying a new one. I checked out the price of a new one, and it's about $600+. At that price we'll be using the 2/60 AC... 2 windows down and travelling 60mph!). She also said we'd need an R134 upgrade kit. (In Canada they try to discourage the use of the other kind of refrigerant because it is bad for the environment. They dont' outlaw it, they just price it out of reach).

I'm not sure if it's related, but I'll mention it in case it is... the heater also doesn't work properly. Or actually the HEAT works, but the temperature setting makes no difference. The only choices are HOT and Burn the Hair in Your Nostrils. From what I've read here it sounds like that could be the monovalve??? Is that a separate problem from the AC issue?

What would be the most logical thing to try first? (and second and third). Someone on ebay is selling 'everything needed for hte AC system from the firewall forward'. It's kind of tempting! But, my luck the problem is on the other side of the firewall.

Thanks!