I just picked up a 1979 300D with a non-functioning A/C. I’ve read about converting from the OEM compressor to an aftermarket compressor. I was thinking about doing something similar, although I would like to go with a more economical Ford or GM standard compressor and drier (and other parts, if necessary).

Although I am not an A/C expert, it looks to me like the 300 D A/C system controls are vacuum operated. [There is a unit next to the compressor that has several vacuum lines running to it and an electrical connection running from it to the clutch.] As most of the vacuum lines are shot on this car, I'd kind of like to convert it to electrical operation/control.

Any thoughts on where to start? Anyone done this before?

Never seen one controlled by vacuum, all I’ve worked with simply used one 12V+ wire. I thought diesel didn’t make vacuum anyway?
Switching to a different compressor will involve a custom mount. Not all that easy unless you have a welder and a bunch of tools. The hose fittings may be the same, but I doubt it. I put a compressor from a Toyota Tercel on my Chevy V8 a few years ago. I made the mount from scratch, and installed new –AN fittings on everything. I also did the same on my ’91 Toy 4X with a 4cy. I like the Tercel setup and a complete system from my local junkyard is $85, and as a bonus they have ½ price days now and then.

The early 123 automatic climate control system (through'79) did indeed have a Chrysler servo system and I think there are some vacuum components. This is an EXTREMELY difficult to rebuild climate control system.

That said, this has little to do with the compressor, only the climate control (automatic temperature control) function. I'm pretty sure that your car has a two cylinder York type compressor. You do not state what your goal in "upgrading" is. Regardless of the compressor, your biggest problem will most likely be the servo climate control system.

Assuming that you want to change from the York compressor so that you don't have to use R12 would be false economy. Your York is probably in good shape and if not, a quality rebuilt can be had for $100. That's very cheap in "compressor dollars." Since R12 prices are going down, you can get it for about $15 a pound or so. To convert to a different compressor would cost hundreds and hundreds of dollars. Not an economical endeavor just to replace $15 refrigerant with $6 refrigerant.

The refrigerant, even R12 is probably, by far, the cheapest component in your a/c system, certainly in your Chrysler Servo control system.

Good luck,

there are rebuilt A/C servos available for $300 for that car. The engine driven vacuum pump has to work also (to work the door locks, engine shut off, and all the other HVAC damper doors.

That system is EXTREMELY costly and difficult to restore to good working condition if in poor condition now. All the vacuum ;motors' on the heaver/ac box will need checking and probably replacing, the servo controller, and of course the refrigerant system itself. The 'servo' switched the doors and modulateds the amount of hot water going through the heater core to control the temp.

You guys make that sound really scarry $$$ wise. I can see why dokhans want's a different (normal) type on there. What a strange setup.....

Btw, I know some will disagree, but I've converted at least 6 different (none MB) from R12 to 134. Two I flushed out the original oil first and added the "134 oil", the others I just added a bit of new oil to comp the losses. The first was probably 6 years ago, so far no problems. I looked at it like this: There's no way I'm changin all those seals n stuff, so this will either work, or it won't. As I suspected, the rumors about seals, oils and whatever else needed for the conversion was just a scam generated by those who sell the stuff.

Here is one that looks like it has been converted to a different compressor than the original York.

300D on ebay

__________________
Jim

Although they both function to provide air conditioning, there are two almost separate issues here.

First is the climate control itself, second is the refrigeration portion. Regardless of what climate control system, Chrysler servo or otherwise, you still have a refrigeration system to fix. The servo control system has nothing to do with whether or not you convert.

As I said before, it would be much cheaper and give much better a/c to just fix whatever you need to fix in the refrigeration portion and stay with R12.

In the case of the Chrysler servo system, the refrigeration portion is the least of your problems.

Best of luck,