A/C compressor relay on '85 300D?
 

A/C compressor relay on '85 300D?
My buddy's got an '85 and can't get the A/C to run. Pressure switch and charge are good, cold air if he hot wires the compressor clutch. He's looking for a relay in the compressor circuit. Is there one? If so where? Other ideas?

Thanks.
Fred

...oh yeah, I want to help him out because he just donated a good used trans to get me back on the road. I'll do the manual conversion next time! fmb

Check another
 

Check the relay in the front of the engine by upper radiator hose/thermostat. should have three poles 1 single and 1 double. Pull the connector of the single pole and see if the compressor kicks on - if yes replace relay

My '85 has a Klima
 

Look for a large, black relay just forward of the fuse cover. MB started putting the Klima relays in the '85 models. This relay looks at several parameters, then decides whether the A/C clutch should engage. Mostly engine speed and temperature in '85, I think, but later models also checked compressor rpm and other things.

Mine has the word "Klima" embossed on the cover.

The relay and related circuit board are repairable. Mine was inop when I got the car. I popped the cover off, found a large transistor on the board flopping back and forth because of broken solder joints. I resoldered the leads and it has worked fine ever since. Pray he doesn't need a new one (shudder). They are pricey.

i have a 85 300D and have been down this same road, mine had a land burnt off the circuit board, i used some small guage wire and repaired it, using a small 25 watt pencil soldering iron. everything is working fine now. however,,,, i had already ordered a new relay from mercedes, they wouldnt return it because it was a special ordered part. if you need a new one, i will sell it at a discounted price.

Thanks guys. As soon as he gets back in town we'll have a look for the relay and see what we find. Matt, I'll let you know once we find out what we're up against. A/C hardly seems an issue at the moment...raining again (14th weekend in a row). While I'm swapping the trans in my car maybe I'll play Monster Garage and add a bushhog for the yard...the poor old cub cadet is struggling to keep up...

Fred