Paul, hope things are going well. haven't heard from this post for a couple of days so I assume you figured it out. I just learned some info on my A/C Relay from this thread.... http://www.peachparts.com/shopforum/diesel-discussion/127447-trouble-shooting-switch-control-unit-post922550.html#post922550 and found out that the A/C Relay for our '85 300td is a more complex Klima relay that sits on the drivers side fender just infront of the fuse box and the brake booster. must be the first year for the Klima and the only year in the 123. my wiring diag doesn't mention it... hmmmm... anyway cheers and good luck
Scott

You know - I found the Klima relay there as well. Interesting. I thought the Klima began in the W124 - oh well. As far as I know the wiring diagram shows this little relay under the passenger side. But nothing resembling the little ice cube with a screw fixture is in there. I am going to move on and hold onto this relay incase one if its other applications gives out. Best wishes on your trouble shooting!

klima relays were common to go bad. take it apart and re-solder as needed.
you may need a magnifying glass.
on a 85 it should be located on the drivers inner fender next to the fuse box.
goodluck
been driving my 85 300d on a repaired klima relay for a few years now.

1) Check freon charge
2) check low pressure switch on drier
3) Check relay
4) check climate control switch
5) check ignition switch

Mine Must BE A Flakey Ignition Switch
 

LARRY WAS RIGHT. No A/c Blower - tap the key and VOILA - Blower is on. So Larry, you said ignition switch. Are you talking about this?

http://img.eautopartscatalog.com/live/M505032967.JPG

Is that a fairly easy job. I am a moderate DIYer.

Paul

inop. ac.
 

I just finished rebuilding my 84 TDT (with two ice cube relays), and transferred various hoses etc (relatively new) from my 85 TD (one ice cube relay) that has been retired, but is in my driveway. I have all electrical diagrams, and manuals, so I will revisit this thread tonight and see if I can help.

The intermittent unpredictable nature of the problem leads me to suspect something like Larry's ignition switch problem, or possibly with plug connections to the electronic climate control module, or maybe the ambient temp. sensor. I will check electrical diagrams tonight when I get home and get back.

Good luck,

Mark