Automatic CC always hot!

[dieseldude]

A question for the experienced in the Climate Control world.

I have a W123 300D with the early servo-type CC system. Ever since I've owned it, it has only blown in the default full-heat mode. I know my compressor is locked up, so I'm not expecting AC, but I'd like to at least mix the scalding hot air with outside air for more comfortable heating.

The different fan settings (auto-lo, auto-hi, bi-level, def) all work with approriate changes in fan speed, though there is a 5-7 second delay on shut-off and start-up of any mode, save def.

Any ideas? Vaccumm leak I'm guessing, but I don't know where to start. I'm sure I'm not the only one who has experienced this

Thanks much in advance,
- Ryan

[mbdoc]

The most likely cause is a defective servo! & they can wipe-out the amplifier(control unit).

BY default do you mean DEFROST?? Does the blower come on when any of the buttons are pushed?
These cars have vacuum hose problems(A/C/C) next to the battery!!

[dieseldude]

Oh no, I meant 'default' in the heat-only aspect. The blower only comes on when one of the buttons is depressed (except the OFF button ) All the different function-buttons change the speed of the fan accordingly.

About the servo: I though that its tendency to fail was caused by warping and cracking of plastic shell where the elements could then find their way in. Mine is not cracked and I considered myself lucky - maybe I'm not.

How else could one tell if the servo's the culprit?

regards,
- Ryan