Weird AC behavior (1995 E420) - cold->warm->cold
 

I've just noticed this with my E420.

Whenever I start my A/C (be it in Auto, low or high fan speed, at any temp) the A/C would cool down nicely for a bit and then for a moment it would only blow warm air out of the vents until I move a little bit then it would start blowing cold air. After that no matter what I do (stop and go or normal driving) the air would be nice and cold.

I'm gonna check my aux. fan relays' fuses.

Any other ideas?

The warm air started coming after what feels like the A/C compressor shutting off.

It might be your Mono Valve, they go bad with time and easy to rebuild. Fastlane sells a rebuild kit for it.
Keep us posted.

When you first turn on the A/C, go outside and see if the low speed fan is coming on. If it isn't, the compressor will shut off after a bit. Once you are moving, you get airflow, and all is cool (so to speak). I am guessing that once you have warmed up a bit, the high speed fan is coming on at the stop lights to take care of engine cooling, so you never know for sure if the low speed ever came on in the first place.
Anyway... Check to see if the quieter of the two fans comes on when you turn on the A/C. If it doesn't you will want to check the relay, and if its ok, then check out the rheostat down by the ignition coils. (Its the little metal box with metal springs inside) Mine happen to have a corroded connection there...repairing it helped me keep my cool (so to speak).

Hope this helps...

-Larry

You should check the cabin temp sensor hose. Remove the glove box and look for a foam hose that runs horizontally behind the glove box toward the center of the dash where the temp sensor is.

The original foam hose disintegrates and disappears. Get some foam pipe insulation from Home Depot, cut to length and slip into place.

Good luck,

In the E420, that sensor would be overhead, where the sunroof and domelight controls are.

I took the car in for service and they diagnosed it as a faulty viscous fan clutch.. we'll see what happens from there on.

got the car back and they replaced the fan clutch. I don't think it had anything to do with the A/C cutting off. But the fan was making some noise last time. That's ok... $500 part on them.

They told me to come back next week because of a special ordered part (probably the aux. fan low speed relay).

The low speed fan(s) definitely are not working.

I can't find it in Fastlane either. I guess I'll wait for them to replace it.