84 Mercedes 380SL too cold

[jpl]

I have a 1984 Mercedes 380SL (U.S. model). It still running R12. With the A/C on for more than about 20 min the evaporator freezes. No condensate drips from the drain tubes until the car has been shut down for about 10 minutes then there is quite a stream on the ground. The compressor does not cycle, it runs continuously. I figured that it was the ETR sensor/switch that is supposed to shut down the compressor when the evaporator gets too cold. Being an inexpensive part I replaced it and still have the same problem. I checked the old one by putting the sensor tube in the freezer and within 15 seconds the switch clicked. I took the sensor tube out of the freezer and within the same amount of time clicked again so there was nothing wrong with original ETR. I measured how much of the old sensor tube was inserted into the evaporator housing and inserted the same length of tube from the new one. If I disconnect the wires to the ETR the compressor clutch disengages which leads me to believe that the sensor tube is not properly sensing the evaporator temperature. Seems like a simple push the sensor tube through the hole in the evaporator case, the end.

Any idea what I am missing?

[bohica2xo]

The sensing bulb must make firm, mechanical contact with the actual evaporator. If it is just swinging in the breeze near it, the evaporator can reach freezing without the bulb sensing it.

[jpl]

Thanks for the tip. It is definitely not engaged in the evaporator. I will try to insert at a different angle.

[bohica2xo]

Poking around at an evaporator is not the best plan.

Go here:
http://eautorepair.net/Marketing/Default.asp

Spend the 20 bucks for a one month subscription to the complete Factory Service Manual. Find out exactly how and where the sensing bulb gets installed.

[jpl]

bohica2xo was spot on. I removed the blower motor and inserted the capillary tube into the evaporator and the compressor cycles normally.