Where is the heater valve on my 1990 190e?

The heater valve is located under the leaf trap. Open the hood, and remove the plastic grille which sits on either side of the windshield wiper. Valve is on the passenger side and has a red vacuum pipe coming out of it.

See if it holds vacuum.

I have a web page which can help troubleshoot this system:

http://cacavas.com/mb/TTM.html

Good luck,

John Cacavas

Los Angeles, California

jcacavas@gmail.com