ncdave

Hot water thru wsw reservoir tubes, temp gauge ok, but no warm air thru heater. Had monovalve reworked today by authorized M-B service place. The old valve was toast but still no heat. Dealer said he cud trouble shoot and diagnosis but it wud be costly. Any ideas please?

btesar

If '91 works the same way as 87', disconnect the wire connector at the top of the mono valve. This should set the mono valve to full heat. If you do that and drive at rpm greater then 2k, you should get heat as long as you have the fan on. That should bypass the climate control unit from requesting heat altogether.

I'm sure others will correct me if the '91 changed.

ncdave

Thank you very much for the tip. I will give that a try, hopefully today. I see that u are a fellow Tar Heel. I live in Shelby, abt 40 miles west from Charlotte. Thank you for you help, Dave Rose

btesar

Dave - Any luck getting the heat to work by pulling the wire to the Monovalve?

Brian

ncdave

I get a little but not enough to to heat the car. Can feel some when in defrost mode only.