Odd 1987 300SDL mono valve behavior - PeachParts Mercedes-Benz Forum

oilslick · #1 12-17-2017, 07:39 AM

Quote:

Originally Posted by Diseasel300

Unplug the monovalve and go for a drive. If you have full heat all the time, it's a control issue. If you have intermittent or random heat, the monovalve cartridge is bad. The SDL will heat fine with the Aux pump dead, so a failed one will not cause a lack of heat.

I’ve unplugged the Auxiliary Water Pump and the Monovalve and still get very little heat. I will be flushing the system first and pouring in new coolant (Zerex G-05). The car sat for quite some time so I may be fighting a partially plugged heater core. I’ve also chased down and resolved several electrical gremlins in the car in the two weeks that I’ve owned it. I will not be surprised at all to find that both the Auxiliary Water Pump and Monovalve are faulty.

oilslick · #2 12-17-2017, 10:12 AM

Quote:

Originally Posted by oilslick

I’ve unplugged the Auxiliary Water Pump and the Monovalve and still get very little heat.

Unplugging the Monovalve produces no change in the temperature of the air being discharged. Unplugging the Auxiliary Water Pump produces no change in the temperature of the air being discharged. Unplugging BOTH at the same time produces no change in the temperature of the air being discharged.