Heater Valve Solenoid Question
 

When should there be power to the solenoid valve? The electrical water pump and the solenoid share the same fuse #7 on my 1995 E300D. I checked and the fuse is good and there is power to the pump, when I plug the pump wires into the solenoid I can feel it working. So, if I have the ACC on max heat, fan engaged should there be power to the solenoid?
A little help here please...it's getting colder and I have no heat...yes, I'm in California and it's not that cold here but there is frost on the windshield that needs to be removed so I can see. Thanks

I think the heater solenoid (monovalve) is a fail ON device, so removing power opens the valve, and applying power closes it.

That way if the power fails, you will have HEAT! :D

Hmmm, thanks Jim H, that design would make sense but the problem is that I do not get any heat, blower motor works great, and the solenoid is functional. since posting I have put a nylon spacer inside the top of the solenoid housing to extend the brass plunger valve 6mm and now I have heat. so, it seems that there may be something else wrong...ACC maybe? When I removed the solenoid and applied 12 volts the solenoid extended the brass valve about 6mm. When unplugged it retracted. I wonder if the pump and the solenoid/valve are powered at the same time?
I would like to fix this but haven't a clue.

I think the auxiliary pump runs anytime the ACC is in Auto and it varies the monovalve's Open/Close duty cycle to modulate the amount of heat produced to keep the cabin at the desired temperature.

I think the auxiliary pump runs and the valve also modulates in cooling mode to provide re-heat for better temperature control than just cycling the compressor.

So, I think the aux pump should always be running (constant voltage) and the monovalve is intermittent, so you would see voltage in some ON/OFF/ON/OFF combination.

Thx Jim, I'll guess I'll take the spacer out and connect a volt meter to the solenoid and wait to see if there is any ON/OFF cycling.