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!

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.