Monovalve Question - PeachParts Mercedes-Benz Forum

#1 10-19-2005, 06:00 PM

I have searched several threads and remain confused. RE: 85 300Dt

If I disconnect the voltage on the monovalve it should remain open and pour max coolant into the heater core right? Or is it the other way 'round?

And if you have any good idea for quick testing functionality that I might have missed, I will definitely read.

Thanks

sixto · #2 10-20-2005, 02:02 AM

The monovalve closes the coolant feed to the heater core when energized. Unpowered/rest position is open. AFAIK it's a PWM or frequency valve.

Sixto
87 300SDL

Hit Man X · #3 10-20-2005, 03:13 AM

I'd remove those four screws and have a look... the one on my L had a torn diaphragm only.

#4 10-20-2005, 08:51 AM

Thanks. And if only a torn diaphragm, I still need the rebuild kit I assume. Or is there a simpler fix?

TX76513 · #5 10-20-2005, 08:59 AM

After summer it's not uncommon for them to stick closed. Just cleaning up the cylinder with some steel wool is sometimes all that's needed.

BioBens · #6 10-20-2005, 09:25 AM

Just replaced the valve in my 84 TDT. There was no apparent damage to the old one, but the new valve sure made a big difff -- especially considering the cost and ease of replacement.

Brian Carlton · #7 10-20-2005, 10:04 AM

Quote:

Originally Posted by sixto

The monovalve closes the coolant feed to the heater core when energized. Unpowered/rest position is open. AFAIK it's a PWM or frequency valve.

The interesting thing about this valve is that when the solenoid fails, the valve remains fully open and maximum heat is delivered.

But when the diaphragm fails, the valve fails to deliver any coolant, even with a working solenoid.

The logic of an unpowered valve (PBU calling for maximum heat because the occupant is freezing), failing to deliver coolant, escapes me.

#8 11-01-2005, 02:44 PM

Interesting. I will pull apart. Thanks for all the help. It's my GF's daily driver. So I hear about the lack of heat alot.

Pete Burton · #9 11-01-2005, 04:53 PM

hopefully for you, that can be fixed even without working on her car.

sailor15015 · #10 11-01-2005, 05:08 PM

If the monovalve is bad or sticking, will it blow the fuse? I have the same car and my next suspect on my mysteriously blowing fuse is the monovalve. I'm going to tear into it tonight to see what's up.

vwbuge · #11 11-01-2005, 07:15 PM

I rebuilt my monovlave last year with a cheapo one from Ebay. My problem still exists. I am assuming that the rebuild kit I got last year was junk. I have to get another and see if that cures it.

Be sure to get a quality rebuild kit.