Replaced monovalve-now my AC has hot air mixed in - PeachParts Mercedes-Benz Forum

jpjp22 · #1 09-09-2009, 04:05 PM

I have a 1986 300SDL. I replaced a torn monovalve last night and now I have hot air mixing with the cold air. The only place it feels a little bit cool is in the left/right lower vents (not the one where part of the vent in a "fixed-vent" to blow on the windows).

I know there are hundreds of threads about A/C and heat but I was hoping someone might have quik fix or something to check.

This was bad timing as it's 95 degrees here in Dallas today. I had no heat last winter but it really only bothered me on one road trip. I thought I would go ahead and replace it but if I don't figure something else out pretty quick I will put the torn one back in until winter time.

rrgrassi · #2 09-09-2009, 04:57 PM

Was it a new or used monovalve?

jpjp22 · #3 09-09-2009, 05:35 PM

It was a new one. It was free to me since someone gave it to me. I can't remember if there was a brand name on the box. It seems llike it was blue and white. It was not Bosch. There was German writing on it though.

You think it may be bad?

Cr from Texas · #4 09-09-2009, 06:41 PM

I bought a set of 3 monovalve repair kits on ebay last year. None of them worked. I did save the rubber pieces to put on a Bosch unit that had a torn diaphram.

The test I used was: Use the top solenoid coil and insert the kit into it. Apply 12V and the valve should extend and stay extended (close). These stuttered in and out.

jpjp22 · #5 09-09-2009, 10:38 PM

Good idea... I'll have a look at the one I put in and maybe trade out the rubber diaphram to the original Bosch.

BTW, this one I put in says VENTIL EINSATZ (which is german for "valve insert"?) in a blue and white box. So it's apparently a noname brand.

#6 09-09-2009, 11:10 PM

Also, check the electrical connection on the monovalve. Last time mine started acting up, it turned out to be slightly loose connections. A little adjustment and some conductive "grease" solved the problem.

vlado · #7 09-09-2009, 11:38 PM

if you want quick fix you can always put shutoff valves on your heater hosess and shut them off thru summer,and open them thru winter

jpjp22 · #8 09-10-2009, 01:05 AM

Thanks guys for the additional input. I'll check into those things too. Looking at the old monovalve insert again tonight, it doesn't look like it would be a piece of cake (for my limited skills anyway) to take apart and put back together with an intact diaphram. I might as well take the old one apart anyway.

At least I know I will have cold AC again here in the next few days when I get time. I have another car I can drive in the meantime.

BTW, I bought another one of these things last week. (I must be catching the disease). It's a 1987 300SDL, same color interior and exterior but with about 237K miles. It has a few issues but for what I paid (dirt cheap), it's fine if it turns out to be a parts car. But I will have to start a new post about that car when I get the time.