380sl monovalve - PeachParts Mercedes-Benz Forum

John_Winslow · #1 09-28-2006, 02:09 PM

I have a 1983 380sl based in the UK and am experiencing problems with the heater. I get only hot air in the footwells with no way of turing it off. I have read through the forum and deduced the most likely problem is the monovalve which looks easy to repair.

My problem is i cant find it. The images on other posts show it to be on the firewall passenger side. It isn't on either side on my car. The battery is close up to the firewall on the passenger side and a black cylinder of some kind measuring about 8 inches diameter is on the driver side.

I am beginning to get extremely frustrated and would be grateful of any guidance.

Many thanks

Walrus · #2 09-28-2006, 06:20 PM

John,

I believe you do not have the monovalve, but instead have the dreaded Servo controller/temp regulator (commonly called servo valve). The device you are looking for has a trapezoidal head on it, with both electrical and vacuum running to it. It should be located right next to the auxillary water pump. All this assuming you have the Climate Control II system

cbdo · #3 09-28-2006, 09:57 PM

Either of these assumes that you've got automatic climate control. The monovalve system has a horizontal row of pushbuttons; the earlier servo system has a vertical row of pushbuttons. If you've got a different system that doesn't have a thermostat setting the temperature for automatic control, you've got the European manual system that was never sold in the US, and most of us Yanks won't know what you need.

Strife · #4 09-28-2006, 10:03 PM

If you have the "II" system with the servo control, look carefully at the top of the SL forum for a modern, better designed functional replacement. Everything I've read while researching what model to buy says (1) the MB servo will certainly fail; (2) chances of getting one used that works at all or for more than a week approach zero; (3) rebuilds, not cheap in themselves, don't last either due to the limitations of the awful (Chrysler?) design. Me, I'd build the price of the above into what I'd pay for a used car with this system.

Everything I've read about the modern replacement has been positive, and puts the problem to bed.

Walrus · #5 09-28-2006, 10:11 PM

Quote:

Originally Posted by cbdo

...If you've got a different system that doesn't have a thermostat setting the temperature for automatic control, you've got the European manual system that was never sold in the US, and most of us Yanks won't know what you need...

Damn shame we wern't offered this option, in some ways.

Good point on designation of the systems. Climate Control II, vertical pushbuttons and temp wheel. Climate Control III, horizontal pushbuttons and temp wheel (After 1982 I believe). Addition in 1986 or '87 was a recirculation switch... More complications!

John_Winslow · #6 09-29-2006, 07:41 AM

Thanks all, for your help. I shall endeavour to find out which it is that i have.

The consol has 4 levers that move up and down vertically and a centre twist knob to marked I, II, III, DEF.

John

page62 · #7 09-29-2006, 08:54 AM

Quote:

Originally Posted by John_Winslow

Thanks all, for your help. I shall endeavour to find out which it is that i have.

The consol has 4 levers that move up and down vertically and a centre twist knob to marked I, II, III, DEF.

John

That sounds like the manual system. No servo (thank goodness...) You'll only find it in gray-market cars over here.

Walrus · #8 09-29-2006, 09:50 AM

Quote:

Originally Posted by John_Winslow

Thanks all, for your help. I shall endeavour to find out which it is that i have.

The consol has 4 levers that move up and down vertically and a centre twist knob to marked I, II, III, DEF.

John

Your system uses a vacuum pod to open the water valve (a valve similar to the valve used on a lot of chrysler, eg, products) and a set of switches to electricall operate a couple of other vacuum pods as well. Chances are the water valve has either been manually opened, or is otherwise faulty. In your case, at leat the system is much easier in some ways to work on. If you do not have the MB service manual (at least on CD), I recommend you acquire on ASAP. For those of us in the states, the CD is available from MBUSA Classic Center for around 20bucks US. All three systems are illustrated fairly well in that manual/CD.

John_Winslow · #9 09-29-2006, 10:46 AM

Thanks again both.

Walrus....I will get hold of a manual before i go too much further. In the mean time where abouts is the water valve located? When you mentioned it may have been manually turned off it rang a couple of alarm bells.

I know before i had it there was a problem with overheating. If the valve was turned off to direct only hot air inside the car thus taking it away from the engine wouldn.t that have been a simple fix to that problem?

John

Walrus · #10 09-29-2006, 09:57 PM

Quote:

Originally Posted by John_Winslow

Thanks again both.

Walrus....I will get hold of a manual before i go too much further. In the mean time where abouts is the water valve located? When you mentioned it may have been manually turned off it rang a couple of alarm bells.

I know before i had it there was a problem with overheating. If the valve was turned off to direct only hot air inside the car thus taking it away from the engine wouldn.t that have been a simple fix to that problem?

John

It's possible.

There were at least two variations of the manual system in the 107. The older or version 1 used a push/pull vacuum pod (two diaphragms), while the later or version 2 used a single-action with a spring. I believe in the 2nd version, the valve defaults to open, allowing water to flow to the heater core when there is no vacuum (line pulled or system non-functioning).

To find your valve, follow the heater hoses toward the firewall. It is probably mounted on the firewall.