Ok I am at the end of my rope and seem to have reached a dead end. My auxiliary water pump is still good (replaced last year), rebuilt mono valve, just replaced the climate control unit with a remanufactured Programa unit, and last but not least just installed a remanufactured Programa temp. control unit.

The air is blowing through the proper vents depending on which button I press and if the fan is on auto the temp dial affects the fan speed. However I only get hot 140 degree air blowing through the vents no matter where I set the temp dial.

What have I over looked? Thanks for any suggestions.

Be well

I would start by checking the connection to the monovalve and the #14 fuse.

I have voltage at the mono valve and the fuse is good. My ohm meter is shot so I have not been able to check the wiring inside the mono valve. However the plunger unit is good.

1984 300d Turbo 145k
Check Your Heater Temp Sensor On Top Of Center Dash 2 Wire Plug
If Open Goes To Full Heat, New One This Site This In Series With
Temp Control Wheel

If you are getting voltage to the monovalve, it should be closing. I would double check the connection to the monovalve, if that's OK I would suspect the valve itself.

No so fast. The monovalve is regulated by a switched ground. The mere presence of voltage does not tell the whole story.

Good point, you really need to see voltage between the contacts, not voltage between one of the contacts and ground. I would probably just toss in a new monovalve anyway.

It is easy to test the monovalve by connecting it directly to the battery. It should "click" when power is applied and removed.
The connector itself is a likely culprit; the female portion tends to "flare" and not make good contact.

That might work too. I replaced my valve a little while ago when I starting occasionally getting a little burst of hot air when I first started the car in the summer. It seemed like the valve was sticking, it would blow hot for about 5 seconds than go back to AC. It would only do it once ever 10 or 20 times I started the car, so it was difficult to tell what was going on. Replacing the valve made the problem go away. It might have just been a loose connector, or the internal check valve might have been sticking occasionally. Anyway, if you're going to redo the whole system, why not do the valve too?

The problem with throwing money at a problem is that the problem is often still there after the money is gone.

The valve is pretty cheap, and it's 20 years old anyway. It sounds like he's already replaced just about everything else in the system.

Lots of good info. Where can I find a entire mono valve? I can find many sites for the plunger replacement but not the entire unit. However before going out and buying more parts will try a few of the thing suggested.

Many thanks

P.S. I am the 3 owner on this great car. Bought it with 192,000 and I now have 410,000. It has served me very well and plan on 500,000 plus. Just had to mention this!

Purchase from the buy parts tab above.

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83 SD

84 CD

I got a monovalve from my indy (who seems to be able to get just about anything in about one day). Try calling Phil, check the dealer, etc. The part number for the entire valve is "1 147 412 019" I don't remember the price, but I'm pretty sure it's under $200.