Hello All,
Got a new problem with my '84 300D. The heat is always on, no matter what position the ACC controls are in. About two weeks ago I drove away from the house and the heat just never turned off. It always ran a bit since the garage is quite cool before switching to AC but now full heat all the time.

-I have replaced the ACC (pushbutton control) with a new unit from GDL
-Monovalve removed, bench tested, seems to function normally, opens and closes repeatedly and seals when blown through. Was rebuilt a few years back.
-No voltage present on the Monovalve control wire with ACC temp wheel at 72 and the heat kicking.
-Visually checked fuses, all seems in order.

What next? The car is undriveable as it is.

Thanks, RT

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When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

Does the horn work?

Does the auxiliary fan work properly?

I had the same problem and I bought just the guts of the monovalve but it ended up being the whole monovalve that fixed it.

Hey Brian,
No horn does not work, just checked it. Auxiliary fan? Do you mean the heat/ac fan? Seems to be okay, just have it on "auto"

RT

__________________
When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

The auxiliary fan in front of the condenser does not work either.

Replace fuse 14.

Oh, THAT auxiliary fan! Feeling like a noob here....

So I checked fuse 14, pulled it out, put a meter on it, checks out fine. Swapped it with fuse 12. TADA! Everything now works normally. WTF, I did check all the fuses initially, and spun them in their mounts to make sure they were contacting well. Don't see how I missed it. The fuses are the "aluminum" kind. I have heard they suck, is that so? Use the copper versions?

I'm okay with replacing the ACC unit. That system would act up time to time, and shutting it down for a while would revive it, so I think it was due anyway.

So thanks Brian! I just spent $200 on a fuse! Not that I really give a crap, the car works again and thats all that really matters to me.

RT

__________________
When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

Yep, we've all done it once or twice. But, take heart..........the ACC probably needed replacement anyway.


The aluminum fuses are known to cause issues from time to time.

Help is what we do here.

I love this site! And, I love a CCU that doesn't always blow hot air even better. I only had to replace a fuse, thanks Peachparts you saved me again!

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1984 300D, 228k, Light Ivory, Java MB-Tex