Hey everyone!
I've been away a little and did get feed back on my old post, but I do not think I asked the question right. My problem is that on my 87' 300E fuse 7 blows when I turn on heat/AC. It does not blow right away though. If I am sitting in park it will blow air for about 15 to 20 seconds. I am not sure if it will adjust with the temperature settings or not. If I am driving and I turn on the defroster it blows nice hot air out of the defrost zone. I can then switch to a different setting and this changes. I again do not know if it will blow hot or cold air based on the settings. I then come to a stop at say a stop sign or such and the fuse will blow. When the fuse is blown it kicks out hot air continuously. The greater the intensity as I drive faster. My back up lights do not work when fuse seven is blown. I have heard the problem might be with the monovalve, but I would not know how to check it, because I don't know where to find it. If anyone has had this type of problem or can give me a few tips on where the problem may be it would be greatfully appreciated. Another problem I have is that when the front doors are open the light on top will not go on automaticly even when it is set to do such. And the safety seatbelt light up on the roof does not go on as well. This may be related but I am not sure. I also heard the problem may be with a short in the electric system. Is that a possiblity?

The whole situation arose during the summer while I was driving down the highway (around 20 miles). The windows were down and the A/C was probably on high. When I reached my destination all of a sudden I heard a noise and the heat came blasting out.

If anyone has encoutered such a problem or has insight on how to correct the problem it would be nice. I do not have much money to see an auto machanic and do not wish to if possible. I believe I have been "screwed over" by one and would like to know more of where the problem is so I don't have to spend money on labor for "finding" the problem.

Thanks for all help! Please provide details to where items such as the monovalve are located and/or picture so I have an idea to reference from. Thanks!

I will be introducing my car shortly!

Brian

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'87 300E 69K miles
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the brake lamp still works?

seems it got short circuit.

 

All the break lights do appear to work when the fuse is blown. How would I go about finding where the short would be located. And if I had an automachanic do this what would you expect the price to be?

Thanks,
Brian

 

your problem needs further testing to locate the source.

the only thing that you can do is to disconnect/segregate the suspected components till the problem cease to appear.

here are the components that uses fuse 7:

duo valve
a/c control unit
fan for interior temp sensor
auxilliary fan pre-resistor relay
temperature switch for electromagnetic or auxilliary fan (which i suspect as the culprit because...when you stop the car, the temp rises and this thing kicks-in).

mechanics will charge you much for such simple problem.

 

is there an online guide to where these parts are located so I can check them? or how would I go about doing this? I have searched google.com and nothing is coming up about this.

thanks
brian

 

you just go directly to the component and disconnect them.