Defroster comes on in the morning - can't shut off - air recirculation switch clicks
 

Weird problem has started in Klaus (1987 300TD) - within the past 3 weeks. In the morning the defroster comes on at a medium speed (not the normal high hurricane speed) - after about 20-30 minutes of driving, the air recirculation switch starts to click on and off (in an irregular manor) and then eventually the fan shuts off and the blinking / clicking stops. Sometimes it will start again, usually when I stop at a light. AFter the heater shuts off I can use all of the temp and fan controls normally (they will not work prior to this episode). Happens every day, morning and afternoon.

Additionally - last week I was in slow traffic, in the rain, and I had the defroster on (to clear fog from my winshield) - and I had to blow my horn. When I did, the blower motor shut off - then restarted after I let off the horn.

My monowiper also is running slow.

The glow plug lamp only comes on 50% of the time.

Hmmmm - as I am typing this, I am starting to think I have an electrical problem (maybe the alternator)?

I have a brand new, big battery, car always starts quickly.

Any ideas out there? I did jsut search on the blinking air recirculation light, but the symptom was different (blinking in a regulair interval - and that it was associated with code testing).

Hmm that is very interesting. I suspect a ground problem. Behind the gauge cluster is the mother of all ground points that covers most everything in the drivers area of the car.

Do you have the wiring diagram? If not go to w124-zone.com and download it.

If it was my car I would pick one problem and attack it, it might lead you to the causes of the other problems. If it is repeatable, I would go for the "honking horn kills the blower" problem.

Remember that the blower controller has the ground for the blower motor. Both motor leads go to the blower controller. However if something is wrong with the PBU ground, that might cause the reference signal from the PBU to the blower controller to go to zero, which would tell the blower controller to stop the blower.

If your car has a build date of 9/87 or later it has an updated PBU with blink diagnostics via the recirculation light. Or someone might have swapped in a later PBU. The blink codes are in the FSM.

Thanks jay_bob - I'll go take a look at my body tag during lunch and see what the build date is. If it is post 9/87 then I'll readup on using the PBU blink diagnosticts.

If your build is older it is entirely possible someone has swapped in a newer PBU in your car.

Problem solved.

I swapped out the climate control panel (I assume that is what it is called, it has all of the push buttons for selecting fan speed, etc) with one I had on the shelf, took care of the problem, and now all of my fan buttons and directions work again.

I had the console apart while I was installing my XM radio, the key was on but the engine was no running, I suddenly heard the clicking sound and heard what sounded like a vent being rapidly opened and closed (really fast). For the heck off of it I turned the temperature dial and the noise stopped, but it couldn't get it took start again. All during the life of this problem, none of my climate control buttons worked at all, that's why I decided to try replacing it.


Now onto the rest of my list.


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I checked, both of my wagons were made in February of 1987.


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