Defrost only, single speed fan in W126
 

Hey guys:

My brother's 86 300SDL as suddenly aquired a climate control problem. No floor heat, only windshield, and the fan doesn't change speed when you push the high or low buttons.

Is this a vacuum problem, a pushbutton control unit problem, or (ouch) a servo unit problem?

Onset shortly after the turbo was replaced (dealer, plugged trap oxidizer). Vacuum lines intact, but I've not yet checked for leaks.

All help greatly appreciated!

Peter

Good thing you don't have a servo unit
 

Greetings Peter,

You can rest assured that you don't have a servo problem, cause you don't have a servo unit on your car unless it's an '80 The monovalve came out in '81 and everything since then is controlled by it, heat qty. wise that is. If you are getting no fan air movement at all I'd be checking the fan resistor to see if perhaps it has gone out, but first check the fuse to see if it has blown for you. In some previous owner cars they installed a 10 amp fuse in place of the 25 amp and it didn't last very long under a load. Your blower fuse should be red in color if it is the right one installed. Hard to imagine that all the resistors (4 in all) would have gone out in your resistor group that controls fan speeds. Even if the fuse looks good, replace it and post back your results.


Charles

Hi Peter,I had a similar problem with my '80 so I'm not sure if it's the same.I changed my blower motor and when I went to test it it worked fine,the next day on my way to work it would only work on defrost(max heat and fan).After talking to a guy that specializes in euro a/c ,he told me to look for a vacuum leak in the last place I was messing with the car.When I put the lower dash trim in I must have pulled a vacuum connection 'almost' off,it took me about 10 minutes to find it.There must be a check valve to isolate the climate controls and locking system from the engine,tranny and brakes,because the only other thing affected was the locking system,would only work about 3 times instead of 10 times(normal).To make a long story short,try the locking system to see how many times it will cycle with the engine off,if it's normal then you probably don't have a vacuum leak.At least it's something easy to check:D Good luck.

Fixed -- replaced the 8A fuse for the PBC -- died of old age, was cracked.

Nice, cheap fix, took about two minutes.

Peter

Dear "PS":

About the fuse that you replaced on the PBC of the blower fan, where exactly is this fuse located and how can I easily access it? Is 8A the location, or is it the rating?

Thanks.

Robert:

8 amp is the rating of the fuse, don't remember which one it was, you can check on the fuse box cover. It is one of the ones in the fuse box by the brake booster.

Peter

Mine did this.. Get a wire coat hanger... Straighten it out... Make a small J shape at the end of the hook like a knitting needle. (You need two of these) On the instrument Panel... MPH... RPM... Gas.. Ect... on the two sides that make the wide V or obtuse angle part going down towards the bottom of the dash. About 1/3 way down on both sides... Slide or push the J hooked coat hangers in. SIMPLY pull on them, and the instrument panel will pull out. at the bottom on the back, there is a vaccum hose. Make sure its connected. Mine was not. It fixed the fan problems, opened the middle vent, made the economy gauge work, better gas mileage... Odd but true.. ill make a Youtube video.