climate control problems-300SD

[RG5384]

on my w126 chassis 300SD i have run into an acc problem. WHen the car has been sitting out in the sun all day(even with a sunvisor) the blower will not engage unless i wiggle the buttons on the acc unit. I can wiggle whatever i please as long as i keep doing it. Once the car has cooled down, or whenever it hasn't been in the sun for a long time, the acc works great. I can wiggle it as much as i want and it will stay working(when the inside of car is cool or just midly warm). What on earth could this be? if you need more info feel free to ask me. Thanks for your help

R

[speedy300Dturbo]

Could be the AC switch assembly. They tend to bite the dust after 10 years or so. Try taking it apart and cleaning it.

[RG5384]

the only problem with that is the unit is only 2 years old! is the actuall switch assembly hard to get apart? getting it out isn't a problem but i don't want to completely break a 300 dollar part.
thanks for the speedy response!
R

[speedy300Dturbo]

I've never taken the AC control panel apart, but others have had some success doing it. Another thing to check is the AC temperature sensor on the dash.

[brightem]

I had a similar problem on my 82SD. After spending the day taking out the climate control unit and scratching my head, I figured out that the fuse in the fuse box wasn't making a good connection. There was a little bit of corrosion on the connecting points and I took a bit of steel wool and cleaned it good. And now it works fine. Surprising to me, because the problems I encounter with this car are never that simple. Oh well

[Ken300D]

Good tip on the fuse connection! I had a similar issue with the auxiliary cooling fan in front of the radiator. I took off the fuse cover and inspected the fuse, and it looked good - but the metal looked a little warped. After looking the second time, I decided to take the fuse out and inspect it closer, since I've never seen that type of fuse before. Well, it had blown right against the upper copper connector, not in the middle where you can see it plainly. Upon taking the fuse out the metal strip just fell apart. Replaced it, and the fan works great.

I have a similar issue with the blower motor at times. Right now, it always works in the left two climate control button positions. The operation is sporadic in the right two (which I use the most, and probably have been used the most).

My plan as time permits is to remove the switch assembly, clean it as best possible, and based on a tip received elsewhere on the board, resolder the connections to a PC board that may have cracked.

Your problem sounds similar - but I would check the fuse box connections first. If I get to the switch cleaning task before you, I'll let you know how it went and any tips learned.

Ken
'82 300D

[dieseldan]

I heard from a mercedes mechanic that the solder joints in the control unit crack and can be resoldered easily. The fuse problem can be prevented by applying a little grease or vaseline on the ends of the fuses. My old bug would always be cured of electrical problems by "spinning the fuses" from time to time.