I have a 1983 300SD. The blower motor isn't coming on, so I can't use the heat or AC. I checked the fuse for continuity and its fine. There is either high resistance or the circuit is open somewhere. Anybody have any ideas how I can diagnose the problem? Does anybody have electrical schematics?? Any help would be greatly appreciated.

Bench test the motor first, thats what i'd do.

how do you bench test the motor?

Remove it and shoot 12 vdc to it.....

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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

is there anything simpler. I'd rather not have to take it out and apply power to it. I'll do it, but I'm wondering if theres another alternative.

That's the first step. You don't need to remove it. There is a plug right on the outside of the housing where you can apply 12V and ground.

If the blower itself is not the culprit, then you've got a tougher task. The problems can be:

1) Blower controller
2) Blower resistors
3) CCU.

I lost the blower on the SD last winter. Took a month to finally resolve it. In my case it was the CCU.

you can try hitting it lightly, take a small hammer and hit it. Sometimes they lock up if it frees up just spray some lube on it and youll be good to go.

I had the exact same problem a few weeks ago!

What I have found was that if I press gently on the temperature dial the heater motor would suddenly start.So i removed the wood panel surrounding the heater controls and found that the heater unit itself was not secure properly behind the wood panel,and noticed that the dial wasn't sitting smack in the middle of where it should have been.
Put everything back in place and voilą! All done and all controls are in tip top shape!
Give it a try and good luck
Dan
Vancouver Canada

whats really strange is that out of nowhere the blower motor turns on. I'll be driving and it will intermittently go on then shut off. Where exactly is the plug in the housing where I can apply power and ground. Is it on the climate control panel?

Drop the passenger kick panel. The plug is readily apparent right beneath and forward of the blower.

Removed the panel underneath the glove compartment. Removed the wiring harness and applyed power. The blower motor came on which led me to believe that the brain to the blower is bad. Only problem is that the air is coming out of the vents near the windshield, not the front facing the passengers. When it intermittently came on, it came on out of the vents facing the passengers. Strange? I'll replace the blower motor brain tomorrow, but I don't want it coming out the vents near the windshield. Can anybody help me out??

If you do a search, you'll turn up more info about your CCU problems than you'll know what to do with.

Common problem area for our old cars and a lot has been written here.

Good luck with it!

Bill

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1998 E300 +310,000K
1996 E300 +460,000K