Brrrr! 82 300SD Heater Motor goes kaput!

Hey gang! Thanks to Kaia and Mercedessource, we completed our journey from Boulder, CO back to Portland, ME in our just-puchased-that-evening 1982 300SD. We made the trip back to Maine in 34 hours flat, averaging 25 mpg. Thanks to your book(s), we diagnosed a clogged ALDA line heading from the intake to the sensor and wala, bugs no longer hit our back windshield as we crossed Iowa. The only thing, and only thing that really gave us trouble on the trip was, 3/4 way back, the heater motor just QUIT. The gentleman we bought the car from stated that he had replaced the 'control valves' - which I read as he replaced the push button array in the center console (which was confirmed by finding it half-bolted in). So! Driving, driving, driving, warm, hot air either fast or slow courtesy of the two buttons to the right of the air vent selectors, and then phsst. Nothing. Lots of warm hot air pushing through the heater core as we drive, but no fantastic motor action. I am suspect of a bad connection after seeing the other wiring work behind the center binnacle rather than failed brushes; hitting on the box doesn't cause anything to spring into action. Fuse 8 and 5 are in good health and work accordingly. Any advice on how to chase this and debug? I'd love to wire power directly to the motor to see if she spins. Not sure where this plug is, and/or what it looks like. Other than that she was hard starting in the cold, but armed with Kaia's help, we seem to be back on track. Many thanks! James F. Smith mohawkjames@gmail.com

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Questions and Answers

Chassis Model Number

W126

Congratulations

Hi James, congrats on a successful cross country trip. My 126 heater motor manual covers the info you seek, but I expect you are in a hurry to fix it. You are on the right track. Go after the motor first and try to power with 12 volts directly. It is located under the dash on the passenger side. Remove the under dash panels. YOu will see the blower motor and look for a two pin push on plug. Remove the plug and test. If the motor won't spin it could just be worn out brushes (which we supply with instructions). Good luck, Kent

Brrr! Brrr? Heater Motor NOT Dead, but not working normally!!

Hey gang, So! I finally hooked up a direct power line to the heater motor in my 1982 300SD turbo, and sure enough, the motor instantly whirred into life. Sooo....the motor is not dead.....where do I chase this from here? I broke out my test light, and with the climate control set on defrost with the HIGH fan switch selected, got the following: Pin #12 hot on the large relay, all others dead. Pin #4 hot on the fan-switch side of the climate control cluster An assortment of three pins hot on the temp-wheel side of the climate cluster I purposely grounded the wire running to the switch on the thermostat housing to eliminate that as a possibility. Which should I hunt for next? Replace the relay or (ugh) the climate cluster? Many thanks, James F. Smith mohawkjames@gmail.com

Heater motor spins w/current applied to the motor directly

BRRR

Hey James F. Smith, I have the exact same problem...did you find the cause? I puchased the heater manual and brushes from Mercedessource figuring that would do the trick...the brushes were well worn but replacing them did not cure the problem. I get a slight humm coming from under the dash where the motor/amplifier was sitting and it goes away when I hit the 0 or off button. The fan spins about 2-3 revolutions when I first hit the low/hi/auto button. does anyone know what is causing the motor to shut down? I have also tried this at normal opperating Temp too. Anyone Anyone??? This is my weekend car and I miss driving her...no defrost and cold wheather is a bad mix. Mike Waine

CLimate control

I replaced my climate control and bang! Everything worked. I dont know if it will work for you but I was having the same problems. James

Let there be Heat!

Hi All, I finally tracked down the bad component in my heating system, it was the blower speed regulator! I may have figured that out sooner if I had purchased the MB heater system CD-Rom as Kent had suggested, but being a glutton for punishment I threw parts at it until I found the correct one. I had read somewhere online that when the regulator goes bad the fan speed is just cut in half...NOT TRUE! in my case it went out totally. Relying on some incorrect information I kept over looking the blower regulator. In an effort to keep you from freezing your buns off and making the same mistakes I made, I will pass on to you the advise Kent gave me...Call 1 800 FOR MERC to get the factory CDs. Hope this helps anyone having similar heater issues. Mike W.

My fan does not work either

When I saw this thread I was excited but after calling for the cd-rom there were none available. I can get the motor to run hooking it to the battery charger, but not to the battery, this leads me to believe that there is a resister in there somewhere I don,t know about. Im in MN and in a couple weeks I'll need heat and defrost. M-Source is a great help in my quest to have the best 300sd I can have.

Fan motors in '78 300SD, '82 300SD and '82 300D TD

I have had problems in all three of my diesels with the fan motors. I tried replacing the brushes but the commutators in all three were so worn that new brushes did not work. I found the price of new fans outrageous (motor with fan installed) but then I found that the motors were available separately at a reasonable price. the only problem is removing the fan from the old motor and installing it on the new motor (I broke the first fan I tried to take off). Having some experience with plastics I decided to try warming the bottom of the fan up by placing it in boiling water. This worked like a charm. I got the fan off the old motor and onto the new one with no problems!