I have a 1982 300sd that i'm in the middle of fixing up. We'll to add to my list of things to do now I have a broken heater.For whatever reason last week the heater stopped blowing air(cold ,warm or hot) nothing ,nadda.The only thing the heater does is make a faint hissing sound when turned to full cold.Can someone please tell me where to begin.I have two manuals, one has the section torn out and the other dosen't really seem to talk much about my car whatsoever so there no help. Also I had my door locks die about a month ago (the pump tested fine). Could there be a link?Thanks in advance for any help.

I believe the door lock vaccuum system is seperate from main vaccuum system so it's probably a bad vaccuum pod. Listen when you lock the drivers door for the pump in the trunk and maybe for a hiss coming from one of the doors. I had my fan on my 81 sd stop cold turkey too. Look next to the main fuse box under the hood for a seperate little black fuse box. If you have one it has a 30 amp strip fuse that's most likely toast. Oh yeah just for the record, behind the soundwall in the engine bay on the left side kinda below the fuse box there is a little resistor pack I think is for the heater that looks like a cube with a bunch of coils. Make sure that you don't have any leaves or sticks down there 'cos they'll catch on fire while your driving.
http://www.peachparts.com/shopforum/showthread.php?t=118285&highlight=w126+fire

__________________
"spreading a trail of obnoxious where ever we go"
1981 300sd w/ 341,500 miles

http://www.wecrash.com/pics/ddda_banner.gif

I would suspect the blower motor brushes for your heater problem. www.**************.com sells a kit including replacement brushes and instructions. About $20, I believe.

Did the pump test fine in or out of the car? You may need to access the drivers door.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

Its not that the pump tested good , it's that a pump that I pulled from another 300sd didn't work either so I'm pretty sure they are both fine.

From what I understand, I would have had previous problems with the blower not working from time to time if the brushes were to blame.Is this true?

Find the electrical connector in the blower motor wiring. If you have power at the connector when the blower should be running, then the motor is the problem. If you don't have power, the problem is elsewhere. Or you could wire the motor directly and see if it runs.

O.K. then , one more question.Where is the blower motor located on a 1982 300sd?Thanks for all your help.

The motor should be under the dash on the passenger side. I have a 300D, so I don't know the exact details for the SD. But on the D, you have to remove the plastic kick panel under the dash.

THe connection that goes into the heater control has a (12 volt reading). But when I measure the connection comming out of the heater control there is no reading. Is this normal?Also, when I play with the controls there is some clicking and hissing sounds.

Apparently all it took was a little sauder on the board.