280se 4.5 1972 A/C fan knob

[pilotds]

Anyone know where to get a replacement a/c fan knob/electrical unit to replace one that quit working? It's the left knob on the AC panel that controls fan speed. I think my fan is still working and it is just the switch that is out.


Thanks,

Dan

[Grubeguy]

The unit is a simple rheostat - you can take it out and clean it with isopropol alcohol and a small brush.

[pilotds]

The rheostat was working well up until now. Is there a fuse that I can check to see if that is what is causing it not to turn on? Is there another fuse box on the 1972 280se 4.5 in the engine compartment? Or is there a way to test the rheostat or the connecting wires?

Thanks Grubeguy!

Dan

[E430_4Matic]

Originally Posted by pilotds

Is there a fuse that I can check to see if that is what is causing it not to turn on? Is there another fuse box on the 1972 280se 4.5 in the engine compartment?

One of the under hood fuse blocks contains two fuses. One fuse is for the a/c and the other is for the the auxiliary fan.

[pilotds]

Can anyone tell me where these under the hood fuse boxes are? I can't seem to locate it.

Thanks,

Dan

[E430_4Matic]

Dan, They're along the firewall. There's also a pair for the power windows and another pair for the radio and electric antenna.

[Ed Mclass]

The housing is about the size of a small matchbox and is on the left fender top under the hood area.

[pilotds]

Thank You everyone for your help. I found the fuses and it was indeed a blown fuse. The fan was blowing a fuse each time it hit a certain low fan speed so I took the rheostat out and took it apart and cleaned all of the contacts. Now the fan runs great and doesn't blow a fuse at any speed.

One question though. After running the fan for about 20 minutes and then taking the rheostat out, the rheostat itself was pretty hot. Is this a normal thing? I didn't run the fan and then taken out the rheostat after I had cleaned it to see if there still was a heat issue yet. Thanks for the help. This site is invaluable. And the 108/109 MB's are the best ever!!!

Dan

[E430_4Matic]

Dan, Like a dimmer switch that gets warm, I would think the heat build-up is normal to dissipate the unused current.

I have a question: After cleaning my blower switch with contact cleaner, it doesn't turn as smoothly so I'm wondering if there's a grease I can apply which won't interfere with electrical components.

[pilotds]

If you take the actual rheostat apart, like opening the metal prongs that hold it all together, you will see that there is one inner circle of metal where the contact is actually made for the electrical element and then a coil like perimeter around the diameter of the white part. This coil like texture is the resistance device that you feel when you rotate the knob. There is a piece of metal that touches the coil and creates the friction in the knob. What I did was used fine grit sandpaper to clean all of the metal contacts including the little piece that rubs against the coil. This loosened the resistance a little bit. You could even sand down the coil itself if you don't want to open up the metal prongs and take the whole thing apart. But don't sand it too much. Do a little and then try the resistance and make it uniform.


Hope this helps.

Dan