On my '85 300d, last night the blower started behaving oddly.

While the system was in DEF mode, it started varying speeds.

This morning again. Starts normally then after about 5-8 minutes begins to slow, then run at varying speeds, but gradually getting slower. Swtiching the system back to bi-level, and manually selecting the low blower motor setting for 10 seconds, then swtiching back to DEF seems to wake it up again for a while.

Is this a simple blower motor impending failure or something else? I have never had a blower motor fail this way.

Keep in mind this is DEF mode so the rest of the CC controls are not in play, just the blower, regulator and I guess there is that control box I never knew existed until recently?

TIA

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

Very simple to diagnose. Use a test light across the blower. If the light is constant on while on defrost. It's not the controls. Check blower brushes and binding in the bearings.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

There is a blower motor control box, however in defrost mode it should put the blower at full power bypassing much of the control box. If you are not hearing an abundance of clicking from the blower motor control box then I would presume that the control has engaged the proper relay for full speed and that the problem lies with the motor, easiest way is as funola suggests. I would pull the cover and try to spin the motor by hand, if you feel it binding up then bearings are toast or you've got an obstruction.

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Thanks, guys.

Last night it sounded normal to me. Tonight it is making some noises as it varies speed, what I would describe as binding.

Have not had a chance to investigate but now I am expecting it's simply the motor gone south.

If not I have a spare CCU... somewhere. (But no backup control box.)

Tks

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

The weather has remained in extreme cold here so I wasn't in any mood to troubleshoot (I have to work outside).

Took it to my wrench this morning and we changed out the blower motor. Problem is solved. Well apart from the fact that the spare motor I had is evidently older than the one that came out, and makes way more noise.

I don't like the fact that none of these motor assemblies seem to have a maker's name or part number. I find that odd.

__________________


Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22