Intermittent blower motor function

[ds190]

My 91 300TE, new blower motor 5 years ago (brand unknown but not MB) to replace squealing original, the resistor assembly and pushbutton CCU are original, and vacuum pods & aspirator blower replaced 6 years ago with MB parts. The 30A strip fuse was replaced and contact surface cleaned recently at the start of the intermittent blower issue.

Sometimes the blower works, and sometimes not. When the blower does not run, it does not respond to any setting of the CCU including the default defrost setting. I disconnected the 3 wire plug (of the red/black/yellow line that runs from the resistor) at the connector near the brake booster. I measured over 12volts at the red wire pin out, and measured about 0.5 volts on the yellow wire pin out at all settings of the pushbutton unit. That indicates pushbutton CCU not working?

However, yesterday the blower worked as it should, and responded correctly for all pushbutton settings. I measured a range from about 1.5 to 9.5 volts on the yellow wire pin out, depending on which button was pushed, and of course 12v at the red pin out. That says pushbutton unit is working?

Today the blower does not work again.

Does this sound like a pushbutton CCU that has solder cracks that maybe expand or contract with the weather and therefore works or doesn’t work? That I now need to buy a rebuilt CCU?

Thanks for your input, ds.

[JamesDean]

ds,

The PBU should output a signal 0-9v which corresponds to blower speed. This signal is fed into the regulator and it in turn spins up/down the blower. I can't remember if 0v=full speed or 9v=full speed.

When its not working, I would measure that voltage and see what you are getting.

You might have a cold solder joint(s) on it, or maybe something else. Not really sure, just speculating.

Not sure if you would be interested but I would be happy to reflow and recap the PBU for you. I've done a few units, 126 and 201 related. I reflow my 90 300D's PBU as well. Figured I would offer.

If you are getting the expected voltage at the line to the regulator, then maybe it is your regulator?

[whunter]

Originally Posted by ds190

My 91 300TE, new blower motor 5 years ago (brand unknown but not MB) to replace squealing original, the resistor assembly and pushbutton CCU are original, and vacuum pods & aspirator blower replaced 6 years ago with MB parts. The 30A strip fuse was replaced and contact surface cleaned recently at the start of the intermittent blower issue.

Sometimes the blower works, and sometimes not. When the blower does not run, it does not respond to any setting of the CCU including the default defrost setting. I disconnected the 3 wire plug (of the red/black/yellow line that runs from the resistor) at the connector near the brake booster. I measured over 12volts at the red wire pin out, and measured about 0.5 volts on the yellow wire pin out at all settings of the pushbutton unit. That indicates pushbutton CCU not working?

However, yesterday the blower worked as it should, and responded correctly for all pushbutton settings. I measured a range from about 1.5 to 9.5 volts on the yellow wire pin out, depending on which button was pushed, and of course 12v at the red pin out. That says pushbutton unit is working?

Today the blower does not work again.

Does this sound like a pushbutton CCU that has solder cracks that maybe expand or contract with the weather and therefore works or doesn’t work? That I now need to buy a rebuilt CCU?

Thanks for your input, ds.

Since this is an unknown brand aftermarket blower motor, 5 years is about average to require lubrication.

Remove the blower cover.
Test spin the squirrel cage with your fingers.
If it is stiff or fails to spin free, the bushings need lubrication.
I suggest transmission fluid or sewing machine oil, and 3-5 minutes of exercise (running) between applications of oil.
If the issue remains or the push button control reaction and function are not smooth/consistent contact "JamesDean" for push button control service.


If there is NO blower issue, I suggest you contact "JamesDean" for push button control service.




.

[ds190]

JD, the full speed voltage is 9 volts.

While checking prices and part numbers to buy a rebuilt pushbutton CCU, I pulled mine out to double check the number, which was indeed 124 830 33 85. I unplugged it, cleaned the pins, plugged back in, and voila, it’s been working for a day now. That could be good luck or I merely repositioned bad Bosch cold soldered connections that will some day lose contact again.

I also found in my parts bin a unit 124 830 02 85, which came out of an early 124 car from a PnP and has a Celsius scale. If my CCU starts acting intermittently again, I will swap that one in and send mine to JamesDean to resolder.

FYI, rebuild units are priced from about $250 (auto****az) to $500, and I found a MB factory part for about $700.

Here’s a thread about using 33 85 and 02 85 in a 124 car:
Climate Controller Part number Question

[whunter]

Originally Posted by ds190

JD, the full speed voltage is 9 volts.

While checking prices and part numbers to buy a rebuilt pushbutton CCU, I pulled mine out to double check the number, which was indeed 124 830 33 85. I unplugged it, cleaned the pins, plugged back in, and voila, it’s been working for a day now. That could be good luck or I merely repositioned bad Bosch cold soldered connections that will some day lose contact again.

I also found in my parts bin a unit 124 830 02 85, which came out of an early 124 car from a PnP and has a Celsius scale. If my CCU starts acting intermittently again, I will swap that one in and send mine to JamesDean to resolder.

FYI, rebuild units are priced from about $250 (auto****az) to $500, and I found a MB factory part for about $700.

Here’s a thread about using 33 85 and 02 85 in a 124 car:
Climate Controller Part number Question

Happy it is resolved.

.