I'm trying to get my ACC back in order. Today I installed a fixed climate control unit. The previous one got burned by a faulty aux pump and the ACC only blew hot air regardless of temp setting. To be sure that this doesn't happen again I unplugged the electric wire from the aux pump - I don't need it anyway.
Now the climate control behaves a little different - it blows ice cold air but only when the temperature wheel is set to the "MIN" (click) position. If I "unclick" it the ACC starts blowing luke warm, then very hot air again. It blows cold only on MIN.
could this have something to do with the inside temperature sensor? Could unplugging the aux pump have caused the sensor to switch off as well?

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1987 300E 185k miles

It is not the fault of unplugging the aux pump, I have unplugged many of them.

It could easily be a bad temp sensor as moving off the min position places the unit in the discretionary mode. In other words it looks at sensor values and temp wheel position to decide on heater control (or mixing).

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

thanks. I can't seem to find any information about the cabin temp sensor. AFAIK it's located next to the front cabin lighting. I have searched for it in an on-line MB parts catalog but the only related thing I could find was a blower motor for temp sensor. Is the blower integrated with the temp sensor? There also another ACC temp sensor, but it's located on the engine manifold so I presume it's a different story? which one should I be looking at to fix my problem?

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1987 300E 185k miles

Call Phil or Roy and ask if the motor and sensor are integrated. They are on my car.

You check the motor by putting a 1cm x 1cm piece of paper on the intake, and seeing if it sticks.

Mine was full of dust. Cleaning it out made a huge difference in the temperature regulation.

thanks. I'll carry out the "paper test" today :-)
is it possible that the blower works but the temp sensor is dead?

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1987 300E 185k miles

the paper test has proven that the blower is OK. what now? does anyone know if a dead temp sensor would be giving a high or low cabin temperature reading to the CCU? in other words, without the correct temp reading, would the ACC blow hot or cold air by default?

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1987 300E 185k miles