I need your advise on a Climate Control Problem on an 1986 560SL.
The problem is that the auto temp change in the cabin is very slow to respond. In other words it gets to hot before the system cuts the heat and it gets too cold before the heat comes back on.

I have replaced the monovalve and I had an extra temp control module that I exchanged but both give the same result. I replaced the foam tube for the sensor on the dash. I have also checked the resistance of both the dash sensor and the sensor in the hearter box both read about 15K @ 65-70 degrees.

Any suggestions? Could it be that the sensors have the correct resistance but are just slow to respond. I hooked up an LED light to the monovalve and can see the voltage coming on and off.

Dave
86 560SL

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Dave

Almost all of that type regulation is from the in-car temp sensor. Many times the "foam" hose that allows aspritation from the blower motor fails & then there isn't any air flow across the sensor.

Also a dash "cover" will cause that!!

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Thanks for the advise. But I have replaced the foam tube and the dash does not have a cover. Would you suggest changing the dash sensor?
Dave
86 560SL

__________________
Dave

Will smoke be PULLED into the sensor with the blower running?

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

I am not sure, I will check it this weekend. If smoke is pulled passed the sensor would this indicate a bad sensor?
Dave
86 560SL

__________________
Dave

No, the opposite.
Normally, air from the cabin is pulled past the sensor. If the hose is broken, or the aspirator fan is not working, there is no air flow over sensor and it will be slow to sense changes in cabin temperature, appearing to be 'lazy' as you observed.

Best Regards,
Jim

The climate control in my '86 300E acted just like that. It would blow hot, then cool, then hot. Eventually it seemed to even out a bit. After reading all these threads on the sampler blower, sensor, etc., I went out to the car to check it out.

First, I held a small strip of paper up to the sensor grill next to the front dome light. The suction of the sampler blower held the paper to the grill. I concluded the sampler blower and its tubing were good.

Next, I looked into the sensor grill. There was lint in the grill. I removed the lint with a toothpick. Using a small flashlight, I could then see the sensor element. It had a white fuzzy appearance. I decided that there might be some lint stuck to it. I took a can of spray cleaner-degreaser used for electronic parts cleaning and sprayed up into the grill. The sensor came out clean and it was a bright blue in color!

The climate control system functioned very well in a short drive test. It seemed to be over its hot - cool - hot cycling. Time will tell but I think the layer of lint on the sensor insulated it from the sampled air.

If you use this type of spray cleaner, be sure it say "safe for plastics" on it.

I had problems with intermittent hot/cold output from the climate control in my '88 260e and the problem turned out to be the thumbwheel for the temperature setting.

I think it wears out in time. Unfortuately, I could not find a source for a replacement pot and had to replace the entire pushbutton control unit.

DROEDER,

Any update or final solution to your climate control issue? I've got the same issue with my '88 300 SEL. I've replaced/checked the same things that you have and have also replaced the sampler motor, I'll be double checking the tube assy from the sampler motor to the temp sensor shortly.

Brgds,

BENZSTER

Thanks guys for all the good advise. Over the weekend I was able to fix my problem by reattaching the hose for the aspirator on to the heater box. I guess it was pulled off while checking out other issues.

Dave
86 560SL

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Dave