Climate control - PeachParts Mercedes-Benz Forum

hitwtom · #1 02-14-2007, 10:14 AM

I've searched previous threads before posting, so here's my question. My heater works fine most of the time, however at random times it won't come on at all (blower). I saw in one of the other posts that it could be the ignition switch? Reading other climate control issues (circuit board repair and vacuum problems, I'm inclined to check out the switch first since when the system works, it works fine. This seems to be a very intermittent problem even though I'v only had the car for about a month now. Any ideas, suggestions? Thanks in advance. Oh yea, it's a 1982 300D Turbo.

SD Blue · #2 02-14-2007, 11:15 AM

On the thermostat housing is a temp sensor and the wire is usually routed in front of the valve cover. Check for a good connection there as this sensor is what keeps the fan from blowing until the coolant comes up to temp.(keeps the ACC system from blowing cold air)

MB-Owner-in-ind · #3 02-14-2007, 02:16 PM

There is a known problem with the electrical brushes in the blower motor. I haven't replaced any yet so can't tell you where to get them. I have looked at a motor and they are easy to get to. I have been told you can get them at a hardware store but I have never looked for them there. You can check your brushes without taking them out if the motor will start after you tap the housing. Otherwise it requires removal to check them (they will be very short if bad) and you might as well replace them because you just didd the worst part of the problem.

Biodiesel300TD · #4 02-14-2007, 02:38 PM

If it's intermitten I would put my money on an electrical problem. It could be the circuit board for the climate control unit. If you pull the CCU and take it apart so you can see the circuit board look for a burned solder joint. That could be your problem.

Jeremy5848 · #5 02-14-2007, 03:27 PM

Some posters have reported success in getting the fan to start by whacking the underside of the fan housing with a blunt object. Such a procedure (if it is successful) also confirms failing brushes.

Hardware store brushes have been successfully used by others. When I took my fan apart, I found that the commutator was so worn down that I had to replace the entire motor.

firstdiesel · #6 02-14-2007, 03:44 PM

I have a '80 300TD and sometimes when the blower is intermittent I have narrowed it down by pressing the defrost button. In my car the buttons are vacumme

except "DEF" and "BI-LEVEL" which are forced electrically and they also turn on the compressor regardless of the compressor switch position. Thus defrosting the inside windows. If I cannot get the normal fan positions to work "HI" or "LOW" then I hit "DEF" and the fan comes on, which would allow you to check to see if it is internal in the fan or not. Mine is NOT an '82 and I am sure that they did away with the vac style button. It is just a suggestion to try to narrow your search of ideas.

Jeremy5848 · #7 02-14-2007, 03:53 PM

Yes, that is a good test. If the brushes are starting to make poor contact, sometimes hitting the motor with full voltage (which is what the Defrost button does) will get the fan to start. Once the fan has started, you can shift to another setting and the fan will continue to run at a lower speed even though it would not start at the lower speed. However, that is a temporary fix only.

firstdiesel · #8 02-14-2007, 04:05 PM

Quote:

Originally Posted by Jeremy5848

Yes, that is a good test. If the brushes are starting to make poor contact, sometimes hitting the motor with full voltage (which is what the Defrost button does) will get the fan to start. Once the fan has started, you can shift to another setting and the fan will continue to run at a lower speed even though it would not start at the lower speed. However, that is a temporary fix only.

Thanks Jeremy, I always figured it to be vacumme problem with the vacumme diaphram which closes the contact and not a fan problem

. I've got an extra fan I'm going to pull apart and see if I can find the brushes. It sure gets hot down here sometimes when the fan isn't working.

(Sorry to the northern folks, I feel your pain, I was at Cinncinati Intl. yesterday during the freezing rain!)

Biodiesel300TD · #9 02-14-2007, 04:19 PM

The fan isn't vacuum opperated. The vac operates the actuators determining which vent air will come out of.

firstdiesel · #10 02-14-2007, 04:27 PM

Quote:

Originally Posted by Biodiesel300TD

The fan isn't vacuum opperated. The vac operates the actuators determining which vent air will come out of.

Yes, that too. But, on a 1980 there is a rubber plug with, I think 6, vacumme lines that run from the back of the pushbuttons to three vacumme actuated electrical contacts (yellow with both vac and wiring coming from them)directly behind the pushbutton panel. The only reason I have seen this is that I had to replace the pushbutton assembly and was completely suprised to see that much vacumme back there. They also go to the vent actuators (pink and grey). I believe that when Mercedes went to the horizontal pushbuttons that they may all be electric. I am not sure.

Biodiesel300TD · #11 02-14-2007, 05:14 PM

The way the CCU works is to turns the electric signals from the puch buttons for which vents should be open or closed into a vacuum signal so the actuators work properly. So the connectos that hook up to the CCU have some wires associated with all the vac valve you are seeing behind the CCU. and some of the wires go elsewhere.

#12 02-14-2007, 06:42 PM

Quote:

Originally Posted by hitwtom

I've searched previous threads before posting, so here's my question. My heater works fine most of the time, however at random times it won't come on at all (blower). I saw in one of the other posts that it could be the ignition switch?

I had that ignition switch problem on my 300D. Mine was obvious because I could "fix" the problem by just wiggling the key back and forth a little. If messing with the key does not cause the blower to start, it may also be the push button unit or blower as discussed above.

tangofox007 · #13 02-14-2007, 07:44 PM

Quote:

Originally Posted by hitwtom

My heater works fine most of the time, however at random times it won't come on at all (blower).

That condition is very consistent with cracked solder joints in the CCU.

firstdiesel · #14 02-14-2007, 09:06 PM

I understand now thanks.

hitwtom · #15 02-15-2007, 09:14 AM

Thanks all, hopefully it will warm up some this weekend and I'll be able to tear into it and find the problem. I've got a new radio to put in so the dash is comming apart one way or another.