Another heater problem in 300td climat control
 

I know there has been a lot of discussion about how to fix the climate control already but I have a few questions. I replaced the brushed on the motor hoping to get the blower working only to discover that the wire that connects to it has no voltage or very low voltage ( ~.02- ~.5v). After reading some of the posts here I found out about the temperature controller. The symptom I have now is that the blower will work intermittently and the air is sometimes warm and sometimes cold no matter how I adjust the temperature wheel. From this I conclude the following:
1. the motor is repaired (I tested it after I put in the new brushes)
1. the fan switch is good because the blower works sometimes.
2. the vacuum buttons work since I can see the actuators move and hear them when I press the buttons.
3. the heater core must OK since warm air comes out sometimes.

My question is what about the temp. controller box? Are the symptoms I have described characteristic of a dying temp. control unit (bosch 1 147 328 029)? I pulled off the cover and it has a few ICs and tranisters that could have blown from the blower motor being stuck when the brushes wore out.

Also the AC compressor is missing and the #8 fuse will blow when I turn on the ignition. These I would assume are not related to the problem I have with the blower motor working intermittently and intermittent hot air.

What should I try next to pinpoint the problem(s). Should I shell out the $80.00 to buy a new temp. controller?

The blower motor controller gives power to the blower. Not sure on your car but the following apply to my SD: Its part # 147-328-026, its to the left of the blower, the controller gets its power from pin 11 and then tells the fan which speed to blow. Hope that helps

Thanks for the advice.
There are two boxes attached to the underside of the dash, one is silver and one is black. The silver one is the temp. controller part no. 1147328026 but I am not sure what the other black box does, is this the amplifier? How do I know which if any is bad? The blower worked when I first started the car today. But it only works if I have the defrost vent on with either the black fan or white fan selected or with the white fan selected and any other vent combination. The heat is lukewarm at best which makes me think that the vent to the heater core may not be opening fully or maybe the core is clogged. I can hear the electric water pump going but I don't know if it is pumping fully.

If your 300TD is a W123, the black box is the blower control module.

http://catalog.peachparts.com/ShopByVehicle.epc?q=1982-Mercedes--benz-300d-Climate--Control&yearid=1982%40%401982&makeid=63%40%40MERCEDES%2DBENZ%40%4063%40%40MERCEDES%2DBENZ%40%40X&mod elid=6190%40%40300D&catid=242213%40%40Climate+Control&subcatid=242297@@Blower+Regulator&mode=PA

on a 123, there is also the resistor group under the hood fore of the coolant reservoir. list at $318 from phil. check connections at junction.

http://img.eautopartscatalog.com/hir...300&height=300

Thanks for the replies.
I checked the black box at the parts store it costs $272.59 and is called the blower regulator. I checked the connections at the resistor group and they seem good but the back of the plug is missing. I would be satisfied if I could just be able to turn the fan on and off and control the vents, which is what it does now but if I press the wrong combination of buttons the blower stops completely and won't go again unless the car sits overnight. I just want heat on, heat off and to be able to see out the windshield when it rains here in the winter. I may try to hard wire the blower to the fan switch on the console by bypassing the electronic control modules and then trouble shoot the water works to see why there is only lukewarm air coming out. Seems like the vent buttons work on vacuum anyway so they should still operate the vents. There is no way I can afford to pay hundreds of dollars to get the blower working. For what they are these parts are way way over priced! I will have another go at it tonight.

The blower motor regulator controls fan speed. Thats the other black box under your dash.
If you bypass the blower regulator, your fan will be on full speed when the ignition is turned on. You would have to put an on/off switch in the line to have control over it.
Did you check the connections at the blower reg?

I only saw a silver box, which is the temperature controller and a black box about the same size next to it which I now know is the blower regulator. I didn't mess with it yet but I will see if the blower will come back on if I disconnect and reconnect the plug to it. I will also try the same with the resistor box under the hood. I would imagine that the controller to different speed settings by switching to a different resistor in the resistor box. It may switch to a dead resistor.

As for the heat only being lukewarm, the monovalve may be the culprit. It's easy to access, easy to bypass for testing purposes, easy and relatively inexpensive to replace. It is simply a solenoid with the current controlled by the temp wheel in your CCU. If you remove the solenoid (inside the monovalve), then the heat will be full tilt all the time. If you pull the solenoid and get max heat, then you know the monovalve is not functioning properly. Given that you do this and have heat, then the problem is either the monovalve is getting an electrical signal and does not open (a solenoid problem) or the monovalve is not getting an electrical signal (a CCU problem)

Won't that compromise the watertight integrity of the monovalve?

I searched for "monovalve" in the index of my trusty Haynes manual but it wasn't listed. Can you tell me where it is? I am going to order the factor service manual for the 1985 300TD Turbo Wagon but until I get my hands on it I will refer to the posts here.

Do a search for monovalve. lots and lots and lots and lots of info

Firewall, engine compartment side , just inboard of the battery.

Found the monovalve and unpluged it. I when the blower came on the air temp seemed much warmer. one interesting thing though when the elect. water pump was running I could hear a rattling or clicking noise coming from the monovalve. I will tear it apart later. At least I know how to make the air warm. The main problem is that the blower won't come on at all now. I pulled out the black box and opened it up and found a series of relays to control the blower at it 6 speeds. I did a crude test by pluging it back in with its cover removed and with a plastic pen forced the relays to the closed position one at a time. Each time the blower would run at a different speed when I forced the contacts together. It to has a four of ICs that could be blown. Is there any shop that will test the blower controller and the Temp. controller? At this point I think that one of them has a blown IC or transistor that is causing it to work sporadically. I guess it could also be the fan switch or a connection between it and the controller. I think it is safe to say that the resistor box is good since the blower did work at all the speeds when I forced the relays shut in the blower controller box.

Can someone explain to me what these resistors do in relation to the rest of the heat/fan/climate control system?

Thanks.