How can I get the heater blower on at all times? - PeachParts Mercedes-Benz Forum

dieseldaddy · #1 12-04-2002, 04:03 PM

OK, I have been fighting with my 1981 300TD blower motor. I thought I "temporarily" fixed it about a month ago, but now it is not coming on at all.

Here is the scoop:
The heater works...but the BLOWER works only erradically. Does not work to jiggle the key, bang on lower dash panel by motor, etc. I think I have to actually repair something.
Once in a GREAT while, we will be driving and the blower will come on. For a second. I mean a second. THen it shuts back off.

First question: does the blower only come on when the A/C compressor is running? Strange, but that seems to be the only time it will kick on.
Next question: If the A/C compressor was going bad, would that affect the blower?? (I don't think it should...)

I have checked the pushbutton controls, and they are apparently OK, as it works just fine when the blower is actually on, and the blower motor/brushes seem fine too.

It is VERY cold now and my wife will not drive it until I get it fixed.
ANY SUGGESTIONS??

Thanks in advance!

Ken300D · #2 12-04-2002, 06:15 PM

My 1982 300D got to the point that the blower would only work in DEFROST mode, the far left button.

Solution: Took the pushbutton assembly out and resoldered every solder connection. Also took strips of heavy paper and cleaned the relay contacts. Verified relay contacts were getting cleaner by using an ohm meter.

Works perfectly now. Sometime in the past year I posted a series of pictures of pushbutton unit removal and disassembly.

Ken300D

#3 12-04-2002, 06:26 PM

It is possible that the engine block temp sensor that is on top of your thermostat housing is faulty and not allowing the fan to blow.

The senor is located on the top of the thermostat housing. Next to it is a temp sensor to activate or allow vacuum to the egr valve. This sensor has a thin wire going to it not vacuum hose.

To check it remove the wire from the sensor and ground it to the body of the car.... just use a loose wire to ground it. and IF the climate controls work then thats your problem.

Now if that is the problem you can temp fix it by grounding that wire to the body. but I would suggest getting the sensor replaced as cold are on the feet is no fun. also you dont want the fan going when your trying glow plug

bob c

#4 12-04-2002, 06:36 PM

Hi DieselDaddy.
It's Shawnster from Wausau WI, originally from Grand Rapids.
On top of the thermostat housing you will see the wire that The Bob is talking about. Right next to it is a thermovacuum valve with 2 vacuum fittings: one going to the EGR valve and one to the throttle linkage.
Be exceedingly careful: I took for granted that the fittings were metal (they're plastic!) and I accidentally cracked them off!
So, if you're poking around there be a little careful.

#5 12-04-2002, 07:18 PM

I second that. I broke mine off when I was drilling out a broken thermostat bolt, (That was not fun).

Which led me to blocking off my ERG valve. What an improvement.

bob c

MVK · #6 12-04-2002, 07:39 PM

Ok: First check out like Bob said- The temp sensor switch. If thats fine then you have a bad ACC.
The blower motor comes on always with AC on but not when AC is off. Is that right? Ok if thats the case its nothing wrong with the blower motor. Check the ACC panel solders etc.
Bad Carbon brushes on blower motor will give you a sporadically working blower even under AC mode so. I would start troubleshooting from ACC solders.

MVK

dieseldaddy · #7 12-04-2002, 08:20 PM

Thanks guys!

I will check the sensor...
One thing about the blower motor brushes...er...I think I was looking at the wrong thing.

Can someone please tell me where the brushes on the blower motor are? Are they just the same as the voltage regulator brushes? And how to get them off?
Thanks!!!!

#8 12-04-2002, 08:31 PM

Your symptoms sound a lot like those I had with my 78 300D two years ago. Turned out to be worn out brushes on the blower motor. Found some a a local hardware that fit after a little filing.
Just a thought.

#9 12-04-2002, 08:55 PM

I have had the same problem this year the couple of times I need heat. Didn't know about the switch, figured the monovalve was bad but now I will try the switch first.
Where are the brushes you ask. Drop the rt side kick panel and then take out the three or four screws holding the blower assembly in place. The motor is right in there and I guess there are two types, one you can fix and one you can't get into. On mine you could see where the brushes were. You bend 2 little tabs up and the brushes pop right out. You will have to cut the wires or desolder them. I found new ones that were very close at the local ACE hardware store. Any alternator or motor rebuild shop should have them as well. Just put them in place, bend the tabs back, and solder the connections.

SCOTTFISH · #10 12-12-2002, 08:47 AM

Could this be my problem of the blower blowing heat out but at a small amount? My car blows a little heat at the low fan speed and a little more in the high position, but overall it takes a good while to get warm inside on a cold day. I am used to the fan blowing hard at the high position to the point that after a few minutes, you are ready to cut the heat back. I have an 89 300 se. Can anyone help me with this?

Scott

#11 12-12-2002, 03:35 PM

Scottfish

When the brushes get badly worn the heater fan begins to slow down a lot. It can make all kinds of obscene noises, and it may only blow when jarred around a bit.
The brushes are soft metal and they are spring loaded to be pushed into the armature. When they wear they get shorter and shorter until they no longer reach. That is why the jarring can sometimes make them work.
Also the contact failure will cause the fan to blow with less force. The brush replacement should be a DIY job. I fouled up the first attempt by not getting the brush wires soldered on there correctly. You will need to pull the fan motor and it is not hard to pull apart. Just bend the tabs and it should come apart. Then at least on mine the brushes were mounted on the end plate assembly.

SCOTTFISH · #12 12-13-2002, 08:52 AM

Sounds like a fairly easy procedure. Can you give me some details of where they are and maybe some pictures of what they look like? Do you think the brushes are the problem? It does seems like at times, it does blow a little harder. Any details or directions to other threads for information would be greatly appreciated.

#13 12-13-2002, 12:42 PM

I tried to jump the heat switch and didn't do anything. I did learn to NOT stand barefoot on wet ground and grab a hot wire though

Peter I think said that if this didn't work then the problem was in the push button unit so I figured what the hell lets take a look at the guts of the thing. When I pulled it out it had a reman sticker dated 11/96 on the bottom. Inside all the copper traces had been gone over with solder. I just reflowed everything and hit all the pins where they came through the board. Not a hard job at all and took about 45 minutes start to finish. Best thing is the heat now works, fan blows when I want it to blow, and A/C is fine. I now get air flow in ways it has never worked before. It was kind of cool with heavy rain this AM and when I turned on the climate control it started mixing air going from floor to upper middle vents. Floor was warmer, centers were cooler. When it got to what I had set it to fan spun down to very low and cabin temp was perfect and stayed that way.

Credit this board with another $150.00 savings!