Dreaded ACC question
 

The car in question is an '85 300DT.

The blower has been acting up....sometimes blowing hard and sometimes not at all. This up and down behavior happens in all button modes. So I took out the blower itself and cross referenced (installed it) in my TD which has the simpler design. Blower works fine with no dead spots.

Therefore, am I right in thinking that the message going to the blower is getting screwed up?

Where do I start?

Thanks

Don

Isn't the blower also controled somewhat by the crouton toaster in the engine compartment?

Might want to try swapping the ACC control modules and see if the problem follows it as well.

I'll wager a bet its the Climate control (push button ) module, there are tiny little relays that carry the full current gong to the blower and the contacts get dirty and fail to carry current, you can burnish them with some sandpaper (600 grit crocus cloth?)
Then there is the well known issue of the solder joints on the connector header on the side where the plugs goes on. With all the W123 cars you have I am surprised you haven't seen this problem b4. Resolder all joints and see if that doesn't fix it.
I have seen both of the above problems, as well as burned traces caused by a short that occurs when the brushes wear down to little nubs (there is a retrofit fuse kit for this). I bought a spare panel just for the purpose of substitution for this kind of problem in my W123's. The dreaded thing was underdesigned from the factory INHO.
Dieseldiehard
1971 220 (gas) 4-spd manual 106441
1979 300TD w/ ’85 turbo engine 295530
1983 300D 243280
1985 300TD 217300
1987 300D 258230

Another thing that can cause this (along with large temperature swings) is a dead foam hose to the aspriator motor for the interior temp sensor. It's behind the glove box. Replace with something like pipe insulation or heater hose and make sure the little blower motor is working.

Peter

Thanks:

You've given me a handful of ideas, all of which I need to educate myself on. They sound like Greek to me right now which is the way of each new job. I'll charge into it today (day off) and see if I can make some progress.

Note that 2 of my 5 daily drivers have the simpler design (TD and converted 240D). I don't look forward to this one.

Don

First check you should make is to follow psfreds advice. Remove the glove box liner and see if the hose is deteriorated (missing) that runs horizontally to the left of the glove box.

Good luck,

Thanks Larry:

Will do

Don

Ok:

1. The hose was shot and had a 'golf ball' size hole in it. Fell apart in my hands:

a. Can I just splice a rubber hose there or does it need to be breathable?

2. By 'little blower' do you mean the blower on the low setting? If not, you lost me?

Thanks

Don

Well, I installed a piece of pipe insulation but it didn't affect the way the unit is malfunctioning....bummer.

I'll have to move on to more sophisticated stuff. I do have another ACC unit out back that I can swap into it, but the way it appears now is that:

1. each time the unit is turned on to full blow it works for about one minute.
2. then it fades until it functions at either 'no blow' or 'low blow'.

I'll take any other ideas.

Thanks

Don

Don,

The answer to '1a' is that the foam line needs to be replaced by foam pipe insulation to keep the air in the line at the temp of the cabin not the hot underdash area.

Not sure about '2'. as I didn't understand that either.

Looks like we posted at about the same time.

The "little blower" is the one to the right-side of the glove box (compartment removed) that the garden size hose is attached to. It is clipped to a holder and can be easily removed. Once in hand, you can observe if the motor/fan is turning. Additionally, with the hose off you can see if it generates reasonable suction (holds a small piece of paper while spinning). When working correctly, the sensor grid (ceiling area where the interior light switch is) should also hold a small piece of tissue. These above were all passed on to me and others from LB and others here on the forum. Good luck and keep us updated.