I don't know. The aux pump won't hurt, but don't expect a big change. The only other thing I can think of is the heater core, have you ever verified that it's not clogged?

Either that or the vacuum pods are not hooked up correctly and are open/closed at the wrong time (seems like a long shot).

Thanks.

I'm assuming by checking the heater core you mean the heat exchanger by flushing it with a hose? I thought the heater core was an electronic module?? I guess I could check that.

What do you know about the temp sensor? Could this be a problem? It looked like a newer (non-original) part when I pulled it.

The vacuum pods appeared to open at the right times when I had everything out. Defrost on defrost. Closed on economy. Etc...

I think I'll buy a pump. They are $80 from ********az.

Hi

I am rather puzzled by this and have no ready solution. However I would suggest a couple of tests before you spend more money on this problem.

1. Is there anyone local to you with the same vehicle with a working CCU? I am wondering if you can swop in a known 100% correct CCU to see if your problems go away......

2. There are instructions in the full MB service manual as I recall on testing the temp sensor for correct operation. That will save you another $30 or whatever for each new part. I was told to replace mine when I had my problems and it turned out the old part was perfectly OK.

Sorry I do not have a more definitive solution for you.

Thanks Toronto,
The temp sensor looks new(er). I don't think I will replace it after looking at it.
I remember seeing the temp sensor check instructions but I'm pretty sure it involves cycling through heating and cooling. Since I have no air, and little heat, I doubt I would be able to tell whether the sensor is working.

I get to take another test drive (commute) in about 4 hours to test my system out since cleaning the temp sensor and checking every thing last night. I will see how the heat works.

Here is where I am at now.
-I want to visually check the center flap pod. Last night I visually checked all others were moving but I couldn't see it definitively so tonight I am going to make sure it is moving. This could not be opening and stopping heat from coming in on other modes? It held vacuum at the switchover valve, but I want to visually verify it works.

Assuming it works, I will go ahead and order a aux water pump and see if that changes anything. That is all I can think of now.

I may also 'flush' out the heat exchanger tonight to make sure it is working properly. But I would assume it works since I get heat in defrost and all heat comes from the same place, right? Come to think of it I don't have a hose to get into the heated garage, so this may have to wait. I don't even know if the outside water is turned on as it is winter. Maybe I will try blowing it out with the air compressor?

My CCU seemed to be working as when I depress the buttons the correct pods (the ones I could see) moved, the monovalve voltage changed correctly, voltage to the water pump was present when it should be, the blower changed speeds on hi and low, I'm sure there was more I checked but that is all I can think of now.

here's what I had a few months ago....cooling working well all summer...got cold out....noticed the car never really could get warm, except in defrost mode. It seemed the heat was working but also was allowing cold outside air thru center vents and defrost vents when in heat mode. Checked all pods ok,,,,changed ccu unit. All now works perfetly. It only take one or two bad connections in that studip box to cause mayhem.

Your symptoms seem to be all over the place in terms of consistency. When you are getting heat from the defrost, is it as hot as it should be, or are you just getting some warm air there but none elsewhere. Same with the floor heat - is it hot or just warm. I just want to be sure that it is not a simple problem in the heating system before you replace the control unit.

Although, your previous symptom of defrost kicking in around 3000 RPM is very strange indeed. What is your engine temperature gauge reading these days? And do you recall what it was reading when your system used to kick on the defrost at 3000 RPMs? - I can't understand why your engine cycling at a certain speed would affect your climate control other than for heat purposes.

__________________
'95 E300D ("Tank") - 231,000 miles
'79 240D ("Biscuit") - 197,250 miles (Sold)
'83 240D ("Ding-Ding") - 217,000 miles (Death by deer)
______________________________________

"Back off, man. I’m a scientist” ~ Peter Venkman

I bought a CCU a few months ago. It did appear to have been rebuilt, but can't say for sure. I will check the pins voltage tonight when cycling through the system to see if it works.

I would be against buying another CCU until I am 100% positive the CCU is a problem. But as I know from my own stuborness, it usually seems that the problem I am sure it is not, turns out to be the problem.

I will check the pins voltage tonight.

It is hard to say how hot it is. I really have nothing to compare it to. All I know is this past summer with no air, and the heat kicking in made the heat coming out of the defrost this summer seem scorching!! Now, in the cold winter it seems warm, but usually after about 20-30 minutes of driving I have to turn it off because the car gets hot with my jacket on. But should it really take that long?

In my opinion, the air is just warm. What could this be a sign of if this is the case?

My engine temp gets up to 80-85C. I don't ever recall it being to different from that. Perhaps up to 90C in the summer but I just assumed that was because it was warmer out?

In my opinion the kicking in of the heat was due to a faulty aux water pump. When I measuered the current on it (hooking the ground side up to the connector and then bridging the positive side) it was immediately around 16 and I was told it should be around 1 amp, I didn't check any more as I didn't want to fry anything and left it unplugged and now I have completely taken it out.

I replaced the monovalve and unplugged the aux water pump at the same time. The heat seemed not as hot immediately after doing this around September. Here is another theory. The heat exchanger is partially block so flow is diminished. The aux pump would pull hard to get the coolant to flow through and was overworked. Then when I took it out I can't get the same flow through??

One solution, if you can live without it for a while, is to send the CCU to GDL for testing. I believe they will test it for free, give them a call.

does anyone know how to test these things?? out of the car?? Is there a pinnout somewhere?? I might be inclined to build a tester.

Who is GDL?

GDL:

http://www.gdl-online.com/main.html

They rebuild CCU units, cruise controls, etc. I have bough a CCU and cruise control (amp and actuator) from them. They are very helpful.

Well, the problem seems to be fixed. I am now getting heat out of other modes.

I'm not quite sure what fixed it but here are my thoughts.

1-The temp sensor was blocked by that huge moth and the system was not able to respond for heat other than full heating on defrost.

2-I plugged the monovalve back in. I know it defaults to open so it should be hot then no matter what, but perhaps when it was trying to tell the monovalve to open in something other than full heat (defrost) it left the circuit open?? It is a stretch on this one, but this and the moth are the only two definitive things that have changed.

I don't plan on ordering the aux water pump anymore. I will leave it as is with just the elbow there instead.

Now that everything seems to be functioning properly I will start trouble shooting the a/c sometime in the future!

Thanks for everyone's help and input.

The monovalve only has two positions: open and closed. In normal operation, there is no in-between. When the electrical circuit is open, the valve is open. And vice versa.

I didn't necessarily mean the monovalve circuit. I meant the monovalve circuit being left open was affecting the other modes when it was sending the signal to the monovalve. But the reason I put a couple question marks is because it didn't make any sense why it would work, but then neither did removing a moth!

On my 300D, disconnecting the monovalve causes the heat to be unbearable, no matter how cold the weather is.