c280 1997 Climate Control - classic cold + hot blow - PeachParts Mercedes-Benz Forum

BrazBenz · #1 07-03-2007, 08:45 PM

I am dealing with this problem in my car. Did a LOT of searches, learned a lot, spent some $$$ and still no positive outcome.
I will make a few questions that may help me to advance.
Problem: Intermitent (almost rare) hot + cold air blown by the climate control system. (hot in the side vents and cold in the center ones) User command: COLD (so the heat is undesirable)
More frequent in traffic jams. (can't understand why)
Usually setting the termostat to a MUCH lower temp fixes the problem.

Actions so far:
At first I simply blocked the heater hose. (don't need heat im my city). Result: No more heat (of course) but the thermostat would NEVER turn the compressor off... car became a freezer.
then...
I decided to replace the duovalve as a relatively low cost alternative. Everything was pointing towards an intermitent duovalve. Result: NONE!

So, I am back to diagnostics...

Questions:

1 By design our climate control systems truly mixes hot + cold air under specific circunstances ? Which ? In other words: is it conceivable to have the compressor providing cold and the heater providing heat SIMULTANEOUSLY ?
2 Why the thermostat (sensor?) would ignore a frozen interior and not disengage the compressor?
3 If the answer to 1 is positive, which are the sensors that command cold production and which the ones that trigger heat production? Could changing them be a cheap solution or is this more sophisticaded? (made thru an integrated circuit, for instance)
4. A bit redundant: Is the control unit "intelligent" or just a switching box ?
5. Any possibility that a failing auxiliary water pump may be part of this mess?

After throwing out the 120.00 for the duovalve I am trying to be more sure with new expenses.
TIA !
Jorge

Richard Wooldridge · #2 07-03-2007, 11:33 PM

I suspect that your auxiliary water pump is not working. The mono/duo valves need to have the pressure that the auxiliary water pump produces to make the valves work properly. when the car is idling at a stop light, there's not much pressure from the engine water pump, so the valves cannot stay closed. When the car runs at a higher engine rpm, the valves start closing again. The solution is to replace the auxiliary water pump, or change to a different type of valve. I drew up a drawing of the change I made on my '82 380SL, which had the same problem. It's on one of the diesel threads, if you have trouble finding it I can probably look it up.

TMAllison · #3 07-04-2007, 12:12 AM

Did you start by pulling up this data from your CCU?http://www.continentalimports.com/ser_ic40142.html

BrazBenz · #4 07-04-2007, 02:56 PM

Quote:

Originally Posted by TMAllison

Did you start by pulling up this data from your CCU?http://www.continentalimports.com/ser_ic40142.html

Terry,
This is GREAT! BTW, all S. Brotherton site is great.
Many thanks.
The car is being serviced and as soon as I get it back I will run the diagnostics. Answering your question: No, I thought that the Star Diagnostics would be required.
Best Regards, Jorge

BrazBenz · #5 07-04-2007, 03:13 PM

Quote:

Originally Posted by Richard Wooldridge

I suspect that your auxiliary water pump is not working. The mono/duo valves need to have the pressure that the auxiliary water pump produces to make the valves work properly. when the car is idling at a stop light, there's not much pressure from the engine water pump, so the valves cannot stay closed. When the car runs at a higher engine rpm, the valves start closing again. The solution is to replace the auxiliary water pump, or change to a different type of valve. I drew up a drawing of the change I made on my '82 380SL, which had the same problem. It's on one of the diesel threads, if you have trouble finding it I can probably look it up.

Richard,
I will check your change later today.
I already called the workshop (the car is there) asking them to test fuse/aux water pump.
This site is all about synergy: take a look to at the text below, pasted from another article by S. Brotherton, from the site referred by Terry.
While it says you may be true it also warns that the control module may be dying...
Thanks for your support, Jorge

"HEATER WATER VALVE
The last factor involved in Mercedes-Benz climate control is the heater water valve. From simple vacuum-controlled, on/off water valves to multiple pulse width-controlled water valves, each model can be different. Early models used auxiliary water pumps to help when temperatures got too cold. Systems starting with the 124 chassis have used the auxiliary water pump to maintain a uniform heater core temperature. Failure of this pump causes a couple of nasty problems. The first one is straightforward, if you catch it before it damages more than one pushbutton controller. The pump locks and the current flow burns out the controller — a good thing to check out if you are replacing the controller.

The second problem caused by the pump (or lack of pump) is more subtle. It shows itself as sporadic, sudden bursts of hot air, which are produced when a car that is mixing heat and cold to achieve control sits at a light. Due to a no pump and poor engine flow condition attributed to the slow speed, the water valve is opened to full to try and raise the heater core temp. When the car starts moving, the water flow grows rapidly and the heater core goes full hot before the valve can control it.

BrazBenz · #6 07-06-2007, 02:33 PM

Quote:

Originally Posted by Richard Wooldridge

I suspect that your auxiliary water pump is not working. The mono/duo valves need to have the pressure that the auxiliary water pump produces to make the valves work properly. when the car is idling at a stop light, there's not much pressure from the engine water pump, so the valves cannot stay closed. When the car runs at a higher engine rpm, the valves start closing again. The solution is to replace the auxiliary water pump, or change to a different type of valve. I drew up a drawing of the change I made on my '82 380SL, which had the same problem. It's on one of the diesel threads, if you have trouble finding it I can probably look it up.

Richard,
I still not tested my aux water pump.
Going deeper on this to improve my understanding:
- Should the pump be ALWAYS turning ? (is this the price for keeping the valve shut?)
- Please look my question 2. By blocking the fluid should'nt everything be OK? So, how to explain the temperature just goes down and down?
Thanks in advance for your insights.
I reviewed your implementation. May well follow your steps. But need to be sure the CCM is ok before.
Jorge

Richard Wooldridge · #7 07-06-2007, 09:51 PM

In all positions of the climate control except economy and off, the AC compressor is running. Heat control is maintained by adding heat to the cold air. If the heater control valve is shut, or the hose is pinched off, as you did, the air can only get colder and colder, as the ac compressor is still running. As to the question of whether the auxiliary pump should always be running, My brother has the factory manual at his vacation home right now, so I cannot give you a definitive answer, but I do suspect it will be running in all positions except economy and off.

BrazBenz · #8 07-07-2007, 11:35 AM

Richard,
Many thanks for your clarification. I am finally starting to understand the complexity of the MB climate system.
It becomes clear why troubleshooting it is so difficult.
Living in Brazil (where parts are EXTREMELY expensive) I have to move very carefully.
Now I will do some experimentation on my own and with the guy of the service workshop trying to isolate one basic point: is the CCM malfunctioning or not ?
If it is Ok then I will probaly go your way in finding a circumvention to the heater control valve "odd temper".
As a last resource I can order the parts from the US (do that regularly either by internet or when I am there) (I have a son living in Florida).
So my nest two steps will be:
1. Test the aux water pump.
2. See if the diagnostics mode provides me some new info
Thanks again and best regards.
Jorge
PS: This is a VERY hot/warm climate. I can live without the heat functions (except for a few trips to the mountains if it is in the worst of the winter) but NEVER without the AC. I wonder if just removing the aux pump and freeing the flow resistance could not accomplish what I need.

david s poole · #9 07-07-2007, 12:31 PM

richard,correct me if i'm wrong but does'nt the aux water pump exist to aid the heating in cold climates and as such only runs below a certain temp[30degF]?

Richard Wooldridge · #10 07-07-2007, 06:02 PM

Hi David,
As I mentioned in my previous post, my hardcopy of the factory manual isn't here right now, and you could be right, but if you are, the monovalve design isn't up to it's task. I made the assumption that the monovalve requires the auxiliary water pump's pressure in order to fully close because of the several failures I've seen. I know the aux pump runs all the time on my '82 300, and the monovalve works ok. But, it could be the result of a failed temp sensor... I"ll have to go through the operation again in the manual to satisfy myself. So, I'm sorry if I've misled anyone, but the monovalve is very troublesome, and in my opinion, the best thing to do is replace it with a vacuum operated valve that operates positively. Since changing the valve for a vacuum one in my '82 380SL, I've never had such terrific AC! The other day it was into the 90's here (a very rare occurence), and the AC would get as cold as I could stand, had to run the dial up into the white to be comfortable. Another benefit is that the car starts off after standing in a hot parking lot and provides cold air as soon as the fan begins blowing, ie, the heater core is shut off when the car is off.

Regards,

BrazBenz · #11 07-08-2007, 10:06 AM

Well, I moved one step more:
Tested the aux water pump and the duovalve.
Environment: Engine at idle speed with the hot + cold blowing HAPPENING.
First place a screwdriver on the two bodies of the duovalve. Clearly they click and provide mechanical feedback at every 5 seconds. So, the CCM is commanding right and, in principle, the valve is reacting well. (this is good. I was afraid that the CCM could not be issuing the right command)
Besides, the feeding hose for the aux pump pulsates when the valve closes.

After that tested the aux pump: turned the car off, pushed the REST button (that forces the pump to work) and it was working. (very easy to confirm with the screwdriver) (the device itself works very smoothly)
Then turned the engine on and, again, the pump seems to work. (it is not that easy to feel it on the screwdriver)

So, preliminarly I have a contradiction: the hot air is blowing, the aux pump is turning and the valve is closing...
Of course my testing is partial, as:

1. The motor of the pump turns. Something may be wrong in the pumping sector itself. Stuck and then broke, for instance?
2. Something may be bad on the duovalve, altough it is brand new

Next steps:

- Confirm that the two devices are performing right
- Diagnostics mode

I wonder if some flap should be closed and is opened.
Well, te positive side is that the CCM seems to be Ok.
The negative is that, intermitently, the hot+cold blow still happens.

One new finding: When the external temperature and the wanted temperature are closer the failure becomes easier to replicate. This leads me to suspect of the temp sensor. But then why would the CCM be issuing "close" pulses to the duovalve?

Thanks for all your cooperation !
Jorge

BrazBenz · #12 07-13-2007, 12:43 PM

Run all the diagnostics (from the climate control unit)
1. CCU seems to be Ok and sensors are issuing correct data
2. Big discovery: Version Coding was not Ok. I recoded it (based on my understanding of the instructions) and the system is performing almost OK.
3. I found an intermittent diag code pointing for the AUXILIARY WATER PUMP!!!!!.
So, probably Richard was right all the time. (and I had two issues instead of one) . This is true IF I did the right Version Coding.

So I am back asking for support - now on version coding.

Let me show what I did (based on Alldata and StartekInfo)

Car is a 1997 C280 L6 w/ push button CCU (buttonsd around LCD window)

Values _________ to be used if
COD - new unit - no programming so far
00 - Serial interface (K1)
02 - K1+K2 (as of MY 1997)
08 - refrigerant fill level check switched off (up to MY 1997)
10 - serial interface K1 + K2, refr. fill level switched off (as of MY 1997)
18 - with engine/climate control electric cooling fan
32 - aux cooling fan not available (as of MY 1997)

I decided for 10

Reasons:
a. Newer models seem to be K1+K2
b. It is said that 1997s have fill level check off
c. 10 is the combination of a and b
d. There is NO engine/climate control electric cooling fan (the car has the radiator propeller+ clutch) and the two auxiliary electric fans)

So, from all I said I am not totally sure about the K1 and K2 thing. All my searches did not suceed...
Any help is VERY welcome.
Jorge

PS1- Thanks for all the help I received do far
PS2: My CCU is A 202 830 1485 (as per EPC)
PS3: same source: instrument cluster is A 202 540 6697

david s poole · #13 07-13-2007, 02:26 PM

after reading your posts i recall having a 97 car brought to me where the climate control was doing silly things.discovered that controller had been replaced and not version coded[1 unit works for several cars depending on version coding] i coded controller and bingo no more problems.

BrazBenz · #14 07-13-2007, 05:43 PM

David,
I know for sure that this car had it's AC system serviced. The code that was in the CCU was 1, which SEEMS to be inadequate.
So, in my case, they probably recoded based on wrong info (this is not a single task, given the diversity of options)
So, I am waiting for the final definition for the right version coding. But the change I made brought very good results as compared to the previous situation.
Jorge