1987 300TDT (W124) Climate Control Problems - PeachParts Mercedes-Benz Forum

swogee · #1 10-27-2005, 12:57 AM

The climate control system in my 1987 300TDT seems to be operating improperly since I cannot get heated air out of the footwell flaps.

I have searched for posts on climate control problems like mine, but I haven't found one yet with symptoms like mine.

When the system goes into heat mode (temp dial between 22 and 18, EC button pressed, fan on auto, outside air at 55 degrees F)), the air seems to only come out of the defrost vents and the lateral vents on the ends of the dash. The climate control (ACC) seems to switch between full heat out the defroster and lateral vents and cool air from the center and lateral vents to try and keep the interior temp at the right temp. The ACC doesn't seem want to use a medium fan setting with only warm air for some reason.

Placing the temperature dial at max with the solid down arrow and outline up arrow button pressed (with or without EC marking), and the fan button at auto seems to make no difference, the air still comes out of the defrost and lateral vents.

Additional info:

The fan operates properly at min, max, and auto when pressing each of the buttons.

Occasionally when I turn the climate control on, I can hear a faint clicking sound from behind the glove box area and nothing happens initially until after 5 or 10 seconds. There are also occasions when I press the off button, and the climate control system runs for about 15 seconds, and then it shuts off.

The only time I am able to get air out of the footwell vents is when I press the button with the solid up and down arrows.

I have tested all of the vacuum pods and they all hold 15 in Hg of vaccum except the center vent pod. I have also swapped the hoses for center vent pod and the air diverter flap pod to get air around the bad center vent pod temporarily.

The air sample fan is working properly since it seems to hold a small square of paper at it's intake point on the dome light.

I have the MBZ Climate Control Service Manual, and I have run the functional tests and based on the results the manual says to run the electrical component test which seems to require a special test instrument/breakout box.

Does anyone have any ideas on what component might be bad?

At this point it looks like it might be the control unit, but I need to run more tests. Any thoughts and ideas are welcome.

Thanks in advance.

-Steve

jcyuhn · #2 10-27-2005, 10:23 AM

Try unplugging the auxilliary electric water pump under the hood. If it's shorted out, the climate control will go a little (OK, a lot...) berzerk whenever it switches to heating mode. You're seeing the protection mode, in which the control unit is protecting itself from the shorted aux. water pump.

The pump sits underneath the windshield washer tank. There's an electrical connector right there, just unplug it.

How does the system operate when the interior of the car requires cooling? Does it behave in an acceptable manner?

- JimY

swogee · #3 10-27-2005, 10:58 AM

My A/C system has no R-12 in it so the compressor will not turn on, but other than that the fan comes on and air comes out of the center and lateral vents as it should when the two buttons with solid down arrows and outline up arrows are pressed. No air comes out of the footwell vents while in the cooling mode, which is proper operation I believe.

I'm not sure what effect the swapping of the diverter flap pod line and the center vent pod flap lines will have on heating and cooling, but the footwell flaps should still open as necessary.

When is the diverter flap pod used anyhow?

-Steve

swogee · #4 11-07-2005, 11:51 AM

I'm think about replacing the control unit with a Programa rebuilt control unit. Has anyone heard good or bad things about the ACC control units rebuilt by Programa?

-Steve

jcyuhn · #5 11-07-2005, 12:50 PM

The diverter flap opens when the interior temperature of the car is far above the setpoint. It's something of a maximum cooling setting. The diverted air passes through the a/c evaporator, but bypasses the heater core. The 'normal' cooled air passes through both the evap and heater core.

The real effect of swapping the diverter and center air flap is quite small. If the control unit calls for heated air out the center vents - which it almost never does - the center vent air won't be heated.

Don't spend to replace the control unit until you disconnect and/or check the aux heater pump. If it is shorted out - which they all do, eventually - you'll get the same operation out of the rebuilt unit. If the aux water pump is shorted, the control unit goes into a sort of protection mode in which it is non-responsive. This occurs only when the control unit switches on the aux water pump - anytime it is calling for heat. In straight cooling mode it will operate correctly. Your symptoms seem to match these characteristics.

- JimY

goat · #6 11-07-2005, 11:27 PM

I have an '85 300D - W123. I only get air out of the dash vents and defroster, like the original poster. Also, the air is only barely warm most of the time, even if the dial is set to "MAX."

I can shut off the engine, let it sit for 5 seconds or so, and restart it, and I will get hot air for 15-30 seconds or so. Then, as I drive, it will gradually cool off until it is barely warm.

Is the W123 setup similar? Is this a failing aux. water pump?

swogee · #7 12-20-2005, 11:37 AM

After using the climate control with the new aux. pump, it seems as though the system still has one issue. The climate control seems to work 90% of the time, but on occassion there is a clicking noise that seems to come from behind the center console or near the glove box. One time the clicking noise persisted for a while, and the climate control shut down completely. I can stop the clicking if I shut the ACC off. When the clicking noise prevents the ACC from functioning, the ignition needs to be turned off for a bit to reset the climate control. Sometimes the ACC will click for a few seconds, and then the system will turn on.

Does anyone know about this strange behavior?

Thanks in advance.

-Steve

#8 12-20-2005, 12:27 PM

I have the same ignition switch issue with my 300D, apparently the ignition needs to be replaced. Does anyone know if the tumbler portion, the switch portion, or both parts need to be replaced?

speedy300Dturbo · #9 12-20-2005, 05:39 PM

I recently experienced the annoying clicking symptom with my 1987 300D, along with max heat when the car is at speed. Replacing the aux water pump helped for a little while but it did not completely eliminate the problem. Replacing the pushbutton unit did the trick.

swogee · #10 12-20-2005, 06:22 PM

I was wondering if the control unit was the cause of the ACC clicking noise or not. It looks like I might have to spend the bucks on a new control unit after all. I thought the new aux pump might solve all of the problems, but it only cured the max heat at speed and the heat coming only out of the defroster vents problem. The ACC seems a little less erratic with the new aux. pump but not quite normal.

Craig, do you know how the ignition switch can cause the clicking with the climate control? I'm not sure if your symptom would have the same cause as mine since you have a W123. The ignition switch on my 1987 300TDT has been replaced at some point in the past.

speedy300Dturbo, where did you get your climate control unit from? I know they are available from Beckman and Programma (from World PAC) as rebuilt units. Do you know which one is better? Have you heard good or bad things about either? I seem to recall reading that the Programma units are hit or miss.

Thanks for responses.

-Steve

speedy300Dturbo · #11 12-20-2005, 07:01 PM

Steve,

I think I went through pretty much the same ordeal that you're experiencing now. The new aux pump helped but did not restore ACC operation to normal. The clicking noise (coupled with intermittent blower operation) seems to be caused by bad signals from the pushbutton unit to the associated relays. I managed to get a good used climate control unit from another 87 300D.

Another thing to note - according to MB the 1987 300D/TD pushbutton unit is specific to those models - and not interchangeable with other years. As far as the Programma units being any good or not, I'm really not sure. They do have a three year warranty though.

nuckingfuts · #12 12-20-2005, 09:53 PM

I have been having the same clicking. It took me 45mins of idle before I got the heat to work. Just installed a aux water pump today and the prob went away. I am curious though, if what you all say is true and the unit is bad will a climate control system out of a 300TE work?

saf · #13 03-15-2006, 10:48 AM

I have anoying sound seems to be coming from under the dash possibly the climate control or the area around it.. It sounds like WaaaAAAAAA WaaaAAAAA etc. I thought it was the blower but I listened carefully and it was not the blower.
It only stops if I turn the acc unit off by pushing the button at the far right
marked with (O) . Any idea or help