w124uk

Tried the search but didn't come across anything that would help me!

The car is a 1993 280E with factory fit r134a aircon.

The A/C works fine if the temperature is moved to the coldest position in the selector on the dash, if I move it to adjust the temperature to have somewhere in-between, it just gets hot.

Has anyone had the same problem? What's the fix for that? I can either sweat or shiver in the car, all I need is a 'pleasant' temperature... Hope it's not too much to ask for ;-)

Thanks in advance!

ps2cho

A lot of the time the a/c unit fails on the inside and can cause what you are experiencing. If you wanna pull the unit out and try resoldering any cracked joints, it may resolve your problem.

w124uk

Hmmm, what do you mean by 'A/C unit'? The air mixer or the control panel?

Marian

Hi.

Either the sensor in the interior light assy does not work or the control panel is shot - which is the usual fault. This is a comon problem and should be an easy fix with a used part from the breakers yard. Watch out for different control panels - thery're color coded an haved been changed at least twice over the years.
You may also check out the German Forum - but of course all info is in German
http://archiv.mb124.de/archiv/Heizun...nd_Fehlersuche

BR,
Marian

w124uk

Thanks!
I'm just reading that German post, it's a great find!
I'll look into that pretty soon. I didn't know the heater control worked that way on the w124!

ds190

Related to that is the ventilation blower that draws air across that sensor. More often than a bad sensor, that blower motor stops working and the sensor sends either too cold or too hot signals to the ACC unit.

I've had an issue with two of these blowers out of five 124 cars.

Real1shepherd

If we're talking about the same thing, that sensor sits in a plastic bracket on top of the casing that seals over the blower motor? I don't really have the same OP problem, but it seems that I have to turn the dash temp way high towards warm (like 75 degrees), to get the fan to moderate and not blast out cold air full strength using the 'Auto' button. This is on a day over 92 degrees....but I think the cab has sufficiently cooled down at that point. Last yr I ran the A/C very infrequently, so I don't have a recent point of reference. I'm not sure there is anything wrong....yet.

Definitely the blower motors are problematic. Usually the brushes are worn past 1/4", but in mine it was the bearings themselves. I freed up the bearings, but now I smell the bearing oil that I used. Hopefully that will disappear over time. Those squirrel cages are dainty little things....the end of the shafts were rusted and the prospect of pulling those off intact looked dubious, to say the least.

Kevin

tazz5150

Actually I'm having similar problem.

I'll keep checking on this post to see how the problem gets resolved. If you can, please guide us in how you fixed this problem, for an idiot to be able to follow

thanks!

ds190

Interesting info, but no we are not talking about the same thing.

Marion said "sensor in the interior light assy", and I said "ventilation blower", also known as temperature sensor interior air and aspirator blower. The sensor in the interior light assembly is connected to the ventilation blower with a foam tube that runs across the top of the windshield and down the right side into the dashboard. The ventilation blower is wrapped in foam and attached inside of the dash under the right side air vent. This blower runs anytime the ignition is on, not matter what button is pushed in on the ACC unit. If it stops running, the interior temp sensor does not sample the cabin air accurately, and if the A/C refrigerant is charged correctly, typically the ACC with the "auto" button pushed in will blast full fan cold air or turn down to almost nothing. If you push the high speed or low speed fan buttons, typically there is no change until minutes later if at all.

To check if the vent blower is working, turn on the ignition and/or start the car, and hold a piece of paper 1 x1 cm (.5 x.5") up onto the grill in the interior light fixture. It should stay up there, no matter what the setting on the ACC unit. If the paper falls right off, the ventilation (or aspirator) blower is not spinning.

On two 124 cars, I have removed that blower from under the dash, cleaned off all the dust, unsnapped the top over it's fan blades, lubed with silicon spray, and bent the tiny wire brushes just a bit to insure good contact. Both AC systems worked as normal after that

If the AC system is correctly charged and the blower motor works, checking the operation of the ventilation blower is the next thing the ACC Service Manual lists to check.

Hope this helps.

Edit- for our British Empire friends, the ventilation or aspirator blower is in the LEFT side of the dash!