A/C control help
 

Anyone had problems with the A/C controls on the ML? I have a 98, and my A/C control doesnt seem to want to turn on the compressor. If i fiddle with it long enough, turning it from the blue to red....after several minutes of playing with it...the compressor will kick on, and begin functioning correctly. The freon level is good, no leaks, and the compressor works flawlessly, once it is activated...Can anyone please help? Thanks

defective switch?
 

test the switch. . could be the switch sometimes...

Thanks for the reply
 

Thanks for the reply....Could you tell me which switch to test...and if possible where it is...and how to test too....Thanks.

I've never removed that panel before...
 

ask gilly! he should know.. btw: I'm in the process of replacing the dial switches for the heat/ on off etc.. soon too =( for a friend.. I hope its easy to change hehe

Never had a problem like this. Probably what is being referred to is the AC on/off switch, next to the fan speed switch (the one that enables the AC compressor to work. Never needed to test it though. Since it eventually works, possibly what needs to be done is the AC switch engaged and then just WAIT to see if it starts to work. In some cases there may be a short waiting time before the compressor will actually engage.

Gilly

A/C switch
 

Gilly,

Thanks for your advice...The A/C works great(when the compressor engages), and it works like it should most of the time...but every once in awhile, when you turn the engine on, the compressor just wont want to come on...I thought it might be a short somewhere, and I played with the dials the last time it happened...and pressend on the A/C and recirculate buttons, but it never came on....When I got to my wife's work, I was going to try pulling the fuses out and reinserting thinking it might reset....but the A/C compressor kicked on all by itself. Since this time, I havent messed with any of the switches(A/C, recirc, or any of the three dials), and it has been operating normally. Im scared to touch the dials thinking it might make the compressor stop again.

Someone else suggested it could be the evaporator temperature sensor...what do you think? Its a 30 dollar part, and Im tempted to try...

The freon if fine, and like I said when the A/C works, it blows out ice cubes...

Oh, if you think it could be the Evaporator temp sensor, can you tell me where I can find it? and if theres a way to test it?

Thanks for your help.

anyone know...
 

if the 3 heater control dials in the ML are switches or uses cable system??

The fan switch is an electrical switch, the temp dial is a resistor, and the knob to switch modes is cable.
On the AC not working, I would say that there is only a problem if in fact the ac compressor really "needs" to run to obtain the correct output. So, if it kind of a cool morning, lets say 50 degrees, and you are calling for cabin temp in the "white" zone (70 degrees or so) then it may be appropriate for the ac compressor to not engage. If on the other hand it is a hot day (80 degrees lets say) and the inside temp dial is set all the way to the minimum temp, then I'd expect the ac compressor to come on fairly quickly.

Gilly

Ok, I think I know which dial it is..
 

Gilly,

I think Ive narrowed it down...unless its just some fluke that the A/C comes back on after we mess with this dial.

By the way...it isnt temperature related, because the other day, it was 90 degrees outside, and 118 inside the ML, and the AC compressor refused to come on.

The other day, my wife called and said that the AC was out again, I told her to turn the middle dial(red, white and blue) dial all the way to the red and leave it there for a few seconds(I know it sounds like I was trying to torture her), and then slowly turn it back to the blue....Voila! The AC compressor kicked on...

What do I need to check or change out? I have noticed from my own fumblings with the middle dial, that it turns very easily...it doesnt have as much resistance as it used to...maybe the contacts are worn out...or its losing contact somehow...anything that can be done would be a tremendous help...

It could be the resistor switch gilly mentioned..
 

unfortunately from the pic.. it looks like the 3 switches is one unit.. so you will need to replace all 3 switches =( its called the "operating unit" let us know how it goes! Gilly is it possible if you gave us instructions on how to remove to access this "operating unit" switch unit?

replacing bulb in a/c dial
 

Tabo, Gilly or anyone else, how would I gain access to the bulb, part 12, in the picture you posted? Thanks.

a/c
 

Strange sounds like my current problem. Went to get haircut,92 outside, a/c worked fine when I came out the a/c would not cool. Checked the fuses and the small 30 amp fuse was blown and I replaced it but the compressor would not engage.

Took to local garage and they checked the freon and said it was ok (static)
and said the controller had the compressor locked out and I would have to take it to Mercedes dealer since they have computer.

Drove 2 hours to dealer and left the vehicle. They just called and said the compressor is shot. and it will be about $1500.00 to repair. The clutch would not engage but when I checked it , it turned freely. They used a term I have never heard before . The compressor has equalized. I am wondering how the compressor could go bad with no noise and no loss of cooling capacity.

I asked them if they got the compressor to engage and the service manager said he didn't know. He was going to have the shop foreman check and get back to me.

Gilley, do I need a second opinion?

just in
 

Dealer called back and said the clutch is all that is wrong with the a/c.
Pressure was equalized because the clutch would not engage but the clutch is only 25 dollars less than the entire compressor. Can this be correct?

I am out 125 for diagonastic charge . Can you do a twelve volt jumper on clutch to see if it will engage? Or is there another way to test.

Any ideas?