W124 climate control question - PeachParts Mercedes-Benz Forum

BENZ-LGB · #1 04-20-2007, 03:18 PM

I own a 1991 300CE that I recently purchased. The car has nearly 125k.

Since I bought the car the A/C, front defroster and heater have always worked fine.

Today, however, when I pushed the defroster button I got nothing, zilch, nada. I pushed all the buttons and the same thing, no defroster, no A/C, no fan.

A few minutes later, after driving about half a mile (and the windshield begining to fog up)--air began to flow and everything was working as it should. The climate control is now working fine (at least for the time being).

This is the first time the the coupe has done that and, in fact, it is the first time that any of my Benzes have done that.

Any ideas on what the problem may be?

At first I thought it might have been a bad fuse, but then when everything came back, on that theory was shot down.

Is it a bad climate control unit?

Any suggestions would be appreciated.

BTW, the only thing different about today is that it is raining (a rare occurrence this year in otherwise sunny So. Calif.).

Thanks.

Addbhp · #2 04-20-2007, 04:18 PM

I had the exact same experience two weeks back with my 90 300e. I replaced the 30 Amp fuse, it was cracked but even after fixing that I am still with out the use of the climate controlls. I started a thread not too long ago about this and I've narrowed it down to either the control unit (with a volt meter you can test for this- how is explained in my previous thread) or the resistor that lies under the blower motor. Don't want to replace both as that is expensive. I am hoping to test the relay this weekend and determine next steps. I've actually been too busy and the weather has not cooperated with working on the car. Let me know how you make out as our problems are identical.
Good luck
Mark

Addbhp · #3 04-20-2007, 04:30 PM

If you search "W124 Heater Woes" this is the thread I started.

BENZ-LGB · #4 04-20-2007, 06:05 PM

Thanks.

I looked at your thread. Same symptoms (or I should say symptom, since so far it has done it only once) as mine.

Intermittent problems are a PITA to diagnose.

What I am going to do is wait until it does it again (hopefully that would be never, but you never know) then I will swap the climate control unit with the unit from my 300TE. They are identical.

I'll see what happens then!

In the meantime if anyone has suggestions and/or ideas (or if you discover the source of your problem) please post ehre.

Gracias!

Carson357 · #5 04-20-2007, 06:29 PM

with car and climate control on try turning the key back to the left very slight and see if it then runs, if it does the ignition switch may be faulty

BENZ-LGB · #6 04-20-2007, 07:12 PM

addbhp...check the link below. The symptoms sound like the symptoms exhibited by our cars.

Maybe it will save us both some potentially expensive repairs.

http://mbca.cartama.net/showthread.php?t=4033&highlight=fusable+link

I am going to look at the one in my car as soon as I get a chance.

Addbhp · #7 04-21-2007, 08:26 AM

Thanks- unfortunately I have replaced the fuse, and still no luck. Wil keep you posted.

stevebfl · #8 04-21-2007, 10:19 AM

If it isn't the ignition switch as stated above, I'd suspect the blower motor. The defrost position is the simplest least intuitive position of the system. Fixed duct position, maximum heat, maximum blower, no decisions to make. If it isn't blowing sure sounds like a blower issue.

BENZ-LGB · #9 04-21-2007, 11:23 AM

Quote:

Originally Posted by stevebfl

If it isn't the ignition switch as stated above, I'd suspect the blower motor. The defrost position is the simplest least intuitive position of the system. Fixed duct position, maximum heat, maximum blower, no decisions to make. If it isn't blowing sure sounds like a blower issue.

Steve, but what about the intermittent issue.

Addbhp reports that his climate control works, then stops working, then works...etc.

Mine did not work and then it started right back up after I began to push more button on the climate control unit. It is still working.

I have read elsewhere that the contacts inside the control unit sometime fail and have to be resoldered. Have you heard about this? Is it possible to resolder the contacts or do you just replace the unit?

I've seen rebuilt climate control units going for about $250.00 or so.

stevebfl · #10 04-21-2007, 12:09 PM

So what about intermittant, I can't think of any component in the system that could be intermittant easier than the blower. I also can't think of anything any easier to test.

BENZ-LGB · #11 04-21-2007, 12:59 PM

Quote:

Originally Posted by stevebfl

So what about intermittant, I can't think of any component in the system that could be intermittant easier than the blower. I also can't think of anything any easier to test.

So then, how do you test a blower motor to rule it out as the source for the intermittent operation of the climate control?

stevebfl · #12 04-21-2007, 01:20 PM

The first thing to do is a little observation. Does the compressor quit? Do the doors audibly change position (audible because if the blower is dead for any reason there will be little air coming out unless it's forced air from driving). if driving there will still be forced air is it still cold, does it heat up?

Definitively, look to the x64 three wire connevtor on the firewalll and verify 1-5v signal (varying with blower speed chosen) on the WT/RD wire. Verify 12v on the power source wire BK/GN and ground on the brown wire. If the power stays on and the ground stays on and there is 1-5v on the control wire the system is doing everything it can to turn on the blower. If it is off then one needs to remove the covers and check a little further to tell if the problem is the blower or the blower controller (all down under the wipers in the engine compartment).

BENZ-LGB · #13 04-21-2007, 03:10 PM

Steve:

Thanks, I will check it out.

The one time when my climate control went dead, there was nothing at all happening when I pressed hte various buttons.

Just dead calm.

NO flaps opening or closing, no A/C. In fact, tehre was a trickle of warm air coming through the center vents which increased with vehicle speed. But that was it.

You're right, even if the blower motor was dead, you would still hear the sound of flaps opening and closing since they are operated by vacuum activated from the control unit.

In my case, and I think in Addbhp's case as well, all there was was a big nothing.

Like I said, I will check the blower using your suggestions. If the blower checks out OK then the next time it happens I will swap climate control units with my 300TE.

As always, thank you very.