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mbtjc 09-20-2004 01:40 PM

w126 erratic A/C
My A/C is quite erratic. First, when I start the car, it takes a good 10-15 minutes of driving to start blowing hard and to get cold. Then when it gets may blow cold and hard for 5 minutes, then soft and warm for a few. So fan speed and temp have a mind if their own. When it does blow cold and hard, it's ice cold. There's also a "cold" and "colder"....cold is decently cold, but them sometimes it's ice cold. So...obviously, I'd like it to blow ice cold all the time and preferably right off the bat or very soon after. I moved to FL, so this is even more critical now! :cool:

LarryBible 09-20-2004 03:05 PM

The first thing that I would check is the sample blower motor and associated plumbing. There is a little fan that draws air over the cabin temp sensor.

I am not intimately familiar with the 126 chassis, so I can't tell you where to look for the fan and plumbing. If you have a service CD, you can learn where it is from that. If not, maybe one of the 126 guys will chime in. If that doesn't happen, post this in the diesel discussion forum. There are many 126 guru's who hang out there.

Good luck,

mbtjc 09-20-2004 10:01 PM

I take it this little fan is up there somewhere in the area of the dome light? I guess I will pop that out and see what I find. Thanks for your help, and I might try the diesel forum.

psfred 09-21-2004 01:24 AM

The temp sensor is up in the dome lamp assembly, but the sampler blower is actually located beneath the right side outer dash vent. You need to remove the glove box to get to it.

You can test it by holding a small (1 cm square or so) bit of paper up to the little grill. If it won't stay up, the blower is either off the hard plastic and rubber hose or the motor is bad.

To remove the glove box, open it, remove contents (mine is usually completely full!) and take the two screws out that hold the latch ring in. Remove the push rivets by prying up the center section and then the base (may be stuck pretty bad -- the plastic distorts with time. If so, get new ones). There are 8 in the 124 chassis, probably 8 or so in the W126.

Once the box is free, pull the lamp assembly down and push it back up through the mounting hole, then pull the top center of the box down to clear the molded hook there. The box will then pull out.

Sampler motor is clipped to the dash lower panel right under the vent.

When re-installing, put the hose on the motor before you put it back in the clip. Otherwise, the hose tends to come off if there is any tension on it.

If the sampler motor is working properly, you need to pull the pushbutton unit and spray contact cleaner on the temp wheel rheostat.


gregga 09-21-2004 12:12 PM

The W126 has an airbag instead of a glove box. You need to remove the panel under the dash on the passenger side and stand on your head to see the blower . It's between the end of the heater box and the right kick panel. The foam adapter to the tube has a tendency to deteriorate.

psfred 09-21-2004 07:51 PM

Presence of passenger airbag depends on model year. Up to 87 (the 300SDL), there is a glove box, no passenger side airbag. The 81-85 models don't always have a driver side airbag either, I believe.

On the W124, the hose is solid rubber, not foam, but I've not dived into the W126 yet (probably this weekend).


MarkPavelka 09-21-2004 08:49 PM

Just a comment...I have a 420 SEL and had a very similar problem...after several trips to the MB service depts - I finally took the climate control out and found the potentiometer had all tree solder joints loose. I soldered these and now works like new. I had hot/cold blasts; erratic fan speeds; very irregular temperatures.

Not sure this helps but the disgnosis was correctly provided on this website by some of the kind people posting directions and help!!!

Good luck!!

mbtjc 09-22-2004 02:02 PM

Thanks for the responses. I will try the fan first, since it is easier. Mark, so you removed the switch panel unit and took it apart and resoldered the joints? Can you be a little more specific with what you did and maybe give a few pointers if any? Thanks again!

darius 09-25-2004 03:44 PM


I am currently attempting the identical repair on my W126. I have the blower motor, which I bought from a reputable source (so I believe it to be correct). P/N 000 830 19 08. I removed the glove box and cant see where this little motor goes. Do I have to remove the lower kickpanel? No messages on this subject have mentioned the kickpanel removal.

My W126 is a 1987 420SEL. No airbag.



psfred 09-25-2004 06:42 PM


It should be clipped to the lower panel directly under the side vent by the door. Probably impossible to see it without a mirror, but you can reach around left-handed. One two wire plug, body of motor fits into a metal clip attached to the kick panel.


mbtjc 09-27-2004 12:40 PM

I took out my glovebox, and the little motor sits right there on the right, ya really can't miss it. It's got a electric plug-in and a rubber line which goes to the temp sensor.

Here are my findings: The visible portion of the rubber hose is intact. The little fan blade on the motor is spinning. However, when I take the rubber hose off, I don't feel any suction at the motor inlet. I also don't feel any suction at the temp sensor end of the hose....but again, the motor visually works. Finding #2: When I take the hose off the temp sensor and blow hot air into it with my mouth, makes no difference in what the A/C does. Setting is on auto and on cold.
Finding #3, when I take the A/C off auto and put the blower speed on high, it works like a charm after it gets cold...almost to the point where it's too cold and have to put on low blower speed.

Any ideas?

darius 09-27-2004 12:57 PM

As bizarre as it is, my whole motor assembly is not located there to the right of the glovebox. There is no rubber hose and no wiring.

I wonder if mine was relegated to the lower kickpanel to where it was moved in '88 when the glovebox went away in favor of the airbag.

Anyone have a '87 420SEL and can confirm that the sampler blower motor/aspirator is there?

Re: MBTJC: I heard from others that the motor will continue to run, but if the suction isnt strong enough at the end, it wont matter. Strangely...I have a car with the glovebox removed and no sensor and you have a bad sensor. Sorry that I cant just send my replacement your way. Of course, if I find out that I've got no unit to replace, I may have a brand new unit for sale.



mbtjc 09-27-2004 01:55 PM

I have a bad sensor or a bad sampler motor? It seems I can't get anything from either since I don't feel any suction AND the A/C doesn't behave differently when I blow into the temp sensor. I find it unlikely that both are shot at the same time.....but who knows...

gregga 09-27-2004 04:01 PM

I did a search on "sampler" and found this one that has some attached pictures. Maybe they'll help.

psfred 09-27-2004 11:39 PM

It takes a bit for the thermistor to repsond to temp changes, and again a bit for the climate control to switch modes or temps. If it's been delivereing heat, the heater core will have to cool off before the delievered air cools down.

If you have no suction, the sampler motor is bad, probably either full of lint from the insulation, or not spinning fast enough. You could have a broken hose, too, but that should be obvious, they don't usually break anywhere but at the pump.

I'd get a new sampler blower if it doesn't generate any suction.


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