Accessing, Replacing Evaporator Temperature Sensor 92 300D 86 300SDL - PeachParts Mercedes-Benz Forum

shertex · #1 07-02-2012, 08:59 AM

Could it be that I'm the only one on this forum with not one but TWO bad evaporator temperature sensors?

According to PO, my 86 300SDL has a bad one (though I haven't experienced the symptom).

On my 92 300D I think I may have a bad one...though I'm still thinking through possibilities.

How do I access it? What's involved in replacing it?

Thanks.

Bio300TDTdriver · #2 07-02-2012, 10:10 AM

That is one of the only A/C related switches that I have not replaced. From the description it sounds like it is in front of the evaporator, which is not very accessible. Maybe it is accessible from the glove box if you have one on the '92. I can't recall when the passenger air bag became standard.

This is the E.T.R. sensor which senses the cabin air temperature at the evaporator. 1 per car. Limited availability.

aaa · #3 07-02-2012, 03:43 PM

I believe it's accessible from the driver's side footwell.

shertex · #4 07-07-2012, 08:42 PM

Quote:

Originally Posted by Bio300TDTdriver

That is one of the only A/C related switches that I have not replaced. From the description it sounds like it is in front of the evaporator, which is not very accessible. Maybe it is accessible from the glove box if you have one on the '92. I can't recall when the passenger air bag became standard.

This is the E.T.R. sensor which senses the cabin air temperature at the evaporator. 1 per car. Limited availability.

I don't have the air bag so maybe I could get to it.

shertex · #5 07-07-2012, 08:54 PM

Maybe this is where it is on the 92 (assuming all 124s are the same):

http://w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/Climate/83-646.pdf

Bio300TDTdriver · #6 07-07-2012, 09:01 PM

Well that seems like it should be pretty easy. I just replaced my evaporator drains, had I known that was where it was I would have taken a picture.

How much is a new one?

BTW, what are you symptoms that make you think you need new ones? Other than BC telling you that you do.

shertex · #7 07-07-2012, 09:42 PM

Quote:

Originally Posted by Bio300TDTdriver

How much is a new one?

BTW, what are you symptoms that make you think you need new ones? Other than BC telling you that you do.

$125 for a new one. On the SDL, it's BC telling me (I haven't yet experienced any symptoms). On the 92 300D, I've measured vent temps as low as 35F and, after driving for two hours or so, it doesn't cool nearly as well. So it sounds like the ETS is the culprit...but I'm open to other suggestions.

Brian Carlton · #8 07-07-2012, 11:34 PM

Quote:

Originally Posted by Bio300TDTdriver

BTW, what are you symptoms that make you think you need new ones? Other than BC telling you that you do.

The symptom is 28°F. vent temperature.

This would be "other than BC telling you that you do".

mbzjag8090 · #9 07-07-2012, 11:51 PM

Don't know about the W124 but for the W126 you can access it from the driver's side foot well. I can't recall the exact location but it is effectively right near the expansion valve...maybe a bit lower and towards the center of the car. I have experience with an 84 so the appearance might have changed by 86.

On mine it appears as a 1X1X2 inch fuzzy looking insulated thing. Kind of odd looking and soft to the touch. You can't really miss it. In a sea of plastic it sticks out. It is screwed into the HVAC box with two Phillips head screws. When you remove them pull on it and the unit will come out. It has a long wire probe that extends into the evaporator which you will feel as you remove. Don't know the symptoms when these go bad but it is not usually an issue so I would think long and hard about spending $125 bucks. Maybe try a used unit from a junkyard. If the evaporator is freezing, it definitely sounds like it could be the source of your problems.

Also, be careful when putting it back in. The two screws go directly into the HVAC plastic so thread the screws carefully.

If you are really getting 28 degree vent temps maybe you should just leave it all alone!!! That is pretty chilly

compress ignite · #10 07-08-2012, 01:46 AM

28 Degree "F" vent temps positively assure Far Below FREEZING TEMPS @ the
Evaporator.
(Hence,the lower transfer performance after protracted operation.)

Southeasterngeorgiarednecktranslation:
Y'all won't get 28 "F" vent temps for long before the evap freezes.

shertex · #11 07-08-2012, 06:57 AM

Quote:

Originally Posted by Brian Carlton

The symptom is 28°F. vent temperature.

This would be "other than BC telling you that you do".

I meant I haven't measured the SDL....just taking your word for it.

shertex · #12 07-08-2012, 07:00 AM

On the SDL, I haven't really had a problem. I can regulate the cabin temp with fan speed and vent positions. Haven't taken it on a long trip yet...first opportunity will be in August.

In fact, if it weren't for long trips, I think I really prefer the cold vent temp.

Bio300TDTdriver · #13 07-08-2012, 07:31 AM

On page 233 figure 6 there is a picture of the ETR location. It is a very large file.

Bio300TDTdriver · #14 07-08-2012, 07:37 AM

Quote:

Originally Posted by Brian Carlton

The symptom is 28°F. vent temperature.

This would be "other than BC telling you that you do".

Those vent temps are from the 124 not the 126.. Did the 126 experience the same symptoms?

I just trying to learn what the symptoms of a bad E.T.R. are, no reason to get your panties in a bunch.

shertex · #15 07-08-2012, 07:49 AM

Quote:

Originally Posted by Bio300TDTdriver

Those vent temps are from the 124 not the 126.. Did the 126 experience the same symptoms?

I just trying to learn what the symptoms of a bad E.T.R. are, no reason to get your panties in a bunch.

Brian could speak to the issue more precisely, but my recollection from talking to him is that, after some period of time (45 minutes?...Brian could tell us) vent temp would begin to rise to 50F. So apparently it would still continue to cool, just not as well. And it would only have this problem if ambient was below a certain temp. (80?) My 124 won't get as low as 28 and has the problem with a relatively high ambient.