AC temp sensor FOAM tube?? - PeachParts Mercedes-Benz Forum

dmorrison · #1 07-23-2003, 03:34 PM

Have the dash out and I noticed that the foam tube that is connected to the temp sensor is deteriating (sp). This tube was replaced about 4 years ago. The heater in the winter was irratic. and the dealer found the tube was powder and replaced it. All was well then.
Now the tube is getting in pretty bad shape. So here's my question. The tube is only 4-5 inches long and connects a hard rubber tube from the temp sensor, to another hard rubber tube that goes to the blower motor, so it can suck the interior air through the temp sensor.
So why does this soft foam tube have to be SOFT FOAM?. I want to replace it with a harder rubber tube that will last more than 4 years in the Texas heat. any comments???????????

Dave

#2 07-23-2003, 04:11 PM

What I have found is the best replacement tube is a piece of foam pipe insulation from home depot. This product has a slit lengthwise that is not completely open, so I tape around it with electrical tape, cut it to length before taping and slip it in place.

Cheap, works great and lasts forever.

Sounds like your project is moving along now.

Good luck,

jcyuhn · #3 07-23-2003, 06:14 PM

I've done what Larry recommends, and I think I also replaced one with a short section cut from an old garden hose! That won't disintegrate. Just about anything that can carry airflow and be sealed at the ends should work. This is one area in which homebrew is definately superior to factory engineered!

- JimY

dmorrison · #4 07-23-2003, 06:36 PM

Well I headed to Home Depot and found a plastic pipe that fits perfectly. Its 5/8 OD 1/2 ID H/C PEX tube. $1.88 for 5 feet ( scew 84169 48506 )I cut it to insert 1/2 inch into each tube They fit quite snug so no air will leak, I don't have to worry about it slipping out. Its also a very rigid tubing and looks like it will not deteriorate. The attached photo shows the new tube installed. Below the white replacement tube is the old foam tube
Notice the black and blue on the thumb, got that working on the SDL. Adjusting the toe-in toe-out and the jack got me!!!

The AC is comming along but slowly, I wish it was done, but with the heat here in Texas I don't feel like working on the car. I really have no excuse since I have a AC in the garage and it can actually be quite comfortable when I let it cool things off for 30 mins or so. I will get it done eventually. Actually its probably the summer cold that I have. Iv'e been off work a couple of days, couldn't get the ears to equalize so I didn't want to fly and rupture an ear drum.

Dave

Palangi · #5 07-23-2003, 09:09 PM

Dave

I used a hunk of clear vinyl tubing to replace the foam aspirator hose. Your plastic tubing will work fine. You may want to take a look at the evaporator drain hose, as it's made out of the same foam material. When that one goes, it will fill the rear seat footwells with water.

timreid · #6 07-23-2003, 09:25 PM

Dave could you please tell me were the foam tube connecting to temp sensor is located behind the dash, I have a 400E, and I would like to change the foam tube.

Enjoy your drive, timreid

dmorrison · #7 07-23-2003, 11:56 PM

timreid
I am not familiar with the 400E. And do not know if or where a foam tube on your car would be.
Maybe someone else on the forum knows!!!!!!!

Dave

#8 07-24-2003, 06:34 AM

There are many materials that will serve to carry the air to the sensor, but there is a very important reason for using foam tubing. The foam tubing will conduct very little heat through the wall of the tubing. This way you get a MUCH more accurate air sample to the sensor. Vinyl, plastic or other materials will cause the sensor to measure the temperature of the hose, rather than the temperature of the air sample going through the hose.

This is why MB put a foam hose on it in the first place. They just didn't have a very durable material.

Have a great day,

wjm · #9 07-24-2003, 07:10 AM

OK,

I'm a bit confused. As reported on another thread, I have water settling in the front passenger footwell of my vehicle. After taking out the side piece next to the radio, I can feel the a foam piece that is deteriorating. I am assuming that this is some sort of drain hose that is leaking.

Above, though, folks are calling this A/C temp sensor related. I thought that the A/C temp sensor was above inside the domelight and uses the aspirator motor (behind passenger dash) to pull air across it.

If that's the case, then why would they have used foam in my car?

I ordered some new tubing from Phil here at Partshop (it's cheap)... but may just find some stronger material if its the better way to go.

timreid · #10 07-24-2003, 07:27 AM

Willy, That is the AC drain, there is one on each side. And yes just go to your auto or hardware store and buy rubber or vinyl tubing for replacement, a much better repair than using the foam tubing.
Enjoy your drive, timreid

wjm · #11 07-24-2003, 07:34 AM

Thanks!

How much of the vehicle needs to come out in order to replace properly?

timreid · #12 07-24-2003, 09:34 AM

If I remember correctly I removed: HVAC wood panel cover, the center console, and the side carpet pieces. And I'm not sure about the lower dash panels, but you'll find out if that necessary.

enjoy your drive, timreid

wjm · #13 07-24-2003, 09:41 AM

Thanks Tim.

When you say center console, do you mean removing the ashtray, radio, shifter wood and then entire center plastic piece (about 3 ft long)??

Thanks!

jcyuhn · #14 07-24-2003, 10:00 AM

Larry -

On a 123 the thermister which measures air temperature is located at the base of the through-the-dash plastic fitting. It's about 1/2 inch below the air intake grille. By the time the air transits the foam/pvc/garden hose tube, it has already been measured. So I don't think the actual material matters very much.

Why did MB choose open cell foam? Probably because it's lightweight, cheap, and easy to install.

- JimY

#15 07-24-2003, 10:01 AM

Okay, let's be clear here. The thread was started by dmorrison who I happen to know is working on a 123 car. The temp sensor location and sample air tube routing is TOTALLY different from that of a 124 car.

Hope this helps,