AC temp sensor FOAM tube?? - Page 2 - PeachParts Mercedes-Benz Forum

dmorrison · #16 07-24-2003, 11:56 AM

Larry
I agree with the philosophy that the foam will not transmit heat and give a false reading. but the tubing is downstream of the sensor. I think they used the foam for remove and replace ability. Even though you have to glue the foam piece. It may be easier to work with when going through the glove box to replace it. I 'm not sure. The photo below shows the entire tube assembly. does that section go by the heater core and is subject to heat? If so would it really make a difference in the sensor reading? Or did they anticipate that the hose would deteriorate at this location due to the heater core location? I really don't know and I'm grasping at straws here. So The car will now have the plastic tube and in 10 years I'll find out why they did this. I'll probably have to take the dash out again to replace the tubing instead of just doing it throught the glove box.

Dave

#17 07-24-2003, 12:20 PM

Yes, it's a 15 minute job to replace it by removing the glovebox.

Good luck with your project,

RunningTooHot · #18 09-09-2003, 10:59 AM

The factory used thick insulation because the under-dash temperatures can be VERY different from that in the cabin – if you use a piece of non-insulated tubing, the sensor will sometimes pick up the under-dash temperatures if the car is parked for a short time. This can lead to some pretty strange symptoms in extreme weather.

For example, when it is hot out and you use the AC for a good while, the temperature underneath / inside the dash can become pretty cold. Park the car for 5-10 minutes under these circumstances and the cool temperature will soak through a non-insulated tube and reach the sensor. When you go back to start the car, it will sense a very cold condition and blow hot air at you for a minute or two until the sensor warms back up. NOT a fun thing in 90-100 degree weather. Ask how I know this…

dmorrison · #19 09-10-2003, 03:21 AM

RunningTooHot

I understand your logic. But if your idea is true then why is the rest of the black tube from the sensor to the motor black solid tubing.
Look at the picture above. The White tube is connected to two long black tubes.
First.
The sensor is at the intake section of the tube. It is located at the center top of the dash. Just above the 2 outlets.
Second.
The tube goes along the inside of the dash, past the glove box and is connected to the "intake" section of the blower motor. The tube is designed to pull air over the sensor. The sensor is 1/2 an inch from the intake. So I don't see where the "temp" build up or cool down would effect the system temperature input.

Dave

erubin · #20 09-10-2003, 08:44 PM

I too replaced the disintegrated hose with pipe insulation. Reading dave morrison now has me convinced that any hose that fits correctly mechanically would have worked because the sensor is up stream from the hose! Whether the hose is insulated or not should make no difference.