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85 Merc 300D - Unwinding 31 years of wear
86 VW TD
Mahindra Diesel
Iseki Diesel

In 2007 I didn't own a diesel.

The cabin temperature sensor lives under that little vent. It talks to the climate control system, tells it how warm the cabin is. A hose leading to the blower pulls air through the vent so that the sensor reacts better and more quickly to temperature changes.

The dash-mounted sensor is somewhat sensitive to warming from sunlight and the tube leading to the blower has a foam section that disintegrates over time. If one of the wires to the sensor breaks or comes loose the climate control system will not work correctly. If I remember right, it will go into "all the way hot" all the time unless you move the temperature wheel all the way into the click-stop on the blue (cold) side.

More than you wanted to know? Sorry!

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

That is almost perfect information Jeremy.

My car is either very hot or not. I have to put it on 18 degrees to keep from roasting on a road trip tonight. I thought that the vents were going to melt.

Do you think that I should try blowing some air down through there to start. Might be a dead bug or something?
Can I just pry off the grill?

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85 Merc 300D - Unwinding 31 years of wear
86 VW TD
Mahindra Diesel
Iseki Diesel

In 2007 I didn't own a diesel.

i will also note that the "air jet" system that pulls air over the vent can fail down at the blower motor. there are some rubber hoses there that can degrade because they are exposed to a vent to the outside. if you fix the foam hose and still aren't getting airflow over the sensor, check down at the blower too.

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1981 NA 300D 310k miles

You could try blowing in the vent just in case it's blocked with dirt but I suspect you'll want to remove the glove box liner so you can look inside to check on the two wires to the sensor and also see to the hose that pulls air past the sensor. I think it's also possible to look into the vent with a small powerful (LED?) flashlight and see the sensor. It's a little blob the size of an aspirin. The little grille cannot be pried out -- it's locked from the underside. All you'll do is break it!

The glove box liner pulls out after you pop the little plastic holders and remove the hook on top that the latch engages (2 Phillips screws). The plastic pins are actually in 2 pieces each. Pry up on the center pin carefully with a dull knife and it will come out. The outer part can then be pried out. There are three or four at top and more on the bottom. You'll also have to remove the light fixture, which pries down at the part closes to the lid (door) of the glove box. Pull the fixture out and remove the wires.

Jeremy

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970