Locating and replacement of heat blend door actuator

JAMESDEANFISHER

MEMBER
1997 MERCEDES BENZ S420
4.2L
V8
2WD
AUTOMATIC
194,000 MILES

I have no heat. When I change modes, nothing changes, no heat. I changed the thermostat thinking that was the problem, not so. I am now looking for the heat blend door. I will change that out. Seems nothing else can be the problem since all else works fine.

Many thanks and happy New Year!
James Dean
copywriter/journalist

1 Reply

JACOBANDNICKOLAS

MECHANIC
109,758 POSTS

Hi and thanks for using 2CarPros.

On your vehicle, the temperature (blend air door) is actuated by engine vacuum. With that in mind, before replacing anything, confirm there is not vacuum leak.

Next, the blend flap vacuum elements (45, 46) are located on the air conditioning housing. That is where you have to check to see if there is a problem.

I have attached pictures to help, but they are complicated. Start by locating items 45 and 46. Confirm there is vacuum available to them and then determine if they are opening and closing the blend flap.

Take care and let me know if you have other questions.

Joe

Image (Click to make bigger)