Locating and replacement of heat blend door actuator

1997 MERCEDES BENZ S420

194,000 MILES • 4.2L • V8 • 2WD • AUTOMATIC

JAMESDEANFISHER

MEMBER
1 POST

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

Dec 29, 2018 at 9:03 PM

JACOBANDNICKOLAS

✓ASE Certified Mechanic
110,193 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

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Dec 30, 2018 at 9:46 PM

Repair Safety Notice: This information is for general instructional purposes only. Vehicle repair can be dangerous. Verify all information, follow manufacturer service procedures, use proper tools and safety equipment, and consult a qualified repair shop when needed.