HVAC blend door actuator replacement
Thread Starter
Junior Member
Joined: Dec 2022
Posts: 56
Likes: 13
2012 MB R350 Bluetec
HVAC blend door actuator replacement
My 2012 R350 bluetec has an issue:
1. The passenger side vents, rear, and front windshield vents will not blow HOT air.
2. The AC for ALL vents is cold and is perfect
3. The driver side HEAT is perfect
4. Blower fan is perfect, no issues.
So I am suspecting there is an issue with the blend door actuators. I would like to replace them. I see from eBay that they come in a package of 5 or 6. One of these must be the blend door actuator for the HEAT. Does anyone have instructions and information to help me replace the blend door actuator for heat?
Thank you.
1. The passenger side vents, rear, and front windshield vents will not blow HOT air.
2. The AC for ALL vents is cold and is perfect
3. The driver side HEAT is perfect
4. Blower fan is perfect, no issues.
So I am suspecting there is an issue with the blend door actuators. I would like to replace them. I see from eBay that they come in a package of 5 or 6. One of these must be the blend door actuator for the HEAT. Does anyone have instructions and information to help me replace the blend door actuator for heat?
Thank you.
Member
Joined: May 2010
Posts: 89
Likes: 8
From: Gautier Ms
2008 R350, 2024 Subaru Legacy,2018 Chevy Colorado
I believe there are two blend actuators/motors.....left and right. They must be "learned" after being replaced using a diagnostic tool. I have replaced the left one on our R a few years back. Fairly easy job.
Left side is above accelerator pedal and right side is left upper passenger footwell.
Left side is above accelerator pedal and right side is left upper passenger footwell.
Thread Starter
Junior Member
Joined: Dec 2022
Posts: 56
Likes: 13
2012 MB R350 Bluetec
I believe there are two blend actuators/motors.....left and right. They must be "learned" after being replaced using a diagnostic tool. I have replaced the left one on our R a few years back. Fairly easy job.
Left side is above accelerator pedal and right side is left upper passenger footwell.
Left side is above accelerator pedal and right side is left upper passenger footwell.
Yes, I took the glove box off and could see a blend door actuator underneath the blower fan. Did you have the same symptoms as me? I wonder if replacing it will help fix my issue.
Member
Joined: May 2010
Posts: 89
Likes: 8
From: Gautier Ms
2008 R350, 2024 Subaru Legacy,2018 Chevy Colorado
A diagnostic tool that will cycle the actuators and test the ACC would be most helpful and keep you from throwing parts at the problem....failed temp sensors in the vent ducts will also give problems as you described.
Newbie
Joined: Jun 2025
Posts: 13
Likes: 3
2012 Mercedes R-Class R350 CDI 265HP Long
I might be mistaken though.
Newbie
Joined: Jun 2025
Posts: 13
Likes: 3
2012 Mercedes R-Class R350 CDI 265HP Long
Usually, if it is just clogged, you can connect a hose to it, and pour a mixture of Hot water and dishwasher powder into it, let it cool down, and use a garden hose to flush out the crud.
Or follow a guide like this: https://www.cleaningbasic.com/how-to-clean-heater-core/
The heater core, is just a radiator. Are you referring to the whole heater box?
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Thread Starter
Junior Member
Joined: Dec 2022
Posts: 56
Likes: 13
2012 MB R350 Bluetec
Update:
Issue solved.
1. Mechanic was about to replace the heater core, when he decided he would flush it out first.
2. Good on him to start with flushing, a HUGE amount of silicone based junk came out of the heater core. The silicone was blocking the heater core. He spent 1.5 hours properly cleaning the heater core. He verified that it was clean using an endoscope. Heat is back to perfect.
3. Mercedes installs a permanent silica gel bag in the coolant reservoir. It is embedded in it. Over time, this bag can breakdown and send silica particles all throughout the coolant system, and they love to lodge in the heater core for some reason.
I am happy to have heat back and hopefully others can also attempt flushing before jumping to replacement.
Issue solved.
1. Mechanic was about to replace the heater core, when he decided he would flush it out first.
2. Good on him to start with flushing, a HUGE amount of silicone based junk came out of the heater core. The silicone was blocking the heater core. He spent 1.5 hours properly cleaning the heater core. He verified that it was clean using an endoscope. Heat is back to perfect.
3. Mercedes installs a permanent silica gel bag in the coolant reservoir. It is embedded in it. Over time, this bag can breakdown and send silica particles all throughout the coolant system, and they love to lodge in the heater core for some reason.
I am happy to have heat back and hopefully others can also attempt flushing before jumping to replacement.
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Thread Starter
Junior Member
Joined: Dec 2022
Posts: 56
Likes: 13
2012 MB R350 Bluetec
Update:
1. Heater core flush only fixed the heat temporarily for about 1-2 months
2. We decided to go ahead with full heater core replacement. An important note, we bought an aftermarket heater core from rockauto to save costs, but got screwed because the aftermarket heater core was incompatible with the factory heater core hoses. So we had to pay up for an OEM heater core (about $400 CAD), and then my mechanic undertook the herculean task, which was about 10-12 hours of labour.
3. I can confirm that heater core replacement has fixed the issue. There is heat in the front and back and both sides of the car now.
1. Heater core flush only fixed the heat temporarily for about 1-2 months
2. We decided to go ahead with full heater core replacement. An important note, we bought an aftermarket heater core from rockauto to save costs, but got screwed because the aftermarket heater core was incompatible with the factory heater core hoses. So we had to pay up for an OEM heater core (about $400 CAD), and then my mechanic undertook the herculean task, which was about 10-12 hours of labour.
3. I can confirm that heater core replacement has fixed the issue. There is heat in the front and back and both sides of the car now.
Update:
Issue solved.
1. Mechanic was about to replace the heater core, when he decided he would flush it out first.
2. Good on him to start with flushing, a HUGE amount of silicone based junk came out of the heater core. The silicone was blocking the heater core. He spent 1.5 hours properly cleaning the heater core. He verified that it was clean using an endoscope. Heat is back to perfect.
3. Mercedes installs a permanent silica gel bag in the coolant reservoir. It is embedded in it. Over time, this bag can breakdown and send silica particles all throughout the coolant system, and they love to lodge in the heater core for some reason.
I am happy to have heat back and hopefully others can also attempt flushing before jumping to replacement.
Issue solved.
1. Mechanic was about to replace the heater core, when he decided he would flush it out first.
2. Good on him to start with flushing, a HUGE amount of silicone based junk came out of the heater core. The silicone was blocking the heater core. He spent 1.5 hours properly cleaning the heater core. He verified that it was clean using an endoscope. Heat is back to perfect.
3. Mercedes installs a permanent silica gel bag in the coolant reservoir. It is embedded in it. Over time, this bag can breakdown and send silica particles all throughout the coolant system, and they love to lodge in the heater core for some reason.
I am happy to have heat back and hopefully others can also attempt flushing before jumping to replacement.
