Heat all the time & vent control problems
Thread Starter
Junior Member
Joined: May 2021
Posts: 15
Likes: 1
beta 390rrs. 2010 GL550
Heat all the time & vent control problems
Hi All.
I have had an issue with my 2010 GL550 HVAC system for quite a while and have been "working around" it until a recent trip to the mechanic. A lot to read here so grab a coffee. Thanks in advance for your insights/ideas.
Previous problem: Heating works fine UNTIL the temperature set point is reached (eg. 76 on the dial) on the drivers side. THEN the system will add too much cold air and all vents run cold on drivers side only. (Passenger side works perfectly). This happens in Auto or manual control mode. The work around is to set drivers side to max heat. This is temporary as Max does seem to have some temp control set point where cold is brought in again. This is really only a big issue when crossing mountain passes in winter and needing full heat on the drivers side to keep snow cleared on windshield. I could run the dial cold then hot, turn system on/off to regain control of heat. One interesting note here is that when in manual mode, adding floor to defrost and vents would cause it to run cold air to floor immideately
Previous troubleshooting: Mercedes scanned my car on 2x visits to address the brake booster recall. they also updated the car SW for HVAC and did a relearn/reset on vents. No codes present and no change to how the system was working.
My local Mercedes independent found a bulletin similar to this issue and ran a series of tests to see if we can solve. There were no codes present and the system functioned as expected via DAS.
The exercising of the system has essentially made it worse and not identified what in the system is malfunctioning.
New Problem: Now the drivers side blows MAX HEAT all the time regardless of any temperature setting on the dial. In Auto setting it will just blow hot until I have to escape or open all the windows. In manual I can add floor to vents or vents+defrost and it will run cold. I am now in a purgatory of system on/off and then floor on/off to maintain drivers side temps. One interesting observation is that while in Manual and Vents are selected, heat will blow out the foot vents. When I select floor vents, it will immediately blow cold. Video here. https://photos.app.*******/ABbjo5N3m7Byb4M19
Passenger side works perfectly. Heat and cools as expected. Issue is only on Drivers side.
Our current theory is either the control module or flapper/blend motors are not functioning but also not sending codes. I am hesitant to make any investment in this vehicle as pulling the dash out to replace parts blindly could be huge waste of time and $$.
Anyone else have this problem and solve it?
Thoughts suggestions?
I have had an issue with my 2010 GL550 HVAC system for quite a while and have been "working around" it until a recent trip to the mechanic. A lot to read here so grab a coffee. Thanks in advance for your insights/ideas.
Previous problem: Heating works fine UNTIL the temperature set point is reached (eg. 76 on the dial) on the drivers side. THEN the system will add too much cold air and all vents run cold on drivers side only. (Passenger side works perfectly). This happens in Auto or manual control mode. The work around is to set drivers side to max heat. This is temporary as Max does seem to have some temp control set point where cold is brought in again. This is really only a big issue when crossing mountain passes in winter and needing full heat on the drivers side to keep snow cleared on windshield. I could run the dial cold then hot, turn system on/off to regain control of heat. One interesting note here is that when in manual mode, adding floor to defrost and vents would cause it to run cold air to floor immideately
Previous troubleshooting: Mercedes scanned my car on 2x visits to address the brake booster recall. they also updated the car SW for HVAC and did a relearn/reset on vents. No codes present and no change to how the system was working.
My local Mercedes independent found a bulletin similar to this issue and ran a series of tests to see if we can solve. There were no codes present and the system functioned as expected via DAS.
The exercising of the system has essentially made it worse and not identified what in the system is malfunctioning.
New Problem: Now the drivers side blows MAX HEAT all the time regardless of any temperature setting on the dial. In Auto setting it will just blow hot until I have to escape or open all the windows. In manual I can add floor to vents or vents+defrost and it will run cold. I am now in a purgatory of system on/off and then floor on/off to maintain drivers side temps. One interesting observation is that while in Manual and Vents are selected, heat will blow out the foot vents. When I select floor vents, it will immediately blow cold. Video here. https://photos.app.*******/ABbjo5N3m7Byb4M19
Passenger side works perfectly. Heat and cools as expected. Issue is only on Drivers side.
Our current theory is either the control module or flapper/blend motors are not functioning but also not sending codes. I am hesitant to make any investment in this vehicle as pulling the dash out to replace parts blindly could be huge waste of time and $$.
Anyone else have this problem and solve it?
Thoughts suggestions?
Thread Starter
Junior Member
Joined: May 2021
Posts: 15
Likes: 1
beta 390rrs. 2010 GL550
Hi Max. I have not done that. Not sure what effect that would actually have. Can you explain?
The HVAC system has been forced to relearn/zero all the vent motors several times though.
The HVAC system has been forced to relearn/zero all the vent motors several times though.
