Heating system help
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Newbie
Joined: Oct 2019
Posts: 9
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W220 S500 2002
Heating system help
so i have had my S class 2002 for the summer so far and 0 issues with the aircon, but now when the temperature is dropping im finidng myself having issues
so to go in to detail
when im trying to warm up the car the middle air vent is not on whatsoever (its turned to auto) and the ones in the door is "barly" puting out ANY air at all but they at least are, the defrost vent in the front works and not works at the same time, its the only vent showing air in to the cabin, but its shooting COLD air!!!! also if i turn off auto on the centre airvents in the front they turn on like normal but they are just like the window vent shooting COLD air
this is a problem as long as the system is set to a higher temperature than there is inside aka its supposed to heat. is the temperature is set to less than the outside temperature the aircon turns on and all the vents start up no problem but its still cold as the temperature is set to cold.
meanwhile i have the long wheelbase version and a independent system in the rear and those 2 in the centre for the rear seats is like a tornado of WARM air, in other words the rear vents works flawlessly without any issue
any help with this would be much appriciated
(by cold air i mean like same temperature as outside or maybe 1 degree celsius more but not noticable)
so to go in to detail
when im trying to warm up the car the middle air vent is not on whatsoever (its turned to auto) and the ones in the door is "barly" puting out ANY air at all but they at least are, the defrost vent in the front works and not works at the same time, its the only vent showing air in to the cabin, but its shooting COLD air!!!! also if i turn off auto on the centre airvents in the front they turn on like normal but they are just like the window vent shooting COLD air
this is a problem as long as the system is set to a higher temperature than there is inside aka its supposed to heat. is the temperature is set to less than the outside temperature the aircon turns on and all the vents start up no problem but its still cold as the temperature is set to cold.
meanwhile i have the long wheelbase version and a independent system in the rear and those 2 in the centre for the rear seats is like a tornado of WARM air, in other words the rear vents works flawlessly without any issue
any help with this would be much appriciated
(by cold air i mean like same temperature as outside or maybe 1 degree celsius more but not noticable)
Super Member
Joined: Dec 2007
Posts: 980
Likes: 225
2005 S500 Designo
HAh; welcome to S-Class ownership
Although it might be some flaps in the HVAC system, more likely than not it's the duo valve:
Mercedes has a feature where instead of using the engine coolant pump to circulate coolant into the cabin, they have a separate electric pump commonly called a "duo valve" b/c the assembly has two valves.
They seem to all go bad, so used parts don't work. It's underneath your windscreen wipers, and you likely have to replace it. It's possible only the valves are stuck; you can open up the valves and remove any crud with just a Phillips screwdriver. You can test the valves themselves with some 12v leads. Likely you'll also need
Here's the part #: 2208300084
Here's a video on how to replace it:
I might be wrong, so I'd double check. There's a secret menu in the A/C system that can give you more info incl. fault codes, if one of your flaps is stuck. That could also get you your symptoms
Although it might be some flaps in the HVAC system, more likely than not it's the duo valve:
Mercedes has a feature where instead of using the engine coolant pump to circulate coolant into the cabin, they have a separate electric pump commonly called a "duo valve" b/c the assembly has two valves.
They seem to all go bad, so used parts don't work. It's underneath your windscreen wipers, and you likely have to replace it. It's possible only the valves are stuck; you can open up the valves and remove any crud with just a Phillips screwdriver. You can test the valves themselves with some 12v leads. Likely you'll also need
Here's the part #: 2208300084
Here's a video on how to replace it:
I might be wrong, so I'd double check. There's a secret menu in the A/C system that can give you more info incl. fault codes, if one of your flaps is stuck. That could also get you your symptoms
Last edited by Fried Chicken; Nov 23, 2019 at 02:01 AM.
