2012 S550 AC Blows Hot On Start-Up....Fine After
Thread Starter
Member
Joined: Jun 2018
Posts: 146
Likes: 31
From: Stuart, Fl
2008 S550
2012 S550 AC Blows Hot On Start-Up....Fine After
So just like the title says my 2012 S550 blows hot air at startup with the air conditioning on but after about 30 seconds quickly starts blowing Ice Cold Air again and then it's fine for the rest of the drive. In fact it works so well it's blowing about 42° at the vent and this is in Florida heat where it's 96 degrees in the shade. I believe there's something wrong with the airbox or maybe the heater control valve where it is blending hot air with the cold air but not sure exactly how to go aboit troubleshooting cuz I'm not that familiar with the system. It doesn't do it every time but it's doing it more often than not. Any help would be greatly appreciated!
Newbie
Joined: Sep 2014
Posts: 5
Likes: 0
From: North Ft Worth TX
2012 S550, 2014 E350 & 2003 E320
I had a similar problem on my 2012 S550 for about two weeks, then it just quit blowing cold altogether.
I'm told that it's a solenoid valve mounted in the compressor itself.
Looking at the compressor ( what I can see of it. ) it's going to be a beast.
With it being a Twin turbo.... has anyone seen a "how to" on replacing that compressor?
It seems VERY close quarters.
Any tips/tricks would be greatly appreciated.
I'm told that it's a solenoid valve mounted in the compressor itself.
Looking at the compressor ( what I can see of it. ) it's going to be a beast.
With it being a Twin turbo.... has anyone seen a "how to" on replacing that compressor?
It seems VERY close quarters.
Any tips/tricks would be greatly appreciated.
Thread Starter
Member
Joined: Jun 2018
Posts: 146
Likes: 31
From: Stuart, Fl
2008 S550
Oh god....sounds like a nightmare. I had a Mercedes 190 years ago and what was happening was the blend air flap solenoid had failed and basically hot hot air from the heat exchanger was leaking and blending with the cold air but after a while it would balance out and be relatively comfortable. What I did was I actually disconnected the heat exchanger and plugged off the coolant pipes and it worked for me cuz I live in Florida and never need heat anyway but I'm hoping for permanent fix and one that will have the ability to still use Heat
Member
Joined: May 2023
Posts: 96
Likes: 53
From: California
2019 Mercedes S560
If the A/C still works, it's fine. Mine does this too - to varying lengths of time until it gets cold, but it's never longer than at most 30 seconds.
These are big cars and have big A/C systems & lots of long complex ducts for the air. My thought is all that hot air in the ducts just gets blown out. This only ever happens to me when the car is cold-started during the middle of the day when it's warmed up.
The usual first sign of the a/c not working of course is it won't get cold (duh) but if you can't go from warm to cold or change the temp at all then you have to replace this valve thing that moves to change for the desired temp. It's right under the windshield wipers I think. It's very common so 2 min of research and you will be all set.
Good luck!
These are big cars and have big A/C systems & lots of long complex ducts for the air. My thought is all that hot air in the ducts just gets blown out. This only ever happens to me when the car is cold-started during the middle of the day when it's warmed up.
The usual first sign of the a/c not working of course is it won't get cold (duh) but if you can't go from warm to cold or change the temp at all then you have to replace this valve thing that moves to change for the desired temp. It's right under the windshield wipers I think. It's very common so 2 min of research and you will be all set.
Good luck!
Thread Starter
Member
Joined: Jun 2018
Posts: 146
Likes: 31
From: Stuart, Fl
2008 S550
Oh my gosh. Brilliant! I completely forgot about that Gizmo a failing heater cintrol valve would certainly cause the symptom and it's easy enough and cheap enough to replace just on principle. I just ordered one and I will report back if it's solves the problem. Thank you!
Super Member
Joined: Dec 2018
Posts: 857
Likes: 501
From: Washington, DC
2007 S600, 2007 Chrysler 300 SRT8, 2000 C5 Corvette, 2017 Mustang GT, 2023 300C, and a 2019 Lincoln
Usually, we hear about failed water control valves on the W221 just after the first cold weather and the usual complaint is no heat. I suppose it could work also in Summer with the valve being slow to turn off the heat during A/C first puff on start up. Please let us know the outcome. I actually thought it was a blend door actuator, but I could be wrong.
Thread Starter
Member
Joined: Jun 2018
Posts: 146
Likes: 31
From: Stuart, Fl
2008 S550
Vettebk, honestly my gut tells me it's a blend air actuator as well I know there are several I believe there's also one that does air recirculation from the outside but do you know where the one is located that blends heater air with air conditioned air? I've heard they are pretty much way in the innards of the dash and requires almost a complete dash removal I can't find anything online.
Trending Topics
Super Member
Joined: Dec 2018
Posts: 857
Likes: 501
From: Washington, DC
2007 S600, 2007 Chrysler 300 SRT8, 2000 C5 Corvette, 2017 Mustang GT, 2023 300C, and a 2019 Lincoln
Take look at this even though it is more about no heat. Especially at the end is a good thing on teach in of actuators.
https://mbworld.org/forums/s-class-w...-cool-air.html
Also, but you probably have to sign up and pay was a good diagram of the dash internals.
https://www.scribd.com/document/4243...nt-Description
https://mbworld.org/forums/s-class-w...-cool-air.html
Also, but you probably have to sign up and pay was a good diagram of the dash internals.
https://www.scribd.com/document/4243...nt-Description
MB World Stories
The Best of Mercedes & AMG
6 Mercedes Models That Did NOT Age Well (But Are Somehow Still Cool)
Verdad Gallardo
Manual Mercedes? 6 Times Sindelfingen Let Drivers Have All The Fun
Verdad Gallardo
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Verdad Gallardo
8 Classic Boxy Mercedes Designs That Have Aged Like Fine Wine
Verdad Gallardo
Flawlessly Restored Mercedes 190E Evo II Heads to Auction
Verdad Gallardo
Electric Mercedes C-Class Unveiled: 11 Things You Need to Know
Verdad Gallardo
Mercedes EQS Gets A Major Update: Everything You Need to Know
Verdad Gallardo
5 Underrated Mercedes-Benz Models That Don't Get the Love They Deserve
Verdad Gallardo
Mercedes 300D Has Pushed Well Past 1 Million Miles and It Ain't Stopping
Verdad Gallardo
Thread Starter
Member
Joined: Jun 2018
Posts: 146
Likes: 31
From: Stuart, Fl
2008 S550
Well I tried something that was recommended on another site and it was to start the car and put the AC on and then cycle the temperature up to the maximum temperature and then down to the minimum temperature several times and what this does is effectively Cycles the blend air flap to fully engage and disengage. Stangely everything seems to be working well for the moment. We'll report back with any progress.
Last edited by Polo35m; Jul 9, 2024 at 08:10 PM.
Super Member
Joined: Dec 2018
Posts: 857
Likes: 501
From: Washington, DC
2007 S600, 2007 Chrysler 300 SRT8, 2000 C5 Corvette, 2017 Mustang GT, 2023 300C, and a 2019 Lincoln
Actually, doing the reset on the actuators makes a lot of sense to me also. I do this on my C5 Corvette with 24 year old technology using the little Driver Information Center (DIC) window which allows you to pull codes and reset each system (A/C being one of maybe 12 systems) from the drivers seat. When you reset A/C, you can hear the actuators fully open and close a full cycle which probably frees everything up. Keep us posted on whether exercising the actuators works.
MBWorld Fanatic!
Joined: Aug 2014
Posts: 5,322
Likes: 1,678
S500
depending on quite how cooked the car is, it means every AC car made will blow hot for a while
IR glass (an option on some 221s) will make the interior temp up to 25C cooler - without it the whole interior can easily reach 55C even in grey miserable UK - park a car in full sun for 8 hrs and it will take a 2 hr drive above 50mph to get the body panels back down to ambient.... and the whole dash and heater matrix is a glowing cooker from hell that needs significant air flow to cool down
AC in a car works just like a fridge - evaporating a liquid (in a radiator) and as this transitions into a gas it moves the heat, as the system pumps around the heat it goes to the front of the car through another rad (the condenser) to cool down and then get re-squashed by the compressor back in to a liquid - ready for round two.... because it doesn't really cool anything - it just moves heat from one location to another - they are correctly referred to as heat pumps.....
thus pumping a few hundred liters of 60C air out and moving another 20C of heat in a chemical process (of evaporation) its not an instantaneous occurrence when you turn the key
IR glass (an option on some 221s) will make the interior temp up to 25C cooler - without it the whole interior can easily reach 55C even in grey miserable UK - park a car in full sun for 8 hrs and it will take a 2 hr drive above 50mph to get the body panels back down to ambient.... and the whole dash and heater matrix is a glowing cooker from hell that needs significant air flow to cool down
AC in a car works just like a fridge - evaporating a liquid (in a radiator) and as this transitions into a gas it moves the heat, as the system pumps around the heat it goes to the front of the car through another rad (the condenser) to cool down and then get re-squashed by the compressor back in to a liquid - ready for round two.... because it doesn't really cool anything - it just moves heat from one location to another - they are correctly referred to as heat pumps.....
thus pumping a few hundred liters of 60C air out and moving another 20C of heat in a chemical process (of evaporation) its not an instantaneous occurrence when you turn the key
Thread Starter
Member
Joined: Jun 2018
Posts: 146
Likes: 31
From: Stuart, Fl
2008 S550
Just thought I would report back. I wound up replacing the heater control valve just on principle and thank goodness I did. One of the four hose nipples disintegrated in my hand just handling it and removing the clamps this would have resulted in a catastrophic coolant loss and a tow home or to the repair shop! Unfortunately this did not solve my problem at all. Its still blowing scalding hot air most of the time after the car has been driven parked and then restarted. In my mind this has to be some sort of blend air flap related issue but then again it blows Ice Cold Air after about 30 to 45 seconds and is fine for the rest of the drive. I know the blendair Works cuz I can cycle the heater on and off repeatedly and it functions correctly ice cold then scalding hot ice cold then scalding hot. So now it makes me think of another issue when I first bought the car I would go out to it and I could hear the fan running very slowly and I was told that this is normal that the car will kick the fan on to clear the duct work to keep hot air from building up and also moisture and mold from building up I never confirmed that this was true but that's what I was told. Well now it doesn't do that anymore and I've been told that it could be a failing blower motor resistor that is supposed to kick on and off to clear the ductwork. Any thoughts?
