Polo35m

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!

Frustration_X_2

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.

Polo35m

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

justchangeoil63

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!

Polo35m

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!

vettebk

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.

Polo35m

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.

vettebk

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

Polo35m

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.

vettebk

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.

BOTUS

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