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2012 C250 W204 167K -- My AC blows cold for the first 15 minutes or so while driving then blows warm? It'll do this off and on for the duration of the drive. I have refilled the freon so it is not low. Not sure where to start troubleshooting? Any feedback would be appreciated. Thanks!
2012 C250 W204 167K -- My AC blows cold for the first 15 minutes or so while driving then blows warm? It'll do this off and on for the duration of the drive. I have refilled the freon so it is not low. Not sure where to start troubleshooting? Any feedback would be appreciated. Thanks!
First of all: how old is the cabin filter ???
Can you read the refrigerant pressure ?
Compressor prop valve may be ready for replacement.
Over charged almost as ineffective as low. Normally circuit is charged precisely by weight with a scale.
Last edited by CaliBenzDriver; Mar 31, 2026 at 01:01 PM.
Do you have a Mercedes specific obd scanner to be able to see the refrigerant pressures? It also can show evaporator sensor temp as well as currents when the compressor cycles on and off. My scanner was very important in diagnosing my issue. Mine was basically low on refrigerant so i added a little more. With the scanner and the refrigerant gauge I was able to make sure it was not over filled, which would cause issue.
Hook up the scanner and read the pressure when off then when running. Mine also will show any fault codes. Has a function test for the compressor. oddly enough my scanner said it was not underfilled, which it actually was but just by a little. i ended up putting in 1/2 can of straight refrigerant, I dont recommend using a refrigerant with a sealer in it.
Mine was showing around 1.9 bar on the scanner, the low pressure gauge was showing low when running So I filled it until it was around 11 bar running.
Thanks for all your replies! All these years working on cars it didn't even dawn on me to plug in the scanner and check. lol. No check engine light so didn't even think about it. Here's what I found when checking with the scanner. I assume the actuator is the problem?
Last edited by broncosdom; Apr 2, 2026 at 11:06 AM.
Reason: typo
You seem to have good refrigerant pressure and the evap temp sensor shows it is getting cold.
With your obd scanner can you actuate and function test each motor? Mines under actuator motors in the hvac section.
I have a 2010 so not sure how different a 2012 is. Under the hood remove the plastic box above the battery. The blower motor is in there in mine. Right before it is a door that opens and closes, mine will cycle itself when unlocking the doors performing a function test. When the door is open you can look in the back and see a honeycomb looking vent, thats where the recirculated air goes into the vents from behind the glove box.
It may be one of the two motors that operates these doors. Located inside behind the glove box.
Hello, I removed the battery cover and was able to cycle open and close the door above the fan without any problem. My scanner does not have the ability to actuate each motor one at a time. I was able to look them up one by one. There was only 1 that had different readings than the others.
Actuator motor M16/22 showed 'position of actuator motor specified by the control unit 74%' all other actuators at the time showed 0%. Not sure what that means?
Im not really sure what those current flap and stored flap adjustment range means.
The position 74% and Current position 73.98% looks right, im guessing the computer wants it at 74% and its showing at 73.98%.
I had to look up what the M16/22 even is:
I made a mistake in one of my comments above. I was confused with seeing the 18 degrees not realizing its Celsius. With your scanner hooked up turn the ac on full and see how low the evap temp drops. When I was working on my ac I was seeing it down to 2 Celcius/ 35 F. if the evap temp does go down to freezing we know the ac compressor is working. If the temps do go low try going for a drive with the scanner hooked up so you can see the evap temp. If the evap temp stays cold but warm air starts coming out then we can see if it triggers an actuator fault.
I hooked up the scanner to check out that reading -
This is at idle in the carport with the AC on high for approx. 5 min
This is with the scanner hooked up while driving approx. 10 minutes
This is back in the carport after driving sitting idle for about 5 minutes
The air blew cold during and after the drive...I erased the DTC code before the drive it did not return. I'll try again tomorrow to see if it throws the code again. Thanks!
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