The air conditioner in my car is acting "as designed" or maybe the clutch is "sticking" and refusing to let go of the compressor, so I can't figure out how to turn it off.
It is a 2014 C180 S204 (a German car) with the license plate OM651.
A few specifics:
The air conditioner is flawless; the speed of the cabin fan increases automatically upon activation and decreases upon deactivation, and the light on the AC button illuminates properly. All of the HVAC controls are turned off or set to manual, and the temperature is completely cold on both sides.
Issue at hand:
The air conditioner continues to blow extremely cold air for several minutes after I turn it off, regardless of how briefly it was on.
I conducted this empirical test yesterday:
After 20 minutes of driving with the air conditioning on "front and feet" and the fan set to maximum speed, the car's temperature had stabilised.
With the outside temperature at 36°C, I was travelling at a speed of approximately 80 km/h, or around 1500 rpm.
In order to catch the blast from the left side vent, I had my left hand open and resting on the steering wheel. As soon as the air was no longer cold, I turned on the air conditioner. After approximately 5 seconds, the air temperature dropped again, so I turned the air conditioner off again while keeping the fan speed set to maximum. The fan speed slowed down slightly after turning off the air conditioner, but that was par for the course.
The air emitted was chilly for the first seven minutes, but it warmed up fast after that.
This begs the question:
It appears like the compressor was running the entire time the cold air was being expelled. Is this the intended behaviour or am I totally mistaken and the evaporator can be cooled down to the point where it takes seven minutes to heat up again after just five seconds of running?
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Resetting the flap motors from the dashboard is a common solution when you are unsure of the proper operation of your air conditioner's vents. The 204 procedure is something I don't know, but I'm sure someone here or in the manual can fill you in.
Assuming it is a variable swash plate compressor—like the one on my 203—the air conditioner keeps turning as long as the engine is running; the pressure regulator simply adjusts the plate's angle.
So, there's no fuss. When was the last time you changed the cabin filter? Also, has the system pressure been checked lately?
Assuming it is a variable swash plate compressor—like the one on my 203—the air conditioner keeps turning as long as the engine is running; the pressure regulator simply adjusts the plate's angle.
So, there's no fuss. When was the last time you changed the cabin filter? Also, has the system pressure been checked lately?
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That is helpful information; I have been and will continue to be quite busy with home improvement projects, so I have not had much time to learn about cars.
If you turn the air conditioner on, you won't notice a decrease in engine speed, and this is why.
I should have changed the cabin air filter when I got the car a few months ago, but the air conditioning is really cold, so it's good. Can I use a scan tool to see the compressor's output? (Once I make up my mind, I will definitely purchase one.)
If you turn the air conditioner on, you won't notice a decrease in engine speed, and this is why.
I should have changed the cabin air filter when I got the car a few months ago, but the air conditioning is really cold, so it's good. Can I use a scan tool to see the compressor's output? (Once I make up my mind, I will definitely purchase one.)
Posts: 73
Joined: Mon Apr 06, 2026
Posts: 73
Joined: Mon Apr 06, 2026
Many specialists use this "scan tool" to check if the air conditioner is working properly through multiple vents simultaneously. 
A low-cost method of performing a system check on your own. I purchased a pair of them online for approximately £12 not long ago.
A low-cost method of performing a system check on your own. I purchased a pair of them online for approximately £12 not long ago.
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Joined: Mon Apr 06, 2026
For the purpose of understanding why the swash plate "actuator" takes a little longer to return to "no pressure required" than it should, or if it's simply the nature of this AC, I'm more curious about the difference between the "refrigerant pressure" that is actually applied and the pressure that is demanded.
Presumably, engine rpm also affects the compressor output.
The vehicle is still under warranty, so if anything goes wrong (and I have the paperwork to back it up), the repair should be on the house.
Presumably, engine rpm also affects the compressor output.
The vehicle is still under warranty, so if anything goes wrong (and I have the paperwork to back it up), the repair should be on the house.
Posts: 73
Joined: Mon Apr 06, 2026
There is no direct relationship between engine speed and air conditioning pressure; rather, the pressure is changed regardless of engine speed (within reasonable limits) by adjusting the swash plate angle to meet demand.
Here we have the convoluted explanation. You can find a lot of videos on YouTube.
Here we have the convoluted explanation. You can find a lot of videos on YouTube.
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It is quite typical for cold air to continue blowing for several minutes after turning off the air conditioner, although I am not sure about seven minutes. It seems like the air conditioner is being turned down slightly. When I'm more than a mile away from home, I turn off the air conditioner to prevent musty odours by drying out the evaporator. Even for the final mile, the wind is chilly.