Benz C320 AC / Air Conditioner Trouble – Warm at Idle


Hi everyone….I have a 2003 C320 and have had this problem for some time and looking for some assistance. When I first start my car the AC will only blow warm air.
Benz C320
I was recently low on freon and had the hissing sound so charged it to the high amount to about 45lbs on the gauge–the max green. Before charging it was in the middle of the green range why I put it up at the max. Anyhow this was after driving it for some time and it blew cold while at idle and the pressure on the Climatic Control Diag #7 remained steady.

Next day I start my car and the Diag #7 showed about 30!! Put the gauge on and it showed extremely high. Well figured it worked the night before so would drive it and see what happens. Before my car operating temp warmed up I watched the number fluctuate and drop while I was driving and then rise when I was not moving at idle. It would kick the AC compressor off when it reached 31ish drop the pressure to about 29 then kick back on and cycle like that until I started driving again.

After the car warmed up to normal operating temperature it seemed the reading on the climatic control would not go above 20 and while driving went down to 10.

Is there something that will cause the pressure to rise when the car is not driving? I am not sure if it’s directly correlated to the operating temperature of the engine but does seem to be better when the car is warmed up.


Here are the readings from my climatic; don’t know how to pull any error codes but none in MB STAR DAS.

warm air-
00 84
01 84
02 86
03 75
04 75
05 78
06 201
07 31
08 194

Cold air
00 82
01 82
02 86
03 75
04 75
05 82
06 206
07 11
08 143



If you used that DIY freon kit your not helping take it to a shop where they have the proper equipment to service that system. You can blow a line overcharging it.
It seems that its low if the compressor is kicking off there may not be enough in the system to compress.
Ideally the ac equipment will give precise readings for the psi and see of there is a leak.
If there is enough in the system and the compressor is kicking on and off abnormally then the compressor is going out.
Had this issue in my AMG and I’m a tech so just my 2cents.


The pressures in the condenser getting up to 30bar is a bit alarming. There is definitely something wrong, don’t add anymore gas!┬áCharging by pressure alone is very difficult for models with a variable compressor. You most likely have overcharged the system which is giving the very high pressures. I would suggest you get it evacuated, vac’d down and recharged properly. If the problem persists then you may have a sticking TX valve.

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