If it has bubbles it means that it's low on gas.
Get it regassed (as well as vacuum leak test etc)

I had mine done 2 days ago, and now at idle it produced 8 deg C air with ambient temperature of 32 degrees C.

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Smoke Silver 1994 E220 Coupe Automatic
0 kilometers 6 September 1994
100,635 kilometers - 6 September 2010