Just sent my car for AC flushing yesterday as preventive maintenance.

But after the flush, I could hear some hissing noise from the aircon vent (probably dashboard). The noise came out:
1. Few seconds when the compressor kicks in.
2. Also few seconds when compressor stops/after shutting off the engine.

Went back to the workshop again this morning and they ran through the AC system using the AC service machine. Pressure and air outlet vent temperature is normal. They couldn't identify why the hissing noise is there, but at least the hissing noise is little bit softer compared to yesterday.

Cooling coil and expansion valve also changed not so long ago, like 3 years back.

I know the hissing noise is there since day 1, but it was very faint until the AC flushing ytd. Anyway, The AC is still as cold as before.

Is this normal? Or I should send to other places for checking?

The cooling coil and exp valve changed together 3 years ago, and so far so smell and AC still cold. Just some faint hissing noise on and off.

Thought about that, but right before flushing they checked my pressure and said the pressure was ok. Haven't top up any refrigerant for the past 3 years also. Shouldn't be any leak i guess.


I think it happens like on and off whether its moving or not, just that it is more apparent when the car is station coz no road noise. RPM is quite normal with the compressor on and off.