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 hissing noise is usually from the expansion valve. If gas is enough, no leaking or bad smell just leave it. Mostly recommend to change it when you change the cooling coil as usually it is direct connected to it.

might be still under charged , and there s small leak somewhere since you heard hissing even before service

it happen when car not moving rite. notice rpm any movement or not

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.

tumpang sikit, if there's bad smell from the AC but its still cold what's the cause of it?

What kind of smell? Musty? If so got bacteria buildup inside.
Either you can buy those spray can from mr diy to clean your evaporator yourself (accessable via glove compartment)
Or
Try practice turn off ac but still on fan to let the moist dry up before you off your engine. One method is to start off your aircon when you get into your parking lot or guardhouse or etc. By the time you parked, ngam ngam time.

Hi sry to bump old thread but wta my car ac been having hissing sound for over a year already and after taking it to few mechanics and none of them could solve it, there is no leaking or no bad smell is it ok as you say to just leave it bcs ac is still cold?? I be going on a long journey soon just wta will this cause any overheating issues or other problems on the way ???

Already write mentioned if no gas leaking just leave as per it. If you rich and still so scare about it, just ask A/C shop service, flush and change the expansion valve.