Hissing with key in the on position but engine off.

Sf3500 · Post by **Sf3500** » 03 Aug 2019, 02:54

Just recently, I have noticed the car begins to hiss and release a gas of some sort into the cabin, I say it's a gas because it is often accompanied by harsh cough and watery eyes.

What could this hiss possibly be. The gas is odorless and colorless. Here is a video of the hissing noise. Can somebody please help me identify where the hissing is coming from. Keep in mind the climate control system is set to off in the video.

Edit: mine is a Volvo s40 2004 1.9t

Post by **abscate** » 04 Aug 2019, 03:29

Probably either normal AC hiss from rundown, or, if gas is released, a hole in the evaporator. Your AC will stop working pretty soon if the evap gets holed.

Post by **alschnertz** » 05 Aug 2019, 14:26

My '01 makes noises under the dash on occasion. Definitely coming from the heater blower motor area and does it when stepping on the brake. I don't believe the sound is vacuum related as it will make the radio static(y) at the same time. I suspect it's a wonky ECC in my case.

I can't think of any toxic gasses other than R134A which will dissipate rather quickly, like within minutes, as it empties your A/C system.
The only other thing would be coolant from a leaking heater core which may be somewhat irritating.

Post by **abscate** » 14 Aug 2019, 06:59

The late P80 and P2 HVAC systems have an after-run feature will which leave the blower on low speed - if you have some oil reside in the motor it might t be picking that up and pumping it into the cabin when the engine is off and the car still.

Refrigerant doesn't really sting your eyes - its an inert gas. Also an AC leak ends in seconds or minutes at most.