Hissing from defrost even though ac is off.

[Slawski]

Happened for the first time today. The hissing becomes louder the higher the rpms go. Only thing I think it could be is some water got in the vents when it was heavily snowing two days ago.
Any suggestions?

Sponsored

 

[Hootbro]

Hissing is not uncommon in defrost mode. Even in defrost mode and with the A/C button showing off, most vehicle A/C systems will still cycle the A/C compressor in defrost mode regardless to remove moisture from the incoming air.

This in turn cause the expansion valve to operate and allow incoming Freon to pass through the evaporator core inside the cabin and that can cause a hissing sound due to rapid gas/liquid conversion. The colder it is outside when turning on the vehicle and selecting defrost, the more it can hiss but should eventually go away.

If it continues to hiss, it also may be low on Freon and should be checked. These take the new R-1234yf refrigerant so it will need a specialized shop that deals with it