Reader Question: I have a 2001 Mazda 626. When I start my car, it makes a hissing sound and in my trunk on the right side, there is water inside the side pocket.
Also, the air conditioning vents inside my car have been spewing out black fuzzy pieces of something. What is this?
Hi there Diane,
The water in the trunk is probably due to a leaking trunk weather strip or the trunk lid itself needs to be adjusted by a body shop. A body shop is probably the best place to have this leak looked at.
The hissing noise, if you hear this noise more so on the passenger side of the vehicle like around the glove box area and only hear it when the AC is on, I would have your mechanic check the AC expansion valve and the evaporator core.
The black stuff you are getting out of the vents is probably from mold inside the AC system OR it could be pieces or the rubber insulation around the AC blower motor, which is also on the passenger side glove box area inside the dash.
You could be hearing the Freon gas flowing through the expansion valve (which it is supposed to do) but you might have a slight restriction in the valve causing the hissing noise. If the hissing noise is not present with the AC OFF, then I am probably correct in thinking there is a problem with the AC expansion valve. You can see pictures of these parts under the HVAC category.
I had a customer with a Toyota truck and a periodic hissing noise with the AC on, and we determined his expansion valve was at fault, but the AC worked fine and he continued to live with the noise for years.
If the hissing noise is under the hood, open the hood with the engine running and look for a broken rubber hose or hose connection that could be causing a vacuum leak.