what's that hissing sound?

[CL Wong]

It was about 15 degrees this afternoon in NJ when I
left work.  Got into my car and the engine cranked
sloooowly.  Luckily it started within a few turns this
time.

Steering was stiff and the car simply felt like it
didn't like the cold.  After I started driving I began
noticing a light hissing sound coming from the
dashboard area.  

About 2-3 minutes later, the heater started blowing
and I couldn't hear the hissing anymore.

I'm guessing that the hissing sound is related to the
climate control somehow and that I probably have a
leak, but where?


thanks in advance!

Chi


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