A/C Interior Hissing Noise

The short: I just had my A/C system evacuated and recharged. Now there is
a hissing noise on the inside that was not there before, but it cools well.
Why?

The long:
1998 T&C Van
A couple weeks ago I started my van in a parking lot after having it off
for about an hour. I soon noticed a hissing noise from the engine audible
over the radio, so I pulled over about 20 feet from where I started. Once
stopped, there was some type of smoke/steam coming out from under the hood
with a slight odor. By the time I had the hood open (engine off), the
hissing had become much quieter. I eventually traced the hissing to the
compressor area and decided it was the compressor due to the presence of
some light oil nearby. After 10 minutes it was still hissing so I decided
it was just going to leak out and I drove off (with the A/C off, and I kept
it off until it was fixed).
Recently I took the van to the shop where they replaced the "air
conditioning high pressure hose seal" and evacuated and recharged the
system. It worked well for about a day, and then today I noticed a hissing
sound on the inside this time. At the time I thought it wasn't cooling, but
I have since decided that I just didn't leave it on long enough, since
turning the A/C off stopped the hissing noise and I thought something might
be wrong. I took it back to the shop and they looked at it and said
everything was ok.
The A/C is still making the hissing noise intermittently, but not as
loudly. Cooling is excellent (possibly better than before all this
happened). The front evaporator hisses separately from the back one. I
recall hearing this noise in other cars, but not in mine before or in my
dad's '02 T&C. So as long as the A/C seems to be cooling properly, is this
noise cause for concern? I don't really care if it makes the noise, just
wanted to make sure nothing is wrong.

Thanks!
Scott

 

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As the liquid refrigerant evaporates in the cooling coil under the dash
(appropriately called the "evaporator"), thus absorbing heat, there will
be a slight hissing sound emitted. Perhaps previously your air
conditioner was low on refrigerant, so less liquid refrigerant and more
gaseous was present, reducing the hissing sound. You already say the
A/C cools better than before, which supports this hypothesis.

 

I agree that the evaporating refrigerant would produce a slight, constant
hissing sound. However, what I have is a somewhat loud hissing sound that
comes and goes frequently while driving. It seems to me this might mean the
system is actually low on refrigerant so sometimes air is rushing through
the evaporator nozzle (the hissing sound) and at other times there is liquid
coming through like it is supposed to which does not make an audible sound.
If you compare this situation to the sound a faucet makes when you have air
in your pipes (say, after turning the water off for a winter vacation) it is
similar. There is little to no sound when water is coming out but very loud
sounds when air is rushing much more quickly through the same size opening.

 

I didn't see the original post, but if that is what you think, then I
suggest trying to correlate the sound you hear to the on/off cycling of your
a/c compressor. That would very easy to do, but I will leave how you do it
up to you. Then at least you'll know why it comes and goes.

 

I had the same problem with my 1998 Grand Voyager.
Took it to the local dealer who had worked on the "gates" behind the dash
area near the radio prior.
After 4 hours they came back and said they could not find anything but they
re gassed it and said there would be no charge for time incurred ?
Strange but true. I asked twice but could not get a straight answer. But i
think it could be a joint leak behind the dash area.
Maybe disturbed by them ?