A/C Interior Hissing Noise

Discussion in 'General Motoring' started by Scott Ehardt, May 5, 2004.

  1. Scott Ehardt

    Scott Ehardt Guest

    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.

    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.

    Scott Ehardt, May 5, 2004
  2. Scott Ehardt

    Gene Poon Guest


    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.
    Gene Poon, May 5, 2004
  3. Scott Ehardt

    Scott Ehardt Guest

    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.
    Scott Ehardt, May 6, 2004
  4. Scott Ehardt

    Joe Guest

    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.
    Joe, May 7, 2004
  5. 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 ?
    David Russell, May 10, 2004
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