Hissing under Dash



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Thread: Hissing under Dash

  1. #1
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    Hissing under Dash

    96 Town and Country with Rear AC. For the past few months ive had a strange hissing noise coming from what sounds like behind the glove box. It sounds like steam traveling in a tube and is usually followed by warmer air from the AC. I replaced a leaky AC line and recharged the system and didnt hear the noise for several weeks now its coming back.

    My question is this. Is it something to do with low pressure thats making the R134a make the hissing noise inside the system, which will tell me that i still have a leak. Or is this something else?


    Sometimes i hear the same strange noise from the Rear system as well, at the air exchanger back there.
    1996 Chrysler Town and Country LXi 3.8l 115,000
    1997 Buick Regal 3.8l 99,588 (totalled )
    1985 Buick riviera 5.0l 80,000
    1972 Lincoln Mark IV 460ci 114,000
    1989 Lincoln Town Car Signature 5.0 85,000
    2000 Buick LeSabre 3.8l 94,000

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  3. #2
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    Question

    Quote Originally Posted by jase386 View Post
    96 Town and Country with Rear AC. For the past few months ive had a strange hissing noise coming from what sounds like behind the glove box. It sounds like steam traveling in a tube and is usually followed by warmer air from the AC. I replaced a leaky AC line and recharged the system and didnt hear the noise for several weeks now its coming back.

    My question is this. Is it something to do with low pressure thats making the R134a make the hissing noise inside the system, which will tell me that i still have a leak. Or is this something else?


    Sometimes i hear the same strange noise from the Rear system as well, at the air exchanger back there.
    This is your A/C system audibly telling you it's low on freon. Yes, you most likely have a leak. There is a dye that can be added to the system next time you add more freon. Did you replace the seals when you replaced the line ?
    1990 Plymouth Grand Voyager LE 3.3L LWB-- 222,222 miles and counting ......
    Still Going Strong


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    From my experience, if you can actually "hear" a freon leak, you won't hear it for very long.

    I was going to say that it could be a vacuum leak, which could also have the result of you feeling warmer air by preventing or causing the vents not to operate properly, also, not positive with the Caravan, but some heater values utilize vacuum pressure to prevent the heater valve from opening....but apparently you are losing freon since you did a recharge and it went away then returned.....

    Hope it turns out to be a relatively easy fix.
    1999 Grand Caravan SE
    2006 Caravan SXT

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    I can hear a similar noise from the rear a/c of my '97 T&C. Right when I turn it on for a few seconds. It's always done it and worked fine, I figured it was just the expansion valve opening up or something. 12 years on the original a/c and still ice cold, thats what I'm talking about.
    2001 Infiniti i30 3.0 DOHC V6: VQ30DE 177,000 miles; 1999 Nissan Altima GLE KA24 168,000 Miles
    1997 Dodge Ram 1500 SLT Laramie 5.9 46RE, 182,000 Miles
    Prev. 97 T&C LXi 184k 3.8, 94 T&C 3.8 156k Miles, 93 GV LE 3.3 123k

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    the line that was replaced was the one that drops straight down behind the radiator and curves down to the condensor. i was standing there when he pulled it off and there was no extra seals other than what was made onto the ends of the hose. that hose was leaking where the metal clamps to the hose.

    Sideburns i think the noise youre hearing is the little electric motor that tells the door which way to blow the air in the rear.

    mine sounds like steam thru a straw. or similar to blowing up a balloon, just not as loud.

    i guess ill fill her up again *sigh* and see how long it takes this time, then drag out a black light.

    side note, my AC isnt original, it was replaced under factory warrantly years ago, but this is the first problem its had since then
    1996 Chrysler Town and Country LXi 3.8l 115,000
    1997 Buick Regal 3.8l 99,588 (totalled )
    1985 Buick riviera 5.0l 80,000
    1972 Lincoln Mark IV 460ci 114,000
    1989 Lincoln Town Car Signature 5.0 85,000
    2000 Buick LeSabre 3.8l 94,000

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    Quote Originally Posted by jase386 View Post
    the line that was replaced was the one that drops straight down behind the radiator and curves down to the condensor. i was standing there when he pulled it off and there was no extra seals other than what was made onto the ends of the hose. that hose was leaking where the metal clamps to the hose.

    Sideburns i think the noise youre hearing is the little electric motor that tells the door which way to blow the air in the rear.

    mine sounds like steam thru a straw. or similar to blowing up a balloon, just not as loud.

    i guess ill fill her up again *sigh* and see how long it takes this time, then drag out a black light.

    side note, my AC isnt original, it was replaced under factory warrantly years ago, but this is the first problem its had since then

    No it's when I turn the a/c on.(hit the snow flake button) Once the compressor circulates 134a it goes psssssssssssshhh then its done. I can "hear" the pressure build. Kind of like when I turn my Ram off I can hear the pressure releasing from the condensor up front with a similar psssss noise.
    2001 Infiniti i30 3.0 DOHC V6: VQ30DE 177,000 miles; 1999 Nissan Altima GLE KA24 168,000 Miles
    1997 Dodge Ram 1500 SLT Laramie 5.9 46RE, 182,000 Miles
    Prev. 97 T&C LXi 184k 3.8, 94 T&C 3.8 156k Miles, 93 GV LE 3.3 123k

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    I do heating and cooling for a living and I can tell you this much, chances are you are low again for whatever reason, put some gauges on it before you speculate yourself to death, if it is any lower than where you had it at you know what to do, otherwise we'll go from there, but I doubt it.
    99 plymouth grand voyager se, 3.3 engine, 185 000 mi. recently replaced engine, repaired strut towers, and other odd ball repairs and now just finished rebuilding the tranny, should be good for a while.

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    Quote Originally Posted by sideburns2009 View Post
    No it's when I turn the a/c on.(hit the snow flake button) Once the compressor circulates 134a it goes psssssssssssshhh then its done. I can "hear" the pressure build. Kind of like when I turn my Ram off I can hear the pressure releasing from the condensor up front with a similar psssss noise.
    Mine did the same till I had them find and repair a small leak because it was low on charge, pulled a vacuum and refilled, no more hissing now.

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    Quote Originally Posted by Stretch View Post
    Mine did the same till I had them find and repair a small leak because it was low on charge, pulled a vacuum and refilled, no more hissing now.
    Well it's done it as long as I can remember. Years....and the a/c works just as good today as it did years ago. hmm...
    2001 Infiniti i30 3.0 DOHC V6: VQ30DE 177,000 miles; 1999 Nissan Altima GLE KA24 168,000 Miles
    1997 Dodge Ram 1500 SLT Laramie 5.9 46RE, 182,000 Miles
    Prev. 97 T&C LXi 184k 3.8, 94 T&C 3.8 156k Miles, 93 GV LE 3.3 123k

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    I believe the reason that you hear hissing is that when you turn your system off, your high side is still somewhat pressurized. As the high pressure dissipates through the expansion valve into a low-charge low side, there's your hiss. When I hear this, I know my charge is low, and I simply add a $6 can of R-134a, and the hissing is gone for another year or two.

    1988 Chrysler LeBaron Convertible, 2.2L Turbo (original owner)
    1996 Town & Country LXi Van, 3.8L
    1989 Beretta GT 2.8L V6 (original owner)
    2009 Honda Accord EX 2.4L I4 (original owner)

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