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Starting last summer, my car started making a strange hissing noise when the a/c was on. It started out as an intermittent thing; sounding something like a a turbo spooling up and ending with a sound like the valve on an airhose being slowly closed. It didn't seem to effect the temperature of the a/c. Soon, however, it became a continuous hiss; vaguely metallic but largely like an airflow type sound. It only occurs when the a/c compressor is on. The strange thing is that the compressor seems to run year-round; even when it was far below zero last winter I would hear the clutch engage and the hiss would start. The book symbol has been going on and off intermittently; and now the a/c doesn't blow cold at all anymore. The RAVE cd said that a low charge in the system could cause a hiss; so today I had the a/c recharged. I just drove the car back from the mechanic and its still not blowing cold at all and the hiss is still there. Thoughts? Its starting to get hot and I can't drive around in an a/c-less car all summer! I hope its not the compressor or some kind of a leak somewhere.
 

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Just out of curiosity have you tried the heater - does it still blow hot air as it should? Does the temperature adjust up and down correctly?
I ask because I have just had my system read for the ´book´ symbol and it turned out to be relay RL7 at the front of the under-bonnet fusebox. The relay was dead and as soon as I swapped it with another (the 3rd one back RL5) I had heat that I had never had and my a/c suddenly worked properly. I am under the impression that if one of the relays is dead or dying the appropriate blower won´t function correctly and so the a/c is unable to suck through the condensor properly.
It´s just a thought . . . and I stand corrected if appropriate.
 

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This would be the sound of the air con gas flowing past the expansion valve. Happens when the expansion valve gets partially blocked. Replacement is the only option, if indeed you call that an option.
 

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Before having the A/C system regassed - it's a good idea to check for leaks - normally done by adding a special "tracing additive" which can be seen using ultraviolet light... But you can also check it by "pressurizing" the system with nitrogen - had it done on mine last week - the A/C system suddenly stopped working - but was solved with at new condensor - took the garage a just over an hour took take the old one out - moving fans and putting the new one in - adding gas etc. Actually not bad I think.....

just my penny....
 

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My 97 RR 4.6 does the same hissing sound when the A/C is on. Has been doing it for at least a year. Still blows cold though.
 

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1995-2002 Range Rover P38A
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I just went through this, I had the hiss sound for a while 3 months then no a/c at all. I went down to local parts store and purchased two cans of freon one of those cans had dye in it. I pumped in the dye then looked for the leak with the ultraviolet lite that came with the package. Nothing, I then went out at night, low and behold there it was, all my dye leaking out of a bolt on the back of the A/C compressor! It looked like a river flowing :lol: :lol: So I tightened up the bolt recharged the A/C and presto great cold A/C... It's been about three months now and still cold!!

Good Luck
 

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Scotty said:
I just went through this, I had the hiss sound for a while 3 months then no a/c at all. I went down to local parts store and purchased two cans of freon one of those cans had dye in it. I pumped in the dye then looked for the leak with the ultraviolet lite that came with the package. Nothing, I then went out at night, low and behold there it was, all my dye leaking out of a bolt on the back of the A/C compressor! It looked like a river flowing :lol: :lol: So I tightened up the bolt recharged the A/C and presto great cold A/C... It's been about three months now and still cold!!

Good Luck
Hi, Scotty,
Mind telling me where did u purchase the freon can with die.

thnks

kapila
 

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You can buy it at just about any auto parts store here in the U.S. - Napa, Advance, Auto Zone, etc.

But IIRC you are not in the U.S.....please put your location in your profile! It really does help.
 

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As Chris said NAPA
 
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