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Before I load you all up with my latest problem I have to say thanks in advance. You guys have helped me A LOT and my car would not be the same without you guys! Okay now that I'm done kissing butt heres my problem :O
When I have my AC on more then 20 sec or so I get a loud hum coming from under the hood. I looked to investigate and I'ts coming from this valve looking thing. I'ts right by the box where the fan is. It is cradled by a black metal hook looking thing following a metal line under the fender. I don't know what to call it? Anyway anyone had the same problem with their ac? I am stumped


Thanks for the help

P.S. It is NOT vibrating against the hook or fender.

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Hot66ss

66 ss
67 malibu
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Discussion Starter #3
I dont know about the vacume thing but yes the air works, just does not get quite as cold I would like.

Thanks

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Hot66ss

66 ss
67 malibu
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Well haven't seen 66 a/c in awhile so i cant really picture the explanation. When low on freon the TXV could "Hissss" but don't think you would here it with the hood shut. Maybe the bearing is going out on the blower motor, that would hum.
 

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Is the piece called the muffler?May it needs replacing.

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John 67SS
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I don't know what its called.i can feel the thing vibrate when its making the noise so i know its NOT the blower. the compressor is new.


Thanks

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Hot66ss

66 ss
67 malibu
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Discussion Starter #7
I don't know what its called.i can feel the thing vibrate when its making the noise so i know its NOT the blower. the compressor is new.


Thanks

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Hot66ss

66 ss
67 malibu
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Discussion Starter #8
I don't know what its called.i can feel the thing vibrate when its making the noise so i know its NOT the blower. the compressor is new.


Thanks

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Hot66ss

66 ss
67 malibu
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Taking a shot here... this sounds like the expansion valve. An aluminum piston in an aluminum bore if it's like the one we got curious about on a 67 and cut open. If the air wasn't used for a long time they tend to seize up and the expanding gas 'buzzes' as it tries to do it's job. Good news is it usually gets better with more use, bad news could be that when the compressor was changed the oil wasn't added to the system.

fwiw.
 

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From your description, it sounds like the POA valve is starting to malfunction. Does it maybe get super cold on one side of this component and not so cold on the other side? I don't remember what POA stands for, but it controls freon flow in earlier GM ac systems. The POA is a different valve from the expansion valve. The expansion valve is the one that the high pressure line (small) goes to just before it goes into the ac box. It allows the hot, compressed, liquid freon to expand very rapidly into a gas. This rapid expansion is what causes the ac unit (evaporator) to get very cold. The POA valve is on the other end of the ac box, which is the suction side (big hose). The POA valve controls the flow or suction rate of freon out of the evaporator going to the suction side of the compressor. Anyway, if this valve is starting to malfunction, maybe there is some sort of buzzing or vibration going on inside which results as a hum. They are kind of expensive to replace. But when these systems are in proper working order, they do work good. They are worth the expense to maintain, in my opinion.

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Ok I think Al has this one. the previous owner of the car (A MUD SUCKER) pawned the car and was sitting and not moved for over 3 months. when the air is going this thing gets real cold like a think it should but I get that annoying hum. I think I'll try using the air more and see if it clears up. How long of running the air does it usuly take for this valve deal to shut up?


THANKS FOR THE HELP SOUNDS LIKE YOU GUYS JUST $AVED ME SOME $$$.

P.S I don’t think that oil thing as Al mentioned is the prob because the replacement was done by a respectable pro=)


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Hot66ss

66 ss
67 malibu
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Discussion Starter #12
Ok I think Al has this one. the previous owner of the car (A MUD SUCKER) pawned the car and was sitting and not moved for over 3 months. when the air is going this thing gets real cold like a think it should but I get that annoying hum. I think I'll try using the air more and see if it clears up. How long of running the air does it usuly take for this valve deal to shut up?


THANKS FOR THE HELP SOUNDS LIKE YOU GUYS JUST $AVED ME SOME $$$.

P.S I don’t think that oil thing as Al mentioned is the prob because the replacement was done by a respectable pro=)


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Hot66ss

66 ss
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Just to clarify, Al was actually referring to the POA valve not the expansion valve. Thanks DZ.
 
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