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why won't A/Cwork after refrigerant top-off?

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Old 12-12-11, 07:26 AM   #1
ancdmd
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Default why won't A/C work after refrigerant top-off?

I've had recurrent air conditioning problems for a couple years on my '02 UL. Sporadically the A/C blows warm air for about ten minutes before suddenly blowing cold. It used to have this problem more often after the car had been sitting overnight. Also has a tiny leak in the evaporator under the dash, which is insanely expensive to fix, so instead I just top off the refrigerant every ten months or so. Multiple mechanics and dealers cant find the cause of the delayed cooling. I found that a likely culprit was the high-pressure switch, which I had replaced last year. The issue seemed resolved for the most part this past year, but then it started up again not too long ago.

Cut to Friday, I had the refrigerant topped off, it was .75lb low, and now the A/C only blows cold half the time. Friday evening it started blowing hot, continuing into all day Saturday. Sunday it blew cold all day, then hot again in the evening and this Monday morning.

There's no correlation to engine temp, outside temp, etc. Sometimes it works, sometimes it doesn't. It won't start blowing cold air WHILE I'm driving either. After I start the car its either blowing cold or not, and it won't have a chance of blowing cold again til I shut the car off and restart it.

WTF!?!?!?!
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Last edited by ancdmd; 12-13-11 at 07:08 AM.. Reason: spelling
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Old 12-12-11, 01:24 PM   #2
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Too much refrigerant fill can make the compressor malfunction also but you likely know that.
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Old 12-12-11, 04:06 PM   #3
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Should I maybe try to release some of the refrigerant and see if that works?
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Old 12-12-11, 07:16 PM   #4
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A sticking expansion valve will allow the system to function one moment and fail the next.
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Old 12-13-11, 07:09 AM   #5
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where is the expansion valve?
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Old 12-13-11, 08:42 AM   #6
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i think its close to the fire wall if i"m not mistakened
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Old 12-13-11, 06:30 PM   #7
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The expansion valve meters the flow of refrigerant into the evaporator coil (the coil that gets cold). I don't know where it is in the LS. It's sometimes under the hood near the firewall but more likely it's underneath the dash just before the evaporator coil. A qualified HVAC technician can put gauges on your system and determine what your problem is by looking at the high and low pressure gauges while your system runs. That is really the easiest way to get to the bottom of this.
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Old 12-17-11, 12:14 PM   #8
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I was able to have my mechanic check out the car while the A/C was blowing warm. He and another tech figured out that the compressor is bad. They recalled the same situation on another LS quite some time ago, took them a long time to figure it out. Apparently there's some metal plates or something in the compressor that are malfunctioning. Removing about a half pound of refrigerant caused the compressor to kick on and it's working ok for now, but a permanent fix will require replacing the compressor.
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