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I am a part time auto mechanic, and for the life of me cannot figure out this problem. No matter how many times I fix it, two weeks later it comes back. I cannot fix the air conditioner. I have installed a new compressor, new orfice tube, new dryer, vacuumed the system and replace the freon. It works for two weeks and then starts blowing warm air. Then, I go back and check the freon pressure and it is good. Next, I vacuum and replace the freon again, and it works for two weeks then starts blowing warm air. After checking the freon pressure again, it is still fine. Please help! Thank you.

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Sounds like you have a slow leak. – Nick Sep 7 '13 at 14:46
@Nick Even though his freon pressure remains normal? – Seminecis Sep 7 '13 at 17:25
Is it possible that the A/C is ok and the issue is the damper door mixing hot air. Check the a/c lines under the hood to see if they feel cold. – mikes Sep 7 '13 at 19:39
up vote 4 down vote accepted

You have a leak in the system. You can't use the pressure to tell if you have the correct amount of Freon. If you were using a recovery machine that weighed the amount of recovered Freon you would see that you are loosing Freon. Not only is Freon leaking out, non condensable gas (ie air) is getting in. This is causing your pressures to look right even though you are low on Freon.

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