air conditioning not working right

imhotashellJuly 12, 2012

Our air conditioning unit has been working great till this year. Had it serviced 2 weeks ago. Needed a new coil as the older one had a leak. Unit is only 6 years old. Today outside temp is 95. Unit in house set for 72. Its been blowing but staying at 74 all day and will not go down to 72. Vent temp is 67. Called 2 days to complain. Company said if its icing up there is a problem. But its not icing up. Outside temp now is 72. but the air cond is still running full out and house will not go below 73. What cold be wrong ? I pulled the filter out to give max air flow. Im wondering if the coil they installed is too small ??? although they said it was the right size. Full pressure will full freon (or whatever its called now). There is no way it should be running and not go down to the temperature in the house that it is outside. Any ideas ???

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Delta T is only 7 (74-67), some thing is not right. Go outside hand touch the 2 copper pipes, the large insulated one should be ice cold and wet, the small one should be just a little warm, if not, there is a problem.

    Bookmark   July 12, 2012 at 11:43PM
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I did as you said. The insulated one is cool/cold.... not ice cold.. but its wet. The other one is just warm. What do you mean delta T ??? Yes... inside 74 and the vent is 67... so why is it not cooling off the inside to cooler than 74 ??? Its 11pm now. I reset it at 73 and it now just shut off. The installer ( old drunk guy it looks like ) said it is working fine as long as it is not icing up, which it is not. He said its fully charged and not leaking.

    Bookmark   July 13, 2012 at 1:06AM
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ok... read up on Delta T. Can you explain to me what I should be complaining about to my installer ? There is no way the AC should be on for hours staying at a 74 temp and not go down if the vent air is 67.

    Bookmark   July 13, 2012 at 1:12AM
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Delta T should be at least 15, I prefer 16 or 17. in your case, the room temp is 74, then the input vent air should be around 58 or 59 (not 67). SO the vent air is not cold enough, that is your problem. Call the installer back, tell him you want delta T at least 15 (in my city, 15 is the minimum to past city or real estate agency inspection). This problem can be caused by many reasons (lack of freon, dirty filter, dirty coil, leak air duct, frozen coil, unmatched coil, blocked pipe, etc.....) ask the installer to figure it out and fix it. Insist on 15 Delta T.

    Bookmark   July 13, 2012 at 10:35AM
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The delta T should be about 18 degrees F for a good working unit. Is your airhandler in the attic? If so, there is a possibility the return (intake)ductwork to the air handler was damaged during coil replacement. It would be sucking hot attic air across the coil.

    Bookmark   July 13, 2012 at 10:36AM
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busboy is right, make sure they re-seal everything to prevent air leaking after the install. check the plenum and all the duct to make sure.

    Bookmark   July 13, 2012 at 10:46AM
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67 supply air is too high. Should be in high 50s-low 60s at the most. This suggests a bad refrigerant charge or leaks in ductwork system. Filters have been changed?

This should be tech's starting point as far as solving your problem.

BTW, coil is a matching coil and correctly sized?-probably not.


    Bookmark   July 13, 2012 at 11:36AM
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