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Why is my AC hardly cooling and not dehumidifying?

Josh C
last month
last modified: last month

Our AC is having some problems. The difference in temperature from return to supply is only about 12-14 degrees, and the air coming out does not feel dehumidified. In fact, while we have our AC on, the hygrometer actually will show humidity increase slightly the longer it's left on. The temperature in the house also hardly drops, even when left on for an hour.

Example: on an 80 degree day with 50% humidity outside, trying to lower the indoor temp from 74 to 72 may take almost an hour, and during that time, the humidity in our house may increase from 67% to 70%.


  • Our house is about 1600 sq. ft, built in 1958
  • Furnace is located in the garage
  • Three return ducts located in the attic
  • The AC is a 2 ton unit, both it and the furnace were installed around 2016
  • Crawlspace has a dehumidifier running, with a moisture barrier laid out (no vapor barrier on block walls though)
  • Air filter was replaced last week
  • Condensate trap was fine and the condenser unit was cleaned last week
  • Also aware that our attic insulation is low at around R16 and we need to at least double that
  • We have a fireplace, and I'm now realizing I should check if the flue is closed

We are already aware of an uninsulated 8' of return duct in our attic (attic is a little too hot, but that's being addressed), and also aware that our blower fan needs cleaned as it's a bit dusty. However I am not convinced that either of these are the root of our problems.

We're going to have a second opinion/deeper inspection and diagnosis from another company since I don't believe the first did enough to diagnose other than pointing out the return duct is not insulated and speculated that all need replaced without any testing.

I'm suspecting the following as potential causes, would really appreciate some input on what might be wrong here:

  • Low on refrigerant / refrigerant leak
  • Air leaks in supply / return ducts
  • Something wrong with the evaporator coils (pic below, unsure if that looks right)
  • House is letting in outside air from somewhere when the AC is on for some reason (idk if that's possible?)

Thanks all, please let me know if I can provide any other information to help diagnose, this has been driving me crazy and I'm dead set on getting this fixed.

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