Two months ago, I posted about our upstairs a/c not cooling all of a sudden. I ended up replacing the capacitor for the blower fan and the contactor, which did the trick. AC cools!!! However since then, there has been increased humidity upstairs (>60%), and I just can't figure out why. We keep the temperature between 75-78, and live in NC. It seems to be related to this unit, as the downstairs air at the same temperature, has lower humidity (<60%).
As I understand, humidity comes out of the air as it is cooled across the coils, in the form of condensation. It is captured in the pan under the evap coils. There is a drain to evacuate water to an overflow pan from the pan beneath the coils when it gets to a certain level.
Please tell me what else I am missing from my understanding of how air is dehumidified in a central ac unit (without a separate dehumidifier). I don't know if there is a fan that "evaporates" off the condensation like there is with a refrigerator or freezer.
This is what I've inspected/done:
- Inspected drain pan, which was bone dry.
- Accessed the evap coil, and found 1/2 inch of water which I drained. No blockage to the overflow pan. There is some rust on coils and at the bottom of the pan, but I didn't see any pitting or obvious leaks.
- Fins over the eval coils were pretty clean - no dust.
- Cleaned the fins on the coils in the outside unit which were dusty
There must be something fundamental I don't understand, because if unit is cooling to the correct temperature, it seems that we don't have a cooling or a handling issue. But why would humidity be an issue now, if it wasn't before, and particularly, only on this one unit.