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.
Best Answer
Most residential AC system thermostats only turn on based on temperature. And most residential AC systems only dehumidify when then AC is cooling. Therefore, it's very possible that the AC is cooling the house faster than it can dehumidify. Try turning the thermostat down a couple of degrees.