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Question DetailsAsked on 7/21/2017

As the house cools down, does the condensation on the indoor a coil decrease?

I just had indoor and outdoor unit replaced today. Old had lots of condensation but as the freon leaked out, there would be no more.
I'm just a bit worried because house is cooling off great, but there's little condensation on the inside unit. Very old air coming out of vents though. Will the new unit produce less since there are no leaks?

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1 Answer


I presume you meant very cold, not old, air coming out of the vents. If it is around, typically, about 15-25 degrees cooler than the incoming air to the coil (measured fairly close to the coil on the output side, not way down the duct), then probably doing good.

The old unit may have been getting overly cold - as the charge in the unit drops enough to affect the return pressure, eventually it drops low enough that the coil is essentially dropping from the compressed high pressure (maybe 150-300 psi, generally speaking, without getting into specifics on a particular unit, for R-410a) to near zero on the output side, rather than from the 150-300 psi high side range (depending on ambient temperature) to maybe 50-100 psi on the "suction" side as it should be. That greater pressure drop in the coil causes excessive cooling in the coil, causing freezeup. Of course, if the coil was dirty (likely) the airflow through it would have been reduced, so there would usually be more condensation on the coil in that case too, because the airflow through it would have been reduced so the cold coil could remove more water (something which is intentionally done in dehumidification A/C systems) from the air, rather than just removing some and letting the rest pass through to the conditioned air passages.

If the air coming out is good temp (commonly about a bit under 20 degrees cooler than incoming) AND the evaporator coil is not freezing up significantly (though some external pipes may have frost buildup on them, especially those outside the plenum/ducting on the output side) all sounds good. Note that the 15-25 normal reduction in air temp is between the incoming AT THE COIL and the outgoing AT THE COIL.

In a unit starting up after a long shutdown (say away at work), this might for instance be say for illustrations sake, 20 degrees cooler than the hot house - let's say you are in toasty West Texas at a mild 100 degrees outside and maybe 90 degrees in the house after sitting through the day - so initially (after a couple minutes operation) the output air temp might be about 70. However, as the unit cools the house down, normally the air handler/blower will be mostly recirculting indoor air with little outside air being added by infiltration or as makeup air - so as the house cools down, it would still track roughly 20 degrees below the HOUSEHOLD temp - so by the time the house got down to 70, the register air might be near 50 degrees (and at that point you would likely be icing up the evaporator, which should normally not run below about 55-60.) Of course, normally the thermostat would turn the unit off before then - but that is how say a well-operating motel A/C left on full can get the room down, even on a pretty hot day, to the point the glass is condensing moisture on the outside and the room is around 60 or less - granted after a lot of wasted energy from many hours of the A/C running.

Where it is in the cycle also makes a difference - initially when the unit kicks on after a long sit, it is generally going to be processing warmer air with more moisture in it, so it will condense more moisture and more water will come out the drain tube. As it circulates the air through the house, reducing the humidity, it will condense less, even though the coil and the air temp as cooler than initially.

And of course, ambient/outdoor humidity makes a big difference too - on a hot muggy or rainy day it may stream a pretty consistent condensation haze, on dry days (even if hot) there may be little or no visible condensation or drain tube dripping.

Answered 3 years ago by LCD

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