Posted by
Member since Dec 2003
315 posts

Oversized evap coil - what to do?

Had inside and outside unit installed 10 years ago by a guy who worked for a big A/c company. He was a friend and did it on the side to cut me a break. Anyway, over the years I’ve noticed some mold on the diffusers and it cools pretty quickly, so it’s not removing enough humidity in the house. Finally got around to looking at model numbers and as suspected, I’m running a 2 ton condenser and 4 ton evaporator coil inside. 2000 sq ft house. What are my options besides replacing the coil with the right capacity?

Member since Oct 2014
302 posts

re: Oversized evap coil - what to do?
You can slow the blower speed down if its a 4 speed motor to medium high instead of high in the evaporator (probably in attic on the unit circuit board) and this will cause unit to run longer as it doesn't cool the air as fast. It should be as easy as swapping the fan lead for cool from high terminal to next lower speed. I did this in my house and I have noticed a difference in condensation on ceiling grilles. My units are probably a little oversized, but I think you can under charge the unit with freon and do the same thing.

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Member since Jan 2022
126 posts

re: Oversized evap coil - what to do?
A 2 ton condenser for a 2000 sq ft house seems undersized.

Do the units keep up in the summer?

Member since Nov 2022
5 posts

re: Oversized evap coil - what to do?
You have an undersized condenser

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TD SponsorTD Fan
Member since 2001
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Mississippi St. Fan
Member since May 2012
8138 posts

re: Oversized evap coil - what to do?
Are you sure it's a 2 ton condenser? I'm having a hard time believing it really is a 2 ton if you got through this summer. That or either it just stayed on 24/7

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Baton Rouge
Member since Oct 2010
244 posts

re: Oversized evap coil - what to do?
Standard rule 1 Ton every 400 square feet

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Baton Rouge
Member since Apr 2019
5119 posts

re: Oversized evap coil - what to do?
Does the condensing unit model number have a “24” in it (indicating 2 ton unit) as opposed to 30, 36, 40, or 48 somewhere in the model number?

That you state the system cools down the house quickly and is not removing enough humidity (have you measured relative humidity in the house?) in itself suggest that unit is not undersized. Just double checking to make sure that you’ve correctly concluded that condensing unit is 2 tons as that just doesn’t seem like a mistake a tech would make?

It’s common for a evap coil to be rated at 1/2 ton larger than the condensing unit but not 2 tons.

Supply vents can sweat for many reasons, here is good article discussing potential causes - do any of these apply in your case?

Why Do Air Conditioning Vents Sweat

deathinthedelta provides a good suggestion that the first thing to try if the unit is short cycling, and thus resulting in high humidity, is to slow the air handler or furnace blower speed from a “high” speed setting to a “medium high” or “medium” speed setting on the cooling tap on the air handler/furnace control board, but if the blower speed is reduced too much, for example, setting the speed tap on “low”, it can freeze the evaporator coil.

This post was edited on 9/23 at 6:35 pm

Nawlens Gator
Florida Fan
Member since Sep 2005
5680 posts

re: Oversized evap coil - what to do?
I installed a 4 ton outside unit (compressors, condenser, fan) and a 5 ton indoor unit (evap coil, blower) for a 2200 ft2 house 25 yrs ago (knock on wood). The owners manual shows how to swap connectors on the evaporator to achieve different blower speeds.

Outside unit has 2 compressors, a 2.2 ton and a 1.5 ton where either compressor runs alone or both run simultaneously (depending on outside temperature and indoor temperature difference from set point). In the summer, the 2.2 ton compressor starts first and it is usually sufficient to keep the house cool without the second compressor. Seldom are both compressors needed. In cooler months the 1.5 ton compressor starts first and is usually sufficient to keep the house cool. Indoor setpoint is either 74 or 75 deg.

Running smaller compressors for longer time periods helps reduce humidity which feels cooler.
This post was edited on 9/23 at 3:25 pm

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