AC Maintenance: Evaporator Coil

Video Transcript

Evaporator Coil Maintenance

Dean:        We’re gonna cover evaporator coil next. A coil’s a coil’s a coil, right? So the coil’s under the house, it grabs heat or it gets rid of heat. So it needs to be cleaned just like an outdoor coil.

George:     Right, if it’s got a bunch of dust or animal hair or whatever, the airflow’s gonna be affected flowing through that coil, just like it is on the outdoor coil.

Dean:        Make sure it’s clean, fins shouldn’t ever be crooked or bent, unless somebody’s been in there and messed ’em up. Next thing evaporators, make sure that drain line’s flushed out.

George:     Water’s gotta go somewhere off the coil.

Dean:        A lot of times traps need clean outs, now don’t they? So we go in there, we cut out, put a little clean out trap, and you take some compressed air or water and blow that trap out.

George:     Compressed air, brush, anything to run that through to clean it.

Dean:        If water builds up in the trap, it back flows into the unit. If it’s installed properly, it has float switches and all these safety devices, it’s gonna cut the unit off, isn’t it?

George:     That’s right. Everything now has to have some type of safety device.

Dean:        So if you’re getting your unit serviced, and the heat and air guy services it right and he blows out that trap, that’s gonna save you a service call. I had to put my glasses on, ’cause, you know, it’s just the way it is when you get old. So I gotta box here, it says ENTDB. Give me 30 seconds, tell me what it is.

Delta T

George:     ENTDB is the interior dry bulb temperature. That’s the temperature inside your home, the air temperature itself.

Dean:        So that’s the return air?

George:     That’s the return air.

Dean:        All right, we got a return.

George:     So we will take the reading in the return air, and then we’re gonna take the temperature in the supply.

Dean:        So we gonna do that under the house or in the attic?

George:     In the house, under the house, in the attic.

Dean:        And we gonna find the difference.

George:     We’re gonna see what the difference is.

Dean:        What if your air conditioner’s on 70 degrees, and you still feel hot and sticky?

George:     Well, then you have what’s called wet bulb reading. And that’s how much moisture is in the air. Pretty much what the humidity level is in your house.

Dean:        Now why do I care if the moisture level’s high in my air condition system? It says 70 degrees, I’m supposed to be comfortable, George.

George:     You can be, but if you have high humidity in the house, then it’s not gonna be comfortable.

Dean:        Okay, so what would you consider to be high humidity in a house in North Carolina, Raleigh?

George:     If your humidity level is 65, 70, 75% humidity in the house you’re gonna feel-

Dean:        Have you ever been in a new house and it was 70 degrees humidity?

George:     Yeah.

Dean:        Wet bulb, dry bulb, all this stuff tells a story.

George:     That’s right.

Dean:        So it can tell us that maybe it was a bad installation from the beginning. And don’t you think it doesn’t happen. It does happen, a LOT.

What is an Evaporator Coil?

An evaporator coil changes refrigerant from liquid to gas in your AC unit. This evaporation technique soaks up large amounts of heat from inside your home, creating a cooling process. (Remember how awesome 8th grade science was?)
Usually located in the crawl space or attic, the evaporator coil is pretty much the opposite of a condenser coil. The evaporator absorbs heat from inside, sending it to the condenser which expels the heat outside. Getting rid of heat inside leaves cool indoor air, thus giving you that sweet, sweet air conditioning.

Evaporator Coil Checklist Procedure

1. Locate under the crawl space or in the attic.

George in crawlspace
The evaporator coil will be in the same area as your blower motor.

2. Clean Coil

Side view of an Evaporator Coil
Since dust, animal hair, and other debris can affect airflow through the indoor evaporator coil, it needs to be cleaned just like an outdoor coil. But instead of a hose, we’ll use a spray bottle, compressed air, or even just a regular brush.

3. Check Coil Fins

George_crawlspace evaporator coil
Unlike the outdoor coil, the coil inside shouldn’t have bent or crooked fins, unless someone has been inside and messed them up. We’ll make sure they’re okay, just in case.

Delta T

In chemistry and mathematics, DELTA refers to the difference between two measurements. “T” refers here to temperature.
Delta T is the difference in the air temperature after it passes through your AC unit. This will indicate if your unit is running efficiently. Normally you want your Delta T to be between 16°F and 22°F.

Delta-T Procedure

return vent dry bulb reading

1. We measure Delta-T inside your home by taking a temperature reading at the return vent.

Dry bulb reading_supply vent
2. Then a reading at the supply vent.
George_checklist_supply vent
3. Finally we calculate the difference between them.

Dry Bulb Reading

When people talk about the temperature in a room, they’re technically referring to the dry bulb temperature. It’s called “Dry Bulb” because the ambient temperature is read by a thermometer not affected by air moisture.

Wet Bulb Reading

We take a reading of the moisture in the air, indicating the humidity level in your house. High humidity inside won’t be comfortable, even if the AC is blowing at 70°.
In Central NC, indoor humidity over 65% is too high. Even new homes can often have a humidity level above 70%. This could mean there was a bad AC installation in the first place.

– Tip

Keep your unit on “Auto”. Leaving it set to “On” all the time won’t give it a chance to get rid of the moisture that collects on the coils, and instead the fan will keep blowing that moisture back into your house. This adds to the indoor humidity, making your unit waste more energy to make you feel comfortable.

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