AC running alot

[jamie]

Hello all

Question, I have an AC at a customers house , 2ton  13 seer AC with a modulating goodman furnace, CTK04 thermostat,

The customer says the AC ran all day today. Thermostat is set to 22, he said never went higher. It was hot but not too hot. I went in the basement and noticed there was a Aspen case coil installed , its a 4 ton coil. The thermostat is set for 3 ton cooling speed.

Normally we go up a ton if we install a 16 seer AC, ive never seen a 4ton coil on a 2 ton ac haha

Could that be the issue?? oversized coil? the airflow seems good upstairs and i was getting a good temperature difference.

Any help would be appreciated

[walker]

what was the air flow set too?

grossly oversizing the evaporator coil will result in piss poor humidity removal.

[Admin]

Is it a Goodman AC?  There was a time when a 13 SEER AC with oversized coil and ECM furnace would achieve a higher SEER to qualify for rebates.  What size is the house?  I would check the refrigerant charge.  Is there a TXV installed on the coil?

[jamie]

air flow was set to 3ton (its all done in the CTK thermostat) I don't normally run into these.

The house is about 2200 square feet or so. AC is a keeprite that was installed about 6 years ago, furnace and thermostat new this year. NO txv valve installed on the coil

ya it seemed to keep it at 22 but kept running and running, maybe not removing any humidity?? would it stay at desired temp if it wasn't removing humidity?

[walker]

I would drop the air flow back down to 800CFM.  The oversized coil with too high air flow is going to result in not so good humidity removal and low temp drop.

[jamie]

you think down to 800cfm? seems low for a 2 storey home. The airflow upstairs seemed to be the issue which is why the customer changed furnace (although furnace was 20+ years old)

[walker]

air flow for cooling isn't set by the number of storey's in the home. If the equipment and duct work is properly sized and sealed there should be no problem cooling the home with 800CFM.  at 1200CFM all you are doing is removing less heat and humidity from the air.

[jamie]

the house is super old so was probably sized properly in that time. I will give that shot. if that doesn't help do you have any other ideas? size the coil properly??

[walker]

Some measurements will help.

txv or piston, indoor wet bulb, OAT, gauge pressures, superheat and subcool.

[harshal]

You would need all the readings to understand the system .I would take suction ,discharge ,wet bulb and outdoor temp and decide further action.I would try to match up indoor coil to outdoor unit. If they have 4 ton coil but piston size may be for 2 ton or 2.5 ton coil.air conditioning is more about the dehumidificatiobn so 800 to 1000 cm ideal for 2 to 2.5 ton.sonetimes I set 350 cfm per ton.

[DaveP]

The house is about 2200 square feet or so.

If that's ground and second floor, I certainly would not have put in a 2 ton. Has this thing ever cooled the house properly?  Hate to see what happens on a "too" hot day.

[walker]

Where are you located, just wanted to point out Toronto design temperature is 30C.  And it was close to 30C the last few days, in theory the A/C would run all day at design temperature.

[Hvacpimp]

Those communicating thermostats are brutal when it comes to cooling. You can try everything on the tstat and dip switches to bump up the blower speed. Do yourself a favour and put on a regular thermostat. The airflow will be higher. Had that same issue a number of times last summer.

[Hvacpimp]

Also, 3 ton on a 2200sq/ft house. Way too big. I would try to change the stat first. It sounds stupid but try it! Put a cheapie on for now just to test!

[Hvacpimp]

I would have went with a 2.5 ton. Sorry I thought u said 3 ton ac, I didn't read 2 ton with 3 ton air flow. I had a customer call me with the exact same problem and square footage as you are mentioning except his wouldn't go lower than 24 and always running. We installed a 2.5 ton and boom goes the dynamite. It worked! Try changing the stat first, than maybe break the news that he might be up shits creek!

[Porcupinepuffer]

If it does turn out that it's just a bit undersized, I'd check if he has a basement and I'd have him close off the dampers for all the supplies to the basement.

[Admin]

It's hard to believe an AC running that much would leave high humidity inside, which is usually the cause of sweaty ductwork.  Make sure there is no outdoor air supply piped directly into the return air duct.

Check the difference in temperature between the return and supply ducts.  If the difference is higher than 19F we would raise the fan speed to lower the difference.

[walker]

the temp drop will vary based on return air wet bulb

go here and punch in your return air wet and outdoor dry bulb and it will give you the expected temp drop.

https://hvacrschool.com/resources/delta-t-superheat-calc/

Also do yourself a favour and get the measurequick app, it can be very resourceful and help guide you through problems.

[Admin]

How do I get pressure readings on this app?  Do I need to have digital gauges connected?

[walker]

You can enter them manually or they will connect with Testo smart probes or iconnect probes.