Author Topic: AC running alot  (Read 2032 times)

Offline jamie

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AC running alot
« on: May 23, 2018, 07:42:57 PM »
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

Offline walker

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Re: AC running alot
« Reply #1 on: May 23, 2018, 08:08:58 PM »
what was the air flow set too?

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

Offline Admin

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Re: AC running alot
« Reply #2 on: May 23, 2018, 08:12:01 PM »
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?

Offline jamie

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Re: AC running alot
« Reply #3 on: May 23, 2018, 08:18:00 PM »
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?

Offline walker

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Re: AC running alot
« Reply #4 on: May 23, 2018, 08:19:49 PM »
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.

Offline jamie

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Re: AC running alot
« Reply #5 on: May 23, 2018, 08:27:24 PM »
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)

Offline walker

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Re: AC running alot
« Reply #6 on: May 23, 2018, 08:36:11 PM »
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.

Offline jamie

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Re: AC running alot
« Reply #7 on: May 23, 2018, 09:25:17 PM »
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??

Offline walker

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Re: AC running alot
« Reply #8 on: May 23, 2018, 09:31:40 PM »
Some measurements will help.

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

Offline jamie

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Re: AC running alot
« Reply #9 on: May 24, 2018, 04:14:53 PM »
There is no txv, its a piston...
I haven't had the time to go back yet, but I was thinking to myself..The coil was installed afterwards with the furnace, they probably didn't change the piston. It may be the 4 ton piston in the coil, and the AC is only a 2 ton. Could be the issue?



I am going to be going back next week when i have more time to to get all readings.

Customer called said its very comfortable in the house, but tstat is set at 22 and says indoor temp is 22 and its been running all day.

Offline harshal

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Re: AC running alot
« Reply #10 on: May 24, 2018, 08:47:17 PM »
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.

Offline DaveP

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Re: AC running alot
« Reply #11 on: May 25, 2018, 08:35:24 AM »
Quote
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.

Offline walker

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Re: AC running alot
« Reply #12 on: May 25, 2018, 09:12:09 AM »
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.

Offline Hvacpimp

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Re: AC running alot
« Reply #13 on: May 27, 2018, 02:55:20 PM »
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.

Offline Hvacpimp

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Re: AC running alot
« Reply #14 on: May 27, 2018, 02:57:38 PM »
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!

Offline Hvacpimp

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Re: AC running alot
« Reply #15 on: May 27, 2018, 03:03:11 PM »
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!

Offline Porcupinepuffer

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Re: AC running alot
« Reply #16 on: May 27, 2018, 06:50:43 PM »
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.

Offline jamie

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Re: AC running alot
« Reply #17 on: May 28, 2018, 10:30:56 AM »
I haven't got back yet to check out the readings, customer is away until later in the week...

All basement registers are closed.
House is located in Whitby so yes its been real hot here lately. The 2 ton AC was already installed before the furnace installation, AC is about 6 years old. Keeprite 2 ton

The customer emailed me, said the temp is still 21 and staying at 21 but AC keeps running all day and he said his plenum is sweating alot. Said its dripping

The communicating stats dont really let the temperature rise which is probably why it keeps running.

Offline Admin

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Re: AC running alot
« Reply #18 on: May 28, 2018, 11:54:54 AM »
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.

Offline walker

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Re: AC running alot
« Reply #19 on: May 28, 2018, 12:56:33 PM »
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.

Offline Admin

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Re: AC running alot
« Reply #20 on: May 28, 2018, 04:13:53 PM »
How do I get pressure readings on this app?  Do I need to have digital gauges connected?

Offline walker

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Re: AC running alot
« Reply #21 on: May 28, 2018, 04:15:21 PM »
You can enter them manually or they will connect with Testo smart probes or iconnect probes.