Normal A/C on / off cycle durations?

[Tekkie®]

Uncle Monster posted for all of us...

was short cycling. Most of the posts here were about what temp is comfortable and other useless information. I love the "wrong again" comment. That was also helpful especially without a reason. I'm pretty sure my one year old, 7K, 2.5 ton system is too big for my 720 square foot house. I had the compressor and outdoor components exchanged for 2 ton components within two weeks. The humidity is always in the upper fifties so it never feels good. Another sign it's too big. Not surprisingly, the blower motor went out at 12 months. I was lead to believe it was a manufacturing problem. Doesn't take a genius to figure out a system turning off and on too often will also cause wear and tear. Which leads us back to the original question....how short is too short? It was hot here in Chicago yesterday, 85, and my newly repaired A/C was on 7 minutes and off 7 minutes which I felt was too short. Still at a loss given the info here. It was hot, am I wrong in thinking it was too short? BTW, I realize insulation, window and door leaks must factor in. Four years ago I had 8 inches of insulation blown the attic. My old two ton A/C never had such short cycles, not even with 4 inches of insulation. I understand on a hot day 10 minutes on and 10 minutes off or three cycles an hour could be appropriate from info I got elsewhere. Anyone agree? Comments? I can't replace worn out parts every year.

BINGO BINGO BINGO +500

[Ralph Mowery]

installation and repair. ?(?)?

There is a program called Manual J that should be ran to calculate the size of you AC. It usually runs about $ 100. The AC guys should do that for you.

Here is a link to an online calculator. I have not tried it as my AC seems to work fine.

That 2 to 2 1/2 ton unit seems to be about 2 times as large as it should be unless you have almost no insulation and are in a very hot area.

I only have a 2 1/2 ton heat pump in a house that is almost 3 times that in the middle of NC.

[Wayne Boatwright]

On Tue 19 Sep 2017 02:44:23p, Ralph Mowery told us...

We live in a 1500 sq ft condo in central Phoenix AZ. Obviously our heat load is significantly different than the OPs. I believe our AC unit is 3 tons, and we typically maintain 77? F. 24/7. On average I think our unit cycles on and off every 15 minutes.

[Jminter80]

replying to Wayne Boatwright, Jminter80 wrote: Honestly there isnt one answer for every situation but your unit should run enough to keep humidity at acceptable ranges. The person with the 800 sq ft house is going to have issues with humidity due to size of house and 2.5 ton is most likely oversized. Depending on insulation and windows your looking at a 1.5

- 2 ton unit. Run cycles will change with the temperature outside as well as humidity levels. Best thing to do is set indoor fan to circulating mode if that option is available to keep air moving due to the size of the house also you should be able to adjust speed if it sounds like a jet. There are more options besides smaller system. The off cycle is going to be effected by how well the house is insulated as well. If its not insulated well than your house is going to heat up faster when the ac is off therefore ot will cucle more often. Also I am not sure how much saving you anticipated on an 800sq ft house because ot doesnt use enough energy in the forst place to allow for a noticeable change either way. If it were a 2500sq ft house with a $400 electric then you could expect a noticeable saving by updating to a newer and more energy efficient system. Think of percentages when dealing with savings also which means 10 percent of $100 is less than 10 percent of $400. Back to run time....unit should be sized properly to have a long enough run time which in my opinion is 5-10 minutes to properly remove humidity and off time should be around 20-35 minutes. This varies because an old house will gain heat faster than a new well insulated house. There is also room for error on sizing due to all the variables and size of home which I always lean to the 1/2 ton larger side for the abnormally high temps we experience for a week at a time in southern Illinois. Never have had one issue with run times or humidity. My last customer questioned it running every 30 minutes but he came from window units and thought that was to much but you have to also factor in the comfort throughout home which means a customer shouldnt feel swings or hot spots. It should stay the same temperature all the time regardless if its running or not unless you are directly below or above a vent. If it gets really cold when the unit kicks on then warms up after it kicks off then your unit is oversized plain and simple.

[tsjdan]

My situation even tho it would appear to be short cycling isn't quite accurate. My issue is run time. Typically as if now in AZ it's 90 pit and run time is 5 minutes and off time 17. So this truly by definition wouldn't be short cycling would it?. Anyways I've known for years system is indeed oversized and tried to compensate with my lux swing settings. Usually kept set at 2 with set at 77. It's just becoming uncofortable though as temps per display shows 78 when it comes on even though should be 77.50. Anyways today I'm trying something new, set temp for 76 with a 6 swing. Run time now is 17 minutes with off being around 15. Air feels much more comfortable yet worried now on $$ as times are tough. Last thing I want is a more $$. SRP bill shows $170 this month estimate thus far... That's with my normal 77 with 2 swing. Anyways I wanted to ask you guys how would you best handle this issue. Short cycling doesn't quite point to my issue I suppose to the letter. How old you guys handle this?.. not enough funds for new AC unit and not wanting crazy bulls either, but don't want to feel like I'm in a fireplace either. Thank you all for any ideas or suggestions on this. Bless.

[Ed Pawlowski]

Something does not sound right. More run time will remove more moisture and increase comfort. Of course as you already know an oversized unit does not run as long to get the temperature down. More run time also means higher cost.

The 6 degree swing will increase run time giving you at least temporary comfort, but the off time would be increasingly getting uncomfortable. It then has to work harder to get to the low setting. I think as long as the AC is blowing dry air you feel comfortable.

As an aside, many years ago my father was the plant engineer at a printing plant. Humidity control was important and on cool damp days it would be very high. They would run the heat and AC at the same time to maintain both temperature and low humidity. You can do that too, but obviously it would be very expensive.

[Dan]

Thanks. The 5 minutes run was when it was 77 with 2 swing. Seeing that isn't much run time, i changed it to 76 with 6 swing to increase runtime.. which it worked, ran 17-20 minutes. why 76, well we want to keep house at 77, so to simulate that yet allow more run, i did 76 with 6 swing, which should place it at 77.5. The off time tho is quite large. Just trying to find a happy medium where it will run longer to condition air better, yet not kill us in $$ or tax the machine to much. from all i read to properly work efficiently it needs to run 10 minutes or more... Our air always feels well not crisp in the house, hence why also i changed it to run longer and that has worked.. but the off time is rough....

The system is older... 9 years... house is 1100 square feet and the builder placed a 4 ton here.... yes 4 ton, and its way over sized of course.... hence my issues. have to make do as money is tight, so trying to be comfortable and yet save money and baby the ac. Sorry if my post is a bit confusing, i have been dealing with this for a long time to find that sweet spot and its driving us crazy...... thank you for your time.

[Dan]

For clarification.. With the lux the swing is

1 = .25 2 = .50 3 = .75 4 = 1

so when I did 6 swing at set 76 that would have been 77.5F etc..

[trader_4]

I don't understand that math. Doesn't 6 swing mean it turns on when it's

3 over and off when it's 3 under? That would still average it at 76.

The off time tho is quite large. Just trying to find a happy medium where it will run longer to condition air better, yet not kill us in $$ or tax the machine to much.

There shouldn't be much difference in cost if it's still keeping the house at the same average temperature.

from all i read to properly work efficiently it needs to run 10 minutes or more... Our air always feels well not crisp in the house, hence why also i changed it to run longer and that has worked.. but the off time is rough....

Yes, that's for sure.

hence my issues. have to make do as money is tight, so trying to be comfortable and yet save money and baby the ac. Sorry if my post is a bit confusing, i have been dealing with this for a long time to find that sweet spot and its driving us crazy...... thank you for your time.

It can't be that hard. There isn't much you can do except trade off more temp fluctuation for run time.

[Dan]

A swing of 4 is 1 degree .25 increments. so set at 76, a 6 swing would be 77.50 and after run off at 74.50. Lux lists swing as

Swing Setting

1 +\- .25 F

2 +\- .5 F

3 +\- .75 F

4 +\- 1.0 F

5 +\- 1.25F

6 +\- 1.5 F

7 +\- 1.75 F

8 +\- 2.0 F

9 +\- 2.25 F

Example: For tightest control, set swing setting on # 1 which is plus or minus .25 degrees F. If you set the setpoint at 70 F, the highest it will get to is 70.25 F, the lowest it will get to is 69.75

Example: On swing setting # 8, if setpoint is at 70 with swing of plus or minus 2 F. Highest it will go to is 72 and lowest it will go to is 68 F.

the only reason I went to 76 from 77 is a swing set from a set 77 gets to warm in here... as a swing from that set is taking me into 78+ territory (assuming i want longer run times) .. hence why i went to 76 and did swing from that point so we can get longer run times, yet remain under 78.

Not sure if this the right way to do it.... yet my circumstances here arent ideal. the stat is even in the hall way below the return vent... horrible placement causing issues there in its own right. I have been looking at those stats that allow me to have a sensor in another room, would love for it to be in the living room and not in the hall with the return vent.

[George]

I run a separate dehumidifier to remove the humidity and let the central AC run as needed to regulate the temperature.

Run a ceiling fan and you can set the AC thermostat higher and still be comfortable.

[CRYSTAL]

I just got a new ac unit installed i set the thermostat on 70 well it don't feel like 70degrees and it will cut on and run for exactly 3minutes and stays off for 20minutes before coming back on for 3min can someone please help me on what you think it could be please

[Ed Pawlowski]

Could be a lot of things. Bad thermostat, not properly charged system, something overheating, Oversized system. What is the thermometer reading?

If it was just installed, call the company back and let them sort it out. You paid for a proper system, let them fix it.

[Larry]

Maybe you should ask the install company?

[trader_4]

To the above, I'd add the most relevant piece of info is missing. What it feels like is one thing, but what does the thermostat actually read? What temp is it really? If it's 70 and doesn't feel like 70, could be it's humid and they need to lower it to 68F.

[Tekkie©]

On Mon, 16 Aug 2021 18:15:02 +0000, CRYSTAL posted for all of us to digest...

Call the company that you dealt with. Sounds like it may be oversized or the thermostat is bad or mis-located.