Normal A/C on / off cycle durations?

Is there a general rule-of-thumb for how long an air conditioner should run and how long it should stay off? I realize this probably depends on a variety of variables, but is there a rule-of-thumb. I've searched quite a bit and can not seem to find an answer.
If it helps, my house is 1 story, 2400 sq ft. I have the thermostat set at 78. It is 85 degrees outside, humidy 72%.
Right now, my a/c stays on for 8 - 10 minutes and goes off for 7 - 9 minutes.
Thanks for your help.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
glynndaddy wrote:

At those temps and TSTAT setting the unit is short cycling! Each time it starts a run cycle it takes nearly 5 minutes to reach its optimal cooling capacity at those temps and humidity levels.
Where is the RM TH located? Maybe it needs shielding from cool air streams, etc.
They should make a digital RM TH that has an on/off temp differential setting. You could then set it to cycle on at 79 and off even a low as 73-F. Use large floor fans to keep the air circulating as this will add to your comfort. Take a look at the "Human Comfort Zone Chart," on the linked page below.
The way most RM THs are now is that they have a cooling anticipator that aids in keeping the temperature very close to the TH setting. That is the wrong way to go if you want and need longer cycles to reduce humidity levels and increase the operating SEER levels.
- udarrell - Darrell
--
Air Conditioning\'s Affordable Path to the "Human Comfort Zone Goal"
http://www.udarrell.com/air-conditioning-total-heat-enthalpy-latent-heat.html
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

yeah, what darrel said plus, my thermastat has a 1 or 2 degree differential setting. The 2 setting makes it run longer between cycles.
This time of year, in the hottest part of the day, a well designed system should be running just about all the time.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
78f 72% humidity is not a comfortable setting. Your thermostat might have a setting to increase cycle time, a longer time is also easier on the equipment.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
m Ransley wrote:

I believe the OP was referring to outdoor humidity, not indoor. Were it 72% humidity indoor I think the OP would be complaining of problems other than short cycle times.
Pete C.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Thanks to everyone for your help.
Is a thermostat, TSTAT and RM TH all the same thing?
If a properly running systems run for long periods of time, doesn't that translate to high energy bills? What would be a reasonable ratio of on to off time?
I didn't want to take much of anyone's time, but I guess I should disclose that my system is not running right. It was installed in a new house four years ago. I've had to have the system recharged 3 times, the last time a few weeks ago. The previous two times fixed the short cycling, but not this time.
The AC company found a leak in my evaporator coil. I guess it needs to be fixed, but it's going to be expensive. I was hoping that the recharging would buy me some time, but i guess the leak has gotten too big.
Lastly, when they found the problem, the guy did not reseal the evaporator coil housing access panel. I just went up in the attic and noticed there is some cold air coming out. I guess i will get up there with duct tape, but I can't imagine it having that big an effect. There is also air coming out of my drain pipe (because there is no cap on it). I guess I will put some tape on that too.
Thanks everyone.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

NEVER USE DUCT TAPE! Use foil tape as it will last. Duct tape will fail over time.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
replying to glynndaddy, Denco AC - Carrier Dealer - 28 years experience- Licensed in Texas wrote:

A refrigerant leak will have a huge impact on run time. The lower it gets, the longer it will run. Adding more Freon will never solve the problem. A a/c system is like a car tire in that it is air tight. If your car has a low tire it is because it has a leak, adding air does nothing to repair the tire or the leak. The same rule applies to a a/c system. If your unit is 4 years old it should still be under warranty by the manufacturer and a repair would cost you labor and refrigerant, The coil would be replaced by the manufacturer. The leak will only get worse. And in time I running the system low on refrigerant will/can destroy the compressor. As for run time, the length a ac unit runs is determined by variables such as outdoor temperature, heat gains through windows and doors and the amount of insulation in your attic. These same variables determine the length of tine the unit is off. I just a had a conversation with a customer who's old system ran non stop, we installed a new system one ton larger and now it runs 6-7 minutes and is off for 14-16 minutes. So the run time is 18 minutes per hour instead of running 20 hours a day like the old undersized unit.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
replying to Denco AC - Carrier Dealer - 28, Vld5491 wrote:
Denco - AC - Carrier dealer you know I am from California and just had a new AC condenser, coil and furnace replaced. I am experiencing exactly the same as one of your customer after upgrading my AC to a 4t from a 3t unit, it now running like 8-10 mins and shuts down from 18 - 22 mins. But I was wondering cause I have not seen my electric bill after this installation, would this lower or raise my electricity bill?Thanks
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Saturday, May 27, 2017 at 1:44:15 AM UTC-4, Vld5491 wrote:

If it's doing that when temps are moderate, it's probably fine. If it's doing that when temps are hot, then it's oversized. Was there a problem with the existing 3T not cooling enough? What was the reason for going larger? As to the electric bill, probably won't make any significant difference due to the timing. It will use less electricity if it replaced an old honker. The big downside to oversizing is that it won't run enough to remove humidity on moderate days, won't run as long as it should to mover air around and get balanced, etc.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
replying to trader_4, Vld5491 wrote: We decided to upgrade from 3t to 4t because we have a townhouse with 1708 sqft. We had to close 3 registers/vents to get out 3 bedrooms to get to comfortable level. Plus the contractor says in every 400 sq ft requires 1 tonage. With regards to humidity here in CA we have a very low humidity and we are still on moderate weather, summer starts in June. Another thing that came to mind is the frequency of the ac going on and off. Is this not bad for the unit? Well the ac cool up pretty fast comparing to our old honker that's for sure. Thanks for your infos. Have a wonderful memorial weekend😁
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sunday, May 28, 2017 at 5:14:05 PM UTC-4, Vld5491 wrote:

3 tons should be plenty for 1700 so ft.
We had to close 3 registers/vents to get out 3 bedrooms to get to

Probably because something is wrong with the system, design, etc.
Plus the contractor says in every 400 sq ft requires 1

That contractor is an idiot. Following that logic, a 2500 so ft house needs 6 tons? A 3000 so ft needs 7+ tons? You can do a manual J calculation whi ch factors in size, insulation,windows, exposure, climate to get a correct number. That's why you have a system that is short cycling.
With regards to humidity here in CA we have a very low humidity and we

came

the

It's less stress on the system and more energy efficient if it's correctly sized, that's true. But it doesn't mean that it's going to burn up or use a lot more energy either. I'd be more concerned about having it run enough t o get an even temp.
ell the ac cool up pretty fast comparing to our old honker that's for

?

a-c-on-off-cycle-durations-128958-.htm
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 5/28/2017 7:22 PM, trader_4 wrote:

I have 2100 sq. ft. and cool it with 2 1/2 ton. Of course, conditions vary and the contractor should have run the manual J calculations. http://www.loadcalc.net/ http://www.wikihow.com/Calculate-BTU-Per-Square-Foot#Determining_the_Correct_Cooling_Capacity_sub

Agree on the idiot part.. Looks like the OP will have a cold muggy summer.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
replying to trader_4, Vld5491 wrote: Thank you so much for the infos. Have a nice day😁
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
JimL wrote:

No matter how hot it is, it can get hotter. I would say a well designed system should be running _most_ of the time; you never want to run out of reserve. If it's at a 50-60% duty cycle, it'll be effective removing the humidity.
--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form snipped-for-privacy@prodigy.net.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

No,No. You DO want to run out of reserve. A well designed system should fall behind on the hottest day of the decade. It won't be able to keep up. Your thermostat will be set at 78 but the temp will creep up to 80, 81, 82...... etc.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
JimL wrote:

With global warming, the next summer it'll be 90, 91, 92 ...
--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form snipped-for-privacy@prodigy.net.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Thanks to everyone again for your help.
My builder has contacted the AC contractor who installed the system and they've agreed to replace the evaporator coil. I hope they do a good job. Last month my bill was $270 to cool 2400 sq ft to 79 degrees.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I was just looking at warranty period on Goodman coils and the standard warranty is 10 years on the coil with a new system and 5 years otherwise. Lifetime on the heat exchanger.
Good for you on getting a new coil. I suspect a botched install, not a bad coil.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
CJT wrote:

I know from BITTER experience that you do NOT want a AC system that runs from 10:00am to 10:00pm. Power bill DOUBLES. House is livable, but uncomfortable, especially when guests are over.
50% duty cycle, but no more than once an hour, certainly no more than once every 30 minutes. Any faster cycling than this is dangerous for the compressor.
A house that is 'adequately' plugged against air leaks, and has 'adequate' insulation should not have a duty cycle of greater than 50% and really should have a duty cycle of under 25%. Air leak plugs are the new hot button, now that most new homes have at least R38 in the ceiling and R24 in the walls, Course if we do manage to plug those uncontrolled air leaks, then the house accumulates odors (cooking, body odor - human and pets, solvents, cleaning fluids, paint, plastics......) and we must then install a controlled ventilator.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.