Does central air conditioner work less efficiently when it's hot outside?

Question

I have a new central air conditioner. Normally, it cools down the house 5 min per degree, so it takes around 25 min to lower the temperature from 80 to 75 degrees upstairs. I have 2 floors. Today, I went out to run errands and didn't get back until 1pm, when it became 91 degrees outside and 85 degrees inside. I kept the AC on for several hours, and it didn't cool the house below 78 degrees until 9pm.

Does the AC work less effectively when it's really hot outside, and the coils don't cool off very fast in 90 degree heat? Is that why it didn't go below 78 degrees inside till night time?

Is there such as thing as a super-hot day when even a 3.5 ton AC gets overwhelmed? Is there any point to "staying ahead" by turning the AC on at 11am if we think a hot one is coming in order to start cooling earlier before the house gets really hot?

Answer 1

Well it seems the only one who had a clue about this question was Neil.
It isn't necessarily harder to cool your house when it's hotter outside unless you have let your house get very hot and humid inside. Most a/c units are designed to cool the house 15 degrees cooler than outdoor temp and you should never set the thermostat more than 20 degrees cooler than outdoor temperature or risk damaging the unit. Ideally the air coming out of your registers will be 18 to 22 degrees cooler than the temperature in the room. It's always a good idea to draw the shades whenever possible to avoid direct sunlight heating your home during the day... this will help the a/c catch up and also keep your electric bills lower. As you mentioned, it is best to close the windows and turn on the unit early in the day if you know it will be a hot day. This will actually cost you less in energy and prevent the days heat and humidity from building up just to be removed later. Keep basement and upstairs doors closed if possible, to keep the cool air where you want it. The upstairs does not necessarily have to be warmer than the first floor if the house was ducted properly and the system balanced. Use ceiling fans on low speed to help move the air... you will find that with the air moving you can set your thermostat a couple degrees higher and still feel comfortable. Heat does not rise... hot air rises as it is lighter than cool air. Heat in itself will always seek cold to find an equalibrium.
A systems tonage has nothing to do with airflow but is the cooling capacity of the unit. This term goes back to the days when ice was the only source of refrigeration. 1 ton of ice can absorb 288,000 btu's of heat... divide that by 24 hours in a day which equals 12,000 btu's. Therefore a 1 ton system is rated at 12,000 btu's per hour. Your system is a 3.5 ton, so it can absorb 42,000 btu's per hour.
If you think the system isn't cooling as it once was, first check your filter to be sure it is clean. Change it if necessary. If the system still seems off to you, then call a technician to tune up your system.
I hope this helped you.

Answer 2

Only the last 2 answers made sense,however u stated that your a/c can cool 5 degrees per minute and in less than 25-30 minutes you'll cool down 5-6 degress' i don't like the sound of that a/cunit could be oversized or in this case it sounds like u have great attic and house insulation added after the original install.If u did update the insulation make sure the attic has proper ventalation.The problem is we as HVAC Pro;s will say your a/c is fine and it's just hot outside,the truth is yes it will work a little harder but still should reach the temp. u set it at and this is called ENERGY MANAGEMENT something not alot of Pro's or homeowners know. Go with your gut feelings if u feel somethings not right call a HVAC Pro that specializes in energymanagement to do a load calulation on your house and make sure alls ok it's worth the money and you'll be surprised by the results.Also check filters every month and make sure no airflow is blocked or covered up.

Answer 3

All air conditioners can be over-whelmed by the heat.
During the day I set our central air to 74 degrees, at night (around 10pm or so) I change it to 76 so that if by some chance I sleep in, the house doesnt end up super hot. If I wont be home during the morning I will keep it set at 76 so that when I do get home its already cool, no waiting for it to cool off.
When we are up and I know it will be hot I move it back down to 74, if it will be a cooler day, then I leave it where its at.

Answer 4

May I say that Tsunami and Sean P. are very good answer's to your questions.
I would like to add to Sean P. remark that not only change the filter and check it once a month but, also take your garden hose and starting from the top, spray slowly from left to right your fins on the condenser unit (outside unit) and slowly move your way down. Do this all the way around the unit. Remember that by keep the condenser and filter clean, the more efficiently and better the unit will run.

Answer 5

The "tonnage" of an air conditioning unit, actually refers to how much volume of air, it can replace. Not how 'powerful' the unit is. All air conditioners, will typically blow air that is only 15 degrees cooler than the air it is using as intake. So.... if your system is cooling on a day with 80 degrees... you can expect it to be blowing air that is 65 degrees, thru the vents. On a 100 degree day... your system will only be blowing air that is 85 degrees. As the day cools... the actual temperature coming out of the vent will drop too. Now, remember... this is just the temp of the air coming out of the vent.... it will take time to replace all of that 85 degree air inside your home... how fast it replaces it, is according to how much volume your system is made to handle.

Your air conditioning will work better, if you leave it on, but if you do not want it set to keep the place too cool while you are out... simply turn up the thermostat a bit. Then...like on a day when you are taking a bit longer to get home... the system will go ahead and kick on, at whatever temp you preset it at.

Have Fun!

Answer 6

Air conditioners have factory designed working temperatures, 75F- 95F meaning anywhere below or above these temperatures, efficiency is lost and they dont operate as well, so on a 100 degree day if your thermostat is reading under 80 degrees inside the house ,praise the ice gods you have a good a/c system. Check your filter make sure its clean, make sure your outdoor unit is clean. Have the refridgerant checked, sometimes the factory charge isnt correct, or if its r22 they might not have charged the unit correctly, was it a cool or cold day when they installed your new unit? It happens!

Answer 7

I think you're asking for ways to help your a/c work more efficiently. You can close doors and windows earlier in the morning and draw curtains to prevent heat coming in from outside. Set your thermostat to 24 degrees C [75 degrees F]. The warm air has to be pumped out and fresh cooled air pumped in, then set the a/c control to "recycle air" [or whatever] when the temperature inside starts to fall. Does your home have insulation in the walls and ceiling?
ANSWER - The a/c works harder to keep you cool when it's hot outside.

Answer 8

since heat rises the second floor will always be hotter than the ground floor good in winter time bad in summer time. a.c. only takes the moistour out of the air first then will cool the housedown gradually. set it no more that 5 to 10 degrees coler than the outside ir so it won't have to work so hard. think about putting a seperate unit in the upstairs as tis is more effenct to keep the upstairs comferable in hot weather.

Answer 9

Central air

Answer 10

you are proably setting the temp to low at start up.If it's already hot you need to gradually lower the temp to keep the unit from freezing up.And yes it is harder to cool the hotter it gets outside.you could be getting "stored heat" through the windows etc,,that are exposed to the sun and also in the attic.