It is 104 degrees outside.Should my A/C be able to acheive 78 degrees inside?

Question

I have a 2 story home in Fort Worth texas that was built in 1996. It is in good condition. (ie windows are good and no obvious air leaks) The AC is the original unit. It's over 104 degrees today and my A/C has been running nonstop for days. It is not able to get the temperature down to 78. It's usually around 80 to 81 degrees inside.
I'm from So California and not sure what I should expect out of my AC unit. I would have thought that it should be able to push it all the way down to 72 if I wanted it to, but it can't even do my setting of 78.
Am I unrealistic, or do i need to have it serviced or replaced?
Thanks!

Answer 1

Here's a couple of things:

Your house might have been just on the edge of say a 3 ton unit or a 4 ton unit, and the builder may have put in the 3 ton unit to save him a couple of bucks. It would work fine unless it got really hot, like say 104.

Now, I design A/C for a living, and the calculations are based on the 99% weather data, meaning that 99% of the hours during cooling season are at or below that temperature. The 99% temperature is only 98 degrees. That means that when it is over 98 outside, your A/C will not be able to maintain your thermostat setting. And the more consecutive hours over 98, the hotter your house will get.

During the evening/night the problem is that the roof/attic absorbs heat during the day, and it probably gets to be over 130 degrees up there. When the sun sets, all the heat stored up there starts to dissipate down into your upper story, keeping the house hot.

Even still, sometime during the night, the unit should be able to cool the house.

Answer 2

Definitely have the unit looked at - a 10-yr old unit should still be putting out a better cooling than what you describe. Filters are super-important, as is how well you are insulated. We've weatherstripped everything, put in extra insulation on exterior walls and in the ceiling area--it's 105 where we are today and we're floating along on 77 [which is where we have it set]. If your climate has high humidity like ours, then you might need to consider a dehumidifier in a central location...it made a huge difference for us, the A/C doesn't have to work so hard if you can lower the humidity to right around 50%.

Answer 3

20 degrees difference between inside and outside is probably the best you can hope for. Maybe 25 if your unit is well shaded. If you haven't had the unit serviced in a couple of years I would get someone out there and see if its 1 or 2 pounds low on freon. It won't cost that much for the service and it may get you a few degrees cooler.

I get my AC serviced every year. Its worth the cost to know that you are operating at maximum efficiency.

Answer 4

Most AC techs will say that your unit is fine if it can lower the temp 20 degrees. I'd be amazed if you could get it deep into the 70's, especially if you're running a single unit on a two story house. 104 degrees is just damned hot...

Make sure that your filter is clean and that the coils on the condenser and evaporator have been cleaned, and that the unit has a full charge. All of these things can lower a unit's efficiency.

Answer 5

I'm in central Indiana and we live in a 2 bedroom apartment on the 3rd floor of a 3 floor building...our AC unit needed a good cleaning after this heat wave hit our area. maintenance cleaned both the inside unit and the outside unit. We have it set on 70* and there are some days its runs non stop to keep it cool inside
I would have someone come and look at it...if it needs cleaned (the coils) then have it done because it can end up costing you more later

Answer 6

1. Sounds like you need freon. Call a service man.
If it does need freon, buy a new unit before next summer. There are A/C sales in August. Most A/C are put away in September, so you need to buy one this month OR next spring. A/C are not suppose to lose freon.

2. Most A/C service personnel say to keep the temps at 68 degrees.

3. My husband buys a new unit about every ten years. Our house is always cool. Don't be shocked at the cost, it will be a couple or three thousand dollars.

By the way, we live in semi-dessert West Texas. Welcome to Texas.

Answer 7

my poor old unit was serviced last year, is 12 yrs old , and the other day when we had 104, I had it set on 75, but it couldn't get the temp down past 78..... I think you need service!.... plus... is there an attic?... does it have a vent/fan?...

Answer 8

I think you need service, its really hot here too and our house maintains whatever we set it at.