[AKaeTrue]

This is an upstairs 2 ton unit for aprox 1300/1400 sq ft. (central)

Old unit (same as above) use to get the upstairs as cold as we wanted,
But so far this summer it did not,
After repeated service to the unit w/o any improvement,
We had it replaced.

The old unit started running non stop and could not cool the temp
Lower than 77 F, and now the new unit is doing the same thing.

Had another AC guy come out for a second opinion, he said the unit is working fine and giving all it's got. He said that it's just because it's so hot outside.

We are just at the beginning of our summer and it's going to get a lot hotter! We never had to fry before because the weather is hot outside.

Does anyone have any opinions on this or what could be happening and why two professional AC guys cannot find a problem?


Thanks, and sorry if all the info needed is not here.
Let me know what you need to know and I'll get it to ya:D Thanks!

[twinkiedooter]

I think the unit is not big enough. How big was the other unit - the old one? Sometimes having to properly cool down a two story home is a headache. What did they say about the size of the new unit being able to cool down the house properly?

[hvac1000]

Rule of thumb is 600 square foot per ton of cooling. Since this is in a upstairs setting a little more additional is OK. You are a little short on the BTU side.

Can you insulate your attic?
Can you add a roof fan to draw the heat out of the attic?
Is the duct in the attic insulated and TIGHT in its construction?

Years ago we used to calculate a 6000 BTU savings on the size of a unit by installing a attic fan.

What I am telling you here is not near as accurate as a manual J done on the structure but a guestimate.

[AKaeTrue]

Thank you for the responses.
The second AC guy said the upstairs could stand for a 2.5 ton unit.
But that the entire system in the attic would need to be replaced to go with it and that would cost a lota lota money.
He said that we'd be able to keep the temp more comfy if we install an attic fan, so we'll be looking into that.

I've been brain storming every since on how this can be and it finally came to me.
Last fall we had 3 huge trees removed that were literally on top of our house tearing it up. I guess those trees acted like a huge sun visor.
Now that they're gone there is no shade and the sun is beaming down on the roof and house.

*sigh*

Thank you so much for your time :)

[azacdoc]

Now you've discovered the problem, which sounds correct. I do want to take issue with the 600 sq ft per ton thing. I've never worked back east but as I understand it, it's 400 sq ft per ton everywhere in the country. I have heard of people in Oklahoma using units that are too small to act as a dehumidifier but this is still undersizing regardless of climate and they break down constantly because they're running their little hearts out.

400 sq ft per ton.

[hvac1000]

In this area it is 600 sq ft per ton.

Many A/C units are oversized and do not have a chance to do there main job and that is to dehumidify. Once the water is gone you can be comfortable at a much higher temperature.

The answer was also qualified as per below.

No one in there right mind would really use the square foot per ton guess game.

What I am telling you here is not near as accurate as a manual J done on the structure but a guestimate.

[azacdoc]

Their "main job" back east is to dehumidify. Here in AZ, it's to remove heat, not moisture.
I'm quite familiar with 'higher temperatures'. I'm wondering what you're thinking is "higher".

Yeah. The world works by Manual J doesn't it... (ha)

[mtyogi17]

I'm in South Florida and I just installed a Trane XR13m 3 ton package unit for 1156 sq. ft under air. This is what we need down here in the Sunshine State. So I agree with 400 sq.ft.per ton.

[azacdoc]

If the idea that 600 sq ft per ton worked, he wouldn't be having a problem.

Thanks for the comment.

[hvac1000]

This area runs up to about 95/98 degrees during the summer but that temp is not all the time just for a few weeks. The best way to size is a manual J if you know what that is. All else is a guess.

Most folks that post here to help have some common sense and knowledge. No one here knows it all especially myself.

[hvac1000]

Talent hits a target no one else can hit; Genius hits a target no one else can see.