A/C not cooling below 80 when outside temp is 98. It is a split system, inside & outside coils clean, unit and ducting in house attic, just had ducting replaced and is insulated well, R30 blown in insulation in attic, return is against roof, 3T for a 1800 sqft brick 30 yr old house. What else to do or check?

Probably nothing. Ac units are only designed to cool 20 degrees below the outdoor temp. so yours when new should get dow to 77 or 78 when it is 98 out. How old is the unit? The older a unit is the less effencant it becomes. Do you have a attic fan in your house to pull heat out of the attic?

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Originally Posted by Joshdta

Probally nothing. Ac units are only designed to cool 20 degrees below the outdoor temp. so yours when new should get dow to 77 or 78 when it is 98 out. How old is the unit? The older a unit is the less effencant it becomes. Do you have a attic fan in your house to pull heat out of the attic?

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Unit installed 10-2007 3 Ton split 13 seer system. Just intalled 2 gable fans, there is a roof ridge vent and soffitt vents and a large grill vent at the end of the attic space above the carport that is perpendicular to the house.

I'm having the same problem. Sometimes when it's 87 outside, I have my house temp set on 75 and the house is 78 and will run for 12 hours straight. I don't think this is how an A/C unit is designed to run.

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Originally Posted by Jeni14

I'm having the same problem. Sometimes when it's 87 outside, I have my house temp set on 75 and the house is 78 and will run for 12 hours straight. I don't think this is how an A/C unit is designed to run.

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You are right, if you are sure the furnace filter is clean, and all units are running ,its about all you can do, but call a local hvac tech to look it over,, 12 hours straight is a lot of electricity to be waisted

I agree! It is a brand new unit installed at the end of May. The coil wasn't replaced until early July because no one realized it wasn't compatible, there was a leak in the line from the weld of the new coil and that has been fixed. The filter is only 4 weeks old so probably needs to be replaced, but isn't crazy overdue. Return air is 20 hotter than the air coming out of the vents and the humidity in the house is about 49% so all of that sounds like it's working fine. I'm having someone over tonight to check the TXV valve, but I don't know what to check beyond that. I thought possibly the tonage is too small, maybe? It's a 2.5 ton unit with a 1200 square foot house on the main floor, there is an unfinished basement and garage below the main floor. Any other suggestions?

Are there open supply vents going to the basement and garage?
If so close them off,tape over them if necessary, no use in cooling an area where not needed

Yes, I have taped off the supply vents to the basement, and there aren't any in the garage.

Take a water hose to your outdoor unit. This will help a good bit. The cleaner the better. Do not use a pressure washer.

If your house is insolated well, and I mean really well, with the correct system installed you should be able to keep your home at a comfy 72 degrees on a 100 degree (outdoor temp) day. But at these temps, the unit will run most all day. You should be able to see between 14 and 20 degree differential between room temp and supply register temp if unit is working correctly(in most cases). Sounds like you need to have the system checked by a qualified ac tech. Good luck and please let us know what they have to say.

Definitely need a qualified tech to evaluate... a properly designed & installed unit in a well insulated house with a well ventilated attic should have no problem on 100 degree day... just beware... if the tech also makes commission on sale of equipment... get more than one evaluation !