The thermostat on my upstair ac is going up from 76 to 81, by 11 pm starts coming down to 76 again till next day. The air is cold enough too.The outside temp is 96 to 98 in Ga.

 

It sounds like the AC cannot keep up. As the heat of the day soaks into the house the temperature gradually rises. Then when it cools outside the AC gains ground and returns the house to the set temperature.

 

Yes it does.Does it need a freon?

 

Look online how to test by measuring the air temperature going into the return and what's coming out of the register. It's possible that your unit has some problem like low on freon.

Have you installed a clean air filter?

 

You should also look into excessive heat in the attic. Your attic needs fresh cooler air in and a way to get rid of the hot air. Look into soffit vents or possibly an exhaust fan.

You may need more duct insulation too.

 

I have the soffit and exhaust fan is runnihg most of the time no wind or air when outside is 110.And I have changed all the filters as always(my first lesson I learned from here).It had low freon issue before too.If is low on freon still will keep up cooling real nice between 11pm till 1pm?

 

I forgot to mention,the heat is always way up in my attic.I is 9:30 pm now and starting to cooling now.I checked the return air was 80 and exiting air(coil in it)was 70.thermostat was 81.ty

 

If you have had trouble with that AC unit before and had to have freon added it's possible that it is in need of more. In general I like to see a temperature drop of 15-20f but that is just a very crude guess and that number varies with the conditions like temperature and humdity.

At this point you can live with it or have an HVAC technician look at it. I'm sure everyone is calling to complain that their AC is not working so it may be a few days before they can get to you. For me it's $75 for a service call even if they don't fix anything and topping off freon usually brings it up to around $100. Your rates may be different but I'd just prepare for a $100 bill.

 

Thank you I call them.The service is 79 and freon 50 per pound.

 

At 80°F return-air & 70°F supply-air; that is only a 10°F temp-drop.
At around an indoor 50%RH the temp-drop ought to be around 18°F.

The Return-Air could have a leak & be sucking hot humid air from the attic or outdoors...or it could be low on R-22.

Check the air-temp off the outdoor condenser, list it here with outdoor temp.

 

Bur if it was sucking the hot air(return) ,it should do that in the ealy mornings too.After 10 am is 90 easy.I covered all the holes couple years ago in the attic,I will look at again in attic.tyvm

 

Sometimes it is difficult to find the Return-Air leaks.
Performance Data Collection – Best Time to collect data is late afternoon around +4:30 pm, when attic is HOT; also when outdoor temps are around 85°F to 95°F.

Not a DIY fix; all U need is a good air-temp probe thermometer (digital reading in tenths preferable) and a low cost 'Indoor Humidity Gauge' > ACU-RITE Digital only $8.94 at Walmart or over the Internet.
This form is for anyone to use & come on here to have us analyze if U need to call an HVAC Contractor.

1) Helpful: condenser 'Tonnage' & SEER Rating of Unit &/or model number:
FIRST; We need to know the 'Indoor' % of Relative Humidity______ %

2) TXV or, orifice metering device? _______. Only if U know; not critical…

3) Outdoor condenser’s discharge-air-temperature ___°F

Subtract Outdoor air temperature: _____°F

Outdoor Condenser Air-Temp-Split ___°F

4) Need the ‘Indoor’ percent of relative humidity - in the middle of the rooms or, at Return-Air inlet grilles ___

5)Subtract Indoor Supply-Air Temperature __°F
Return Air Temp ____°F Subtract Indoor Supply-Air Temperature ___°F
Indoor temperature-split = ___°F

Indoor temperature-split ___°F

“Reply with Quote” Fill the #numbers in where the blanks were. Easy Safe testing of your A/C or heat pump cooling performance for all the visitors to use:

First, make sure the return air filter is clean, and then you should get a digital probe thermometer that reads in tenths degrees, (though U can use any mercury thermometer) and a low cost percent relative 'humidity gauge 'to check the 'indoor' humidity level.

If you have an air conditioner that was manufactured between 1992 and 2005 it will 'probably be' a 10 or 12 SEER (though some were higher SEER even back then) R-22 refrigerant units.

When the temperature reaches around + 80 to 95°F outdoors and the indoor temperature is 80°F and the relative humidity indoors' is right around 50% RH the outdoor condenser temperature split should be around 20°F above the outdoor temperature.

If the indoor temperature is 75° and the relative humidity is 50% then the air discharge temp-split off the condenser should be around 17°F.

The indoor temperature split between the return-air at the supply air grille closest to the air handler should be a 18 to 20°F temperature drop with either an 80°F or 75°F indoor temperature. This is also the indoor split with the higher SEER units at 13 SEER or above.

If the indoor temperature split is too high may have very low airflow which needs to be brought up to its normal CFM Rate.

If the outdoor condenser split is too high your air handler may be drawing hot outdoor air into the return from the attic causing the high condenser discharge air temperature; or it has dirty coils or lack of ambient airflow through the coils, check for cottonwood if trees are in the area.

On the new air-conditioning systems & any systems at 13 SEER or higher, the outdoor condenser split is lower than it is on the 10 to 12 SEER units; the indoor temp-split is the same according to the humidity level.

New 13-SEER units have a 'condenser' temp-rise 'at above conditions' of close to 17°F; a 16 or 18-SEER usually around 9 or 10°F need model numbers for more definitive temp-numbers.

 

HVAC technician came and cheked it out and cleaned it too,he said it needs alittle freon but the unit is undersized.As soon as he put the freon and the exit nuber was 56 or 58.He said check the retun and exit #s if there less than 20 to 17 let them know.Let see when it gets real hot out there,right now it is a little cooler.

 

Are you talking about the tstat set point or the reading on the thermometer ?

Is this a new situation or has this done this in previous years ?

God bless
Wyr

 

Would be better if he had also found and fixed the leak .

By him telling you the system is undersize , that may be true or he may be setting you up to try to sell you a new system ?

How long has it been since refrigerant was added , the last time ?

How old is the system ?

God bless
Wyr

 

Indoor humidity has the biggest effect on indoor temp-split; not outdoor temp.
Indoor blower CFM has a much lesser effect on indoor temp-split or delta-T.

His comment that unit was undersized is unfounded, as he has no performance test proofs to make that claim. Due to his statements his competence is a bit suspect...a system may not be performing anywhere near its Rated capacity; it needs to be tested for "Delivered Performance."

 

I am going to get a ACU-RITE Digital and I let you know the #s.Indoor humidity is a issue in my house true.May be he was trying sell a 2.5,3 tons ac ,he told me the cost and everything.He did say that this can work for a few more years,just service it every year.

 

If for any reason the temperature reading does not agree with thermometers that you know are accurate, keep the receipt, and take it back. They have a guarantee...

They have an ACC-RUTE that is priced a little higher; if it has published accuracy data it might be worth the few dollars difference; there is no published accuracy data on the lowest priced one.

The just started stocking the new one.
The one I have is accurate but heard some may not be...