House does not cool below 76

Problems related to residential installations.

House does not cool below 76

Postby Bulldog455 » Wed Jul 15, 2015 10:25 am

So Im new to the Hvac world, I recently bought a new house its a mid century home with a slightly sloped roof, 3 bedroom 1590 sq feet. I had the home inspected unfortunately it was cold out when I bought the house and we could not check the a/c. my past experience with central air you could set the thermostat at 72 and the unit would cycle as needed...
With my new home, I can not get the a/c to cool the house more then 76 degrees... the unit just runs consistently. Like today for example it was 91degrees outside.. when I got home at 4pm the temp inside was 80 degrees.. I turned the system on and set thermostat at 78.. it is now 830pm and the unit just now kicked off at 78 degrees...

here are the details of what I have done and what I know....
had a/c guy come out and check the Freon levels... They are fine!
changed thermostat to a Honeywell
checked the temp at the unit... 52 degrees
checked the temp at the register... 54 degrees (closes to unit}
check the temp at the return... 72 degrees (closes to unit)
changed filters
cleaned outside unit
removed blower and motor / cleaned
it just does not seem to be blowing very hard inside / in my past home the air blew out a lot harder then it does here
checked air ducts in crawl space to insure nothing came unhooked... they looked good.. have insulation around the pipes ect...
I have 2 registers in every room except kitchen and living room I have 3
I have 2 returns in the dinning room and 2 in the hallway
I have 6" air duct coming off the main duct
the house sits on a crawl space

I have a goodman a/c unit 2.5 ton was new in 2012
I have a payne furnace rate for 95000 btu with a 80% efficiency so should be putting out around 76000 btu's
the furnace itself is 14 years old... does it need replaced?
one more thing the furnace is in the 2 car garage does this make a difference?

Im really at a loss.. any help would be great...

Thanks if you need additional info please ask and I will get it for you
Bulldog455Minimal - - Tue Jul 14, 2015 - pm
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- House does not cool below 76

Postby Freon » Wed Jul 15, 2015 3:37 pm

The one place you need to check is the evaporator coil in the furnace. It can easily become clogged if the previous owners were negligent about filters. Not knowing the cfm of the blower or the ducting it's hard to say why the air flow feels weak (low velocity). Usually returns are the choke point.

Now I will add the following. Having your AC run constantly is a good thing for 2 reasons. First it is the most energy efficient mode of operation. Second, it is less wear and tear on the system.

Now for a little thermodynamics. All objects (mass) in your house are like batteries when it comes to heat energy. They store the heat. The term is heat capacity and every object has it. When you leave your house and the temperature rises, all the objects begin to store heat energy... tables, chairs, Sheetrock walls and more. When you come home, your house is charged with heat energy... many thousands of BTUs. So your AC has to remove (discharge) the stored heat energy. It is no wonder it takes hours for the house temperature to drop.

A bigger AC system would do the job faster but would be more inefficient because it would cycle on and off. I suggest setting the thermostat to start the AC an hour or 2 before you get home.
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- House does not cool below 76

Postby Bulldog455 » Wed Jul 15, 2015 6:14 pm

Freon,
Thanks for the information, I did pull the cover off the front of the indoor unit and the coils look very clean..

I will try to set the thermo down 2 hours before I get home or maybe just let it run and see what the house feels like tom when I get home
just one more question.. is there an optimum temp it should be set at? and A good working system should cool the house down to what temp? ( inow this depend on outside temp was just wondering as a rule of thumb how cold an a/c would get a house

will update soon... once again Thanks
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- House does not cool below 76

Postby LennoxHVAC » Thu Jul 16, 2015 10:10 am

" I can not get the a/c to cool the house more then 76 degrees... the unit just runs consistently. Like today for example it was 91degrees outside.. when I got home at 4pm the temp inside was 80 degrees.. I turned the system on and set thermostat at 78.. it is now 830pm and the unit just now kicked off at 78 degrees... "

It appears to be doing its job.
However, are you expecting cooler temps than 76º-F?
Do you have duct work in the crawl?
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- House does not cool below 76

Postby Freon » Fri Jul 17, 2015 7:34 pm

Get a temperature and humidity gauge. Many cigar stores sell them. Comfort is a combination of temperature and relative humidity. I cold damp (high humidity) house is cold but uncomfortable (clammy). The higher the temperature the less it will cost you. But less AC running time (high temp house saving $$) means higher humidity. It's a balancing act that only you can determine when it's balanced. Your system seems adequate. Longer run times for the AC means less humidity and that should be more comfortable.
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