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Why won't our air conditioner cool our house?

We just purchased a 1 ton central air conditioner. We have a 985 sq. ft. bungalow. The problem is the system continuously runs when the outside temperature is 83 and the desired temperature in the house is 74. We like the house a little cooler at around 72 but the system, for some reason, is unable to achieve this. We replace the air filter every month. The air is coming out of the vents isn't cold -- more like cool. I suspect something is not right with the new unit. We replaced a 20 year old Keeprite unit. It never ran for long periods nor had trouble cooling the house to 70. The installer has used every excuse why the unit runs for the long periods but it just doesn't make sense.

Building Supplies , HVAC
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1 Answer from this member:
Manage My Life
As a rough rule of thumb, homes in Northern United States and Southern Canada require a ton of air conditioning for every 700 to 1000 sq. ft. Therefore 1 tons sounds reasonable. The risk in oversizing a unit is an uncomfortable climate. Oversized air conditioners come on for short periods of time and drop the air temperature quickly. Because of their large capacity, they satisfy the thermostat before the system has a chance to do much dehumidification. This can lead to a cold clammy environment inside the house.

However, the unit should be able to maintain at least a 15 degree temperature differential between indoors and outdoors. If the system is adequately sized and is working properly, the air temperature entering the evaporator coil will be whatever the room temperature is. Let's say it's 75F. The air coming off the coil should be 15F to 20F cooler. If the inlet temperature is 75F, the air coming off should be 55F to 60F. This can be measured with a thermometer with a sharp probe that is pushed into a joint or hole in the supply plenum immediately downstream of (or after) the evaporator coil.
by Manage My Life
April 26th, 2007
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