On Sun, 08 Jul 2012 23:05:17 -0400, Ed Pawlowski <
e...@snet.net> wrote:
>On 8 Jul 2012 21:06:19 GMT, notbob <
not...@nothome.com> wrote:
>
>>On 2012-07-08, Brooklyn1 <Gravesend1> wrote:
>>
>>> If central A/C is set at 60º and it's still can't cool then there is
>>> something wrong with the unit, could be out of freon.
>>
>>Or jes too small a unit. If it takes 3500 btu's to lower a house/room
>>1 deg and the unit is only 2500 btu's, ain't never gonna get there.
>>
>>I would think a central air unit would be large enough, but if it was
>>marginal to begin with and weather heat patterns increase higher than
>>originally calculated, may be time to upgrade.
>
>Most units are designed for a 20 to 25 degree temperature drop from
>outside temperature. At 104 outside, he is probably seeing the
>maximum design capability of the system.
I think your rationale is reversed. Most A/C units will stop cooling
when outside temperature drops past a certain point, usually 60ºF
(even window units), the blower will run but the compressor motor
won't. But regardless how high outside temperature the unit will
continue cooling, or at least try to, but often when folks don't have
their units serviced yearly problems result. I maintain a service
contract on my central A/C, the tech makes an appointment to perform
servicing after mid may, so as to ensure that the outside temperature
is above 60ºF or the unit won't operate and then he can't perform the
necessary tests. It's very rare that a central air system is
undersized, most are over sized and that is not a good thing, because
if the unit's BTU rating is too high it will cool at too high a rate
so then it will stop cooling well before it pulled out enough
humidity... the house will be cold and clammy, dank... and that
produces condensation inside the walls so that mold grows. The
function of A/C is threefold, cooling, dehumidifying and filtration, a
properly sized unit will perfom all three functions. Even if a house
is low on insulation a properly functioning A/C unit will still cool
the space to the selected temperature, only it will take longer to
reach that temperature and will cost more to maintain that
temperature. When the unit cannot achieve the set temperature,
assuming there isn't a window open, it's almost always in need of
coolant, or the high setting of the blower motor is not functioning...
in periods of brownouts it's common for that particular circuit's
breaker to burn out. Most units have a two speed blower motor, high
speed kicks in when the compressor motor comes on, low speed runs
constantly to maintain, circulate and filter. People who don't have
their A/C serviced regularly can go for years with insufficient
coolant and without the high speed blower operating, can cost them a
fortune to cool their house, it won't cool, dehumidify, and circulate
efficiently, nor will it reach a comfortable temperature on warmer
days no matter how low the thermostat setting.