Last night I returned home from a month long vacation. Outside
temperature was about 90, and the humidity was very high. I turned the
a/c on and set the thermostat to 68 degrees. The a/c ran for at least
four hours, and the place felt much cooler, but the temperature was
still at least 74 degrees. I'm sure it felt cool because the humidity
was lower, but the temperature didn't fall.
The nice thing about this system is that it's quiet because the air
speed is normally low, but this means the unit runs longer, especially
for large changes to the thermostat setting.
Does the unit need servicing, like maybe a refrigerant charge? It's a
Rheem, newly installed in 2000. So far, never need any servicing.
Do you know what a thermometer is? Do you know how to use it properly?
What was the indoor air temperature before you started the AC?
What was the indoor temperature after the AC ran for 4 hours?
What is temperature of the air coming from your ducts?
Is the outdoor unit running?
What is the temperature of the air going into the outdoor unit?
What is the temperature of the air coming from the outdoor unit?
If the humidity is high as the op said, the ac will be unable to lower the
air temperature until after the humidity is reduced. So yes, it will take
longer to actually lower the air temperature, but you will ***feel*** coole
r as soon as the humidity is reduced.
On Thursday, July 3, 2014 9:42:06 PM UTC-4, email@example.com wrote:
e air temperature until after the humidity is reduced. So yes, it will tak
e longer to actually lower the air temperature, but you will ***feel*** coo
ler as soon as the humidity is reduced.
I agree with the essence of what you wrote, but the AC will in fact
be continually lowering the air temperature as the humidity is reduced.
It's just that it takes longer, because the humid air contains more heat.
If it was 90 degrees and your A/C brought your house to 74 degrees it
makes no sense that you stated "the temperature didn't fall".
Since your A/C only took 4 hours to drop the temperature 16 degrees it
looks like it's working...but it certainly would not hurt to have an
expert do the routine maintenance it undoubtedly needs.
On Thursday, July 3, 2014 8:47:54 AM UTC-4, philo wrote:
He said it was 90 *outside*. Totally lacking is what the temp inside
was. But if the AC was off and it was 90 outside, it must have been
plenty warm inside too. A better metric would be the temp of the air
coming out of the registers. It should be high teens difference, ballpark.
Years ago, I believe I read in the HVAC group that a unit can be fine
even if the drop is in the low teens. It depends on the dew point and
how much air is being blown through. I thought my unit was wimpy, but I
changed my mind after I got a meter that showed how far it was dropping
the dew point.
If the house has been sitting a month, the wood, paper, cotton, and wool
could keep keep the dew point up for many hours, meaning the temperature
won't drop as many degrees as it passes through the AC.
If you're trying to cool a house several degrees, a thermometer mounted
to something massive like a wall could read high for a long time. The
massive object can act as a heat sink, cooling slowly and keeping the
Years ago, my aunt brought my grandmother into a house that had been
sitting a couple of weeks. The central air conditioner was less than a
year old but didn't seem to be working. Eventually, it got the house
comfortable and has worked fine ever since.
Normally, I run my AC at night or in the morning and let the house coast
in the afternoon. Yesterday I ran it in the hottest part of the day and
discovered that it was using a lot more watts. I guess the compressor
really has to work harder when it's hotter.
I forgot to mention that the temperature of the air from the closest
ceiling register to the AC was 60F, same as immediately above the
To answer some of the other questions, the starting indoor temperature
was well below the outside temperature of 90. I hadn't anticipated the
slow cooling, so I didn't make the measurements asked for by others in
their responses. Yes, the outdoor unit is running, otherwise the
humidity would not have dropped so much. (No, I don't have before or
after humidity measurements.)
As I looked closer a few minutes ago, I see what may have been the
problem. During the winter, a portion of the return air is routed to the
humidifier via a separate duct, and thus bypasses the evaporator. I just
noticed that the damper in this duct was in the open Winter position,
instead of closed Summer position. I just changed it back to Summer.
Let's see what happens.
Later today I'll open the sheet metal and inspect the condenser.
Getting down to 68 may also be reaching the design limits of the unit
for a 90 degree day. Can I assume you have done that before?
If the changes you make above don't solve the problem, it may need
service. Usually a professional cleaning so the coils work at peak
efficiency and a check that you have enough refrigerant charge to work
properly. If a \minor loss, it would work OK, but not up to peak
cooling capacity. .
Seems like a waste of electricity, of fuel at the power plant, of the
world's resources, and of your money. You can get a setback
thermostat or at worst, it doesn't take that long for a place to cool
off or warm up, no matter how hot it's gotten. You can't let it
freeze and break the water pipes is the only limitation
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