Does my air conditioner need service

[Rebel1]

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.

Thanks,

Ray

[Stormin Mormon]

Probably needs the condenser professionally cleaned. And check the freon level. And it most likely needed service after four or so years. 14 is way too long.

[V Ague]

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?

[philoÂÂ]

X

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.

[trader_4]

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.

[Rebel1]

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 evaporator.

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.

Thanks everybody.

R1

[Tony Hwang]

Hi, I never shut off system when we are away. Just set it to run at higher(cooling), lower(heating) settings on hold. When we return, back to normal settings for quick recovery.

[Ed Pawlowski]

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. .

[bob haller]

a major cause of AC troubles is a dirty air filter, when was yours last changed?

[micky]

AFAIK the only reason humidity drops is that the air is cooled.

There is no magic way to remove humidity without cooling the air, afaik.

[micky]

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

[Tony Hwang]

Yes, Thermostat is of course programmable. When away it is set at 14C heating, 25C cooling. I don't want to have our 102 YO grand piano get busted. Also houseful of plants. Normal setting is 20C and 23.5C. Next 4 years 8.9cents/KWh, $3.75/GigaJoule NG. After 4 years I have to renegotiate the rate. System is hi efficiency, 96%, 18 SEER always kept in tip top shape.

[J Burns]

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 thermometer warm.

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.

[Pico Rico]

you sound a bit hot under the collar.

[makolber]

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.

Mark

[micky]

Did anyone mention cleaing the furnace filter? Or replacing replaceable ones.

[Rebel1]

I don't know. Never set it to 68; that would be too cool for me.

[Stormin Mormon]

Open bypass makes it more likely to freeze evaporator. I'm guessing the condenser needs cleaning.

[trader_4]

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.

[V Ague]

Warm moist air is less dense.