Central Air Conditioner not cooling well


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Old 05-06-14, 01:54 PM
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Central Air Conditioner not cooling well

I live in Georgia. I have a 4 ton Air Conditioner. The heater works fine. It is 15 years old. It has always cooled very well but last year I started having problems. The air condtioner stays on from the morning until night. It just doesn't cool the house like it use to. I set the thermostat for 78 degrees. During the late afternoon it will be at between 80-85 in the house. At night it will finally cool down to 78. This happens even if it is only 90 degrees outside!

So last year I called a repair man out. He said my air conditioner unit was fine just dirty. So he cleaned it and replaced the thermostat. That didn't work. We lived being miserable all last summer.

So a couple of weeks ago I called a different repair man out. He said the same thing as the first guy! So he cleaned it. That did not work! He even took the blower out and cleaned it.

Now I am sitting here with the thermostat set at 78 and it is 81 in the house and only 89 degrees outside. The air just doesn't feel real cold coming out of the vents.

I put a thermometer in the vent to see what the temperature was. It read 69 degrees. The humidity in the house is 53% which is crazy because the outdoor humidity is 20%! It feels cooler outside than it does inside.

Also the air conditioner outside used to blow out hot hot air. Now its just luke warm. About as warm as the temperature outside.

I don't know what else to do. Please help! Any help or ideas is Greatly Appreciated....

Tina
 
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Old 05-06-14, 04:48 PM
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From what you say, you are getting a 12* temperature drop at the furnace. That is a little low. Do you know if they added refrigerant?
 
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Old 05-06-14, 05:26 PM
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Is your system in the attic?

You have to check the split across the furnace itself (in the attic) rather at the vents. A major problem (like a disconnected return duct) could be throwing off your readings. A/cs are much more sensitive to duct problems than furnaces, so if there's a duct problem, it may only show up in the summer.

Is the suction line (large insulated) cold? Did any of the techs put gauges on the system or take any other measurements?

At 78F, 53% return, your supply temp should be 55F, so there is a problem. (according to this: Charts - Efficient Indoor Comfort, wetbulb temp calculated using Psychrometric Calculations)
 
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Old 05-06-14, 05:48 PM
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No refridgerant was added either time. The system all check out good. My ducts are under the house. It is a doublewide mobile home on a permanent foundation. Built in 1999. I have had 13 years with no problems besides general maintenance. It started last summer. Under the house it is always cool. The permanent foundation is made of block and stucco.

I took the reading of 69 degrees in the vent closest to the blower. Which is only about 4 feet away. The suction line is cold and has condensation on it. The little line is luke warm. Not hot.. Just warm.

Oh the home is about 1800 square feet. Thanks for the help

Edited: I forgot to say, the techs only mentioned the coolant was fine. They tested other thing for amps and checking heater coils? and a few other things but all was good. They both said my system is running good. But there is something wrong. On top of being hot and miserable last summer, with my system running all the time, my electricity went up at least $60 a month. Maybe my compressor is going out?

I will have my husband check the ducts this weekend. The techs didn't do that. You can't see the ducts due to insulation and the plastic netting. Would it be moving if there was a leak in the ducts and the unit was on?
 

Last edited by Mystary; 05-06-14 at 06:11 PM.
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Old 05-06-14, 06:03 PM
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I have doubts about the two Techs that came out. I would check out the duct work. At this point I wouldn't think the compressor is bad.
 
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Old 05-06-14, 06:12 PM
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Tina, how does the volume of air feel coming out of the vents? Does it feel as strong as you remember? My previous house had a similar problem. The system was about 15 years old, and worked fine for years. Then, we had a pretty hot summer and we realized that the house just wasn't being cooled properly. 2 techs both said the system was ok, other than needing to be cleaned (and the first one sold us a new thermostat lol). I noticed that the air was cold coming directly out of the vents, but that the volume was low. Taking the air filter out didn't help any. Turned out the evaporator core was clogged with 15 years of dust that had gotten by the filter and finally built up enough to cause a restriction. Made an effort to clean it and it made a huge difference. Alas, we ended up replacing the whole system soon after, because there was no way to thoroughly clean the coil without removing the whole thing, and we still would have had a clean, but old, outdated system. Just a thought for you. Good luck.
 
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Old 05-07-14, 02:06 PM
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Also the air conditioner outside used to blow out hot, hot air. Now its just luke warm. About as warm as the temperature outside.
The lack of heat coming off the condenser coil indicates that the indoor evaporator is NOT absorbing but very little heat.

They probably didn't do much of a job cleaning it; a dirty coil/fins will also cause low airflow.

Your system is removing very little heat from the air in your home.

It is very important to have clean coils/fins & adequate airflow so the indoor coil can absorb the sensible heat & the latent heat of condensation.

The Edit: If room return air is 53% & room temp is 81F the air coming off the condenser should be close to 20F above the outdoor temp.
 

Last edited by HVAC RETIRED; 05-07-14 at 03:09 PM.
 

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