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Heating & Air Conditioning

New central air unit not cooling

11 years ago

A couple months ago I had me central air and heat replaced. It was cold outside and we have been using the heater, which worked great! Now we are having hot weather so we switched the thermostat from heat to cool, and changed the temp to 78 degrees. When it gets hot outside the fan comes on, and the thermostat indicates the unit is cooling, but there is not cool air coming out of the vents and the unit runs for hours without stopping. The temperature on the thermostat never gets to 78 so it doesn't shut off. And if I come into the house from outside, I notice its humid and we sweat when we are just sitting watching tv! This has happened for about the 5 days we've tried to use it, and we end up just turning it off and opening windows. I went outside to the unit and felt the cables coming out of the unit and all are warm except one narrow copper tube is cool. Does anyone know what I can try to make it work right? Or does the installer need to come to my home and check it?

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Comments (3)

ryanhughes
11 years ago
The installer will need to come back out and properly charge the system and also ensure there are no leaks in the system connections. If it was cold outside when they installed the air conditioner they would not have been able to charge it accurately. Now is the time to come out and do so.

This post was edited by ryanhughes on Sat, May 4, 13 at 10:50
Bob1981
11 years ago
A more common problem could be that the Thermostat is wired incorrectly or one of the 18gauge wires feeding into the back of the thermostat came loose during installation. Just a thought...

This post was edited by Bob1981 on Tue, May 7, 13 at 19:32
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To answer your question about humidity, there is a significant amount of heat energy that is stored/released when something changes state. So, for example, when freon changes from a liquid to a vapor, it absorbs a large quantity of BTU's and gives them up when it changes back in the condenser. Likewise, water does the same thing. You can bring a pot of water to boil and the water will reach 212 at sea level. You can then apply additional BTU's but the water never changes temperature. The heat is being absorbed by the water as it changes state to a vapor. The reverse happens on your evaporator coil. You have to remove some of the moisture in the air - and the heat energy that is stored in that water vapor-- before it can begin to cool the air much. Most residential systems are designed "under-sized" to run longer so that they remove the humidity rather than blasting cold air and shutting off. Otherwise you can have a house that is cool, but clammy and humid.
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rickymartin85
11 years ago
If you believe that the air is moving sufficiently inside let's check the outside unit.

1. First feel the air coming out of the unit. You should feel heat being removed from the house.

2. Next look at the 2 freon lines - there will be a big one and a little one. The little one may be very hot so be careful. The big one is the low pressure side and on normal conditions where the pipe is exposed should be cold a sweaty.
From this big line you can tell alot.(you will have to find a place where the insulation is off or right where it goes into the outside unit)

3. If it is frosted up then go to 4 if not go to 5.

4. This could be due to either insufficient air flow across the coils of the inside unit or low freon which will cause the coil to start freezing.
If there is frost, cut the unit off at the thermostat by switching the heat/cool switch to off and turn the fan switch from auto to on. This will cause the fan to continue running and turn off the compressor outside. Leave it this way for a minimum of 30 minutes. See if you notice the air flow to improve coming out of the vents. While it is off you can check your air filters and make sure they are clean. Replace if necessary. Later turn the A/C thermostat back to cool. Notice if it cools better and monitor the big line. If after about five minutes the line is cool to cold then the freon level may be OK and you should feel hot air coming out of the unit. If it is only barely cool or not cool the unit is probably low on freon.

5. If the big line is not cool and the little line is not warm then either you are very low on freon or your compressor isn't running. Either way you will need to get an AC repairman for repairs.

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