How to Troubleshoot a Central AC
Central ACs are fairly reliable and with proper maintenance, they should last 10-15 years. Some repairs are common but the vast majority of failures can be resolved easily and to identify the issue we need you to complete a few steps first before a technician is notified.
1. Check the batteries – Most often today the batteries in the thermostat need to be replaced and this will cause the AC to stop working properly. The first step is to change the batteries by removing the cover on the thermostat and replacing the AA batteries (Usually 2) and then attempting to run the AC normally. Even if the batteries are only a few months old you should attempt this step. All thermostats are different but the battery cover is usually a cover or small door on the front of the thermostat and sometimes on the side.
2. Check the breakers – There are always breakers in the main electrical panel for the exterior and for the interior units that are typically 40 to 60 amps. There will be one for each and they are double-pole (meaning double breakers), these are used for 220-volt appliances like AC, range, water heater). You will want to turn off all double pole breakers. Then go to the interior unit and find the breaker on or next to that and turn it off as well and the exterior unit must also have a disconnect or breaker where the power connects to the wall. Once all the breakers are turned off you can switch them back on in reverse order and attempt to use the AC normally.
3. Check the condensation lines – If the AC has a condensation pump or a condensation line that is blocked a float switch will prevent the exterior unit from working but the fan in the interior will still run normally. Check to see if this is the issue. If there is a condensation pump under the AC you may be that this is full of water. You can add water to see if the pump works and extracts the water. If not this may be the issue. If you have a switch at the bottom of the AC where the condensation line is located that switch may be broken or if the lone is clogged it will stop the AC from working. You can remove the switch and see if the AC restarts. If that is the case you can use a Wet/Dry vacuum to blow or suck the blockage from the line and the AC should start working.
4. Check the fans – With the AC working and the temperature set to something cooler than the current temperature check to see if one of the two fans is not running.
5. Check the filter and the coil – Is the filter recently changed? This should be done monthly and at least every 3 months. If the AC lacks airflow it will not work properly. You can also remove the filter and take a picture of the coil. If it is excessively dirty that may also restrict airflow and the AC will not cool properly.
6. Check copper lines – Check to see if the AC is running see if the small copper line is hot and the large copper time is cool. The large copper line that is usually wrapped in black foam is the return line. That should be cool as it returns to the compressor but not ice cold and certainly not frozen. The line from the compressor should be hot but not so hot. If these are both fairly close in temperature this is usually an indication the compressor is off (failed) and if the large line is frozen this is an indication of low refrigerant. You should not have any ice buildup on the interior or exterior of the Ac unit.
Please follow these steps and report the results. Then turn off the AC and set the fan to “off” as to not burn out any of the other components as they should not run constantly. You should never set the AC below68 degrees as this will not help cool and you probably are not actually seeking 68 degrees. If the AC cannot obtain 72 degrees setting a lower temperature will not help.