The control board for your AC's fan and compressor is an important component. If it fails, the entire system fails. 

1. Frequent Cycling

One of the most common causes of control failure is stress on the system from frequent cycling. Cycling issues can occur when a unit isn't sized correctly for the home, so it must pop on and off more frequently to maintain the set temperature. Problems with air flow through the unit and overheating can also lead to frequent cycling. Your repair tech must address the causes for the cycling issues and replace or repair the failed fan and compressor controls. 

2. Corrosion

Moisture and dirt can get into the control system, and both mean trouble. Moisture leads to corrosion, which can lead to poor electrical contact at the terminals within the control board. Dirt and dust are similar. Cleaning out the control board and fixing loose connections should solve the issues, but sometimes rewiring or even replacement may be necessary.

3. Sensor Failure

The thermostat sensor is behind the thermostat control panel in the house. This sensor relays the information on when to start and stop to the control board for the fan and compressor. If the thermostat sensor is malfunctioning, then it will send faulty information that can lead to an overworked control board or even a short in the electrical system. Both the sensor and any damage to the control board must be fixed.

4. Malfunctioning Capacitor

There are multiple capacitors in an AC unit. These devices store up power so that they can provide the energy needed to activate the various moving parts in your unit. The capacitor that controls the compressor and fan does a lot work, so it is not uncommon for these to fail long before it is time to replace the entire AC unit, which means the control board won't receive the power it needs. The good news is that replacing a malfunctioning compressor capacitor is a quick and cost-efficient repair.

5. Fan Blower Stress

Control failure can be a result of an overworked fan blower motor. The most likely culprit here is a dirty, poorly lubricated motor and fan assembly. Preventative maintenance, including cleaning and lubricating the assembly, is the best option. Otherwise, your AC tech may need to rebuild or even replace the blower motor as well as repair the control board.

Contact an air conditioning unit repair service if you suspect control failure in your AC.