All modern HVAC systems use a control board for numerous purposes. These boards provide low-voltage power to your thermostats, relay calls for heating and cooling to the furnace and air conditioner, and perform other functions that allow your system to operate safely. Most homes will have one board shared between the furnace and AC, but you'll have one even if your home only has an air conditioner.

Since your control board serves many functions, diagnosing problems with it isn't always easy. A faulty board can produce a range of unusual or hard-to-pinpoint symptoms. While the complexity of an AC control board means that you'll always want a professional to handle these issues, this guide will go over three symptoms you might experience if yours is failing.

1. Extremely Unusual Thermostat Behavior

Thermostats are simple devices. Even if you have a smart thermostat, the core of what's happening behind the scenes is the same: the thermostat calls for heating or cooling based on the ambient temperature and its setpoint. When you have your thermostat in cooling mode in summer, it will call for cooling when the temperature goes above the current setpoint.

One potential clue that your control board is in trouble and that you're not experiencing some other failure is strange thermostat behavior. For example, your furnace may come on at the same time as your air conditioner, or your air conditioning compressor may turn on at seemingly random times. While these aren't surefire signals of a control board problem, they're a clue that something is wrong.

2. Error Codes

Most modern HVAC control boards include a display to help technicians troubleshoot problems. This display may be as simple as a single LED light or a more complex numeric LED display. In either case, the control board will display error codes when it thinks something is wrong. These codes are usually cryptic and may just be a series of flashing lights, so you'll need to cross-reference with your AC manual.

Most systems will have a specific code (possibly just a single, steady red light) to indicate a control board issue or failure. This code doesn't necessarily condemn your control board, and you will need a technician to attempt further diagnostics. Still, it's another solid indicator that your control board may be at the root of your AC problems.

3. Temperature Inconsistencies

Remember that your air conditioner should only run while the ambient temperature is above your setpoint. While other issues can cause your AC to struggle to keep up, it generally shouldn't keep running well below your setpoint temperature. If your home's temperature seems to vary up and down, no matter how you set your thermostats, you may have a control board issue.

As with other symptoms, there are other potential causes for this problem. For example, a faulty thermostat may also be to blame. An HVAC technician can check these other components to rule out simpler causes before replacing your system's control board.

For more information about air conditioning repair, contact a local company.