What To Do If There's No Power to the HVAC Control Board

The AC unit, air handler, and furnace are familiar parts of your HVAC system. However, the control board isn’t something you often interact with. If it’s not working, it can’t command any part of your heating or cooling system to operate correctly. We’ll explain what it is, how it works, and what to do if there’s no power to the HVAC control board.

What’s an HVAC Control Board?

The control board is essentially the system’s command center. Input from the thermostat is received by the board, which then relays the appropriate commands to your furnace or air conditioner. A furnace circuit board regulates the ignition, gas valves, flame sensor, blower motor, and other components. A defrost control board works similarly, except it monitors for the buildup of ice and triggers the defrost function when it’s needed.

How to Check the Control Board

First, you’ll need your furnace’s manual, which should show the location and setup of the control board. Before starting, you’ll also need a screwdriver, electrical tape, and a voltage meter. Proceed with the following steps if there’s no power to the HVAC control board:

• Remove the Access Panel: Open the panel, using electrical tape to hold it open. Locate the control board, which is often at the bottom near the blower.
• Check for Damage: If there’s physical damage such as faulty wires or burn marks on the board, it’ll have to be replaced.
• Use Your Senses: Do you hear buzzing sounds? Are there burning or other strange odors? If so, call a professional right away.
• Check the Diagnostics: Look at the diagnostic light on the control board. If it’s not on, the board isn’t powered; if the light is blinking, count the blinks and refer to the manual to determine the problem.
• Test the Power: Check for a door switch on your furnace or HVAC unit; tape it down to prevent any electrical accidents. Using a voltage meter, test the common wire from the transformer to the board. The meter should read 120 volts AC. If not, the board should be replaced.
• Check the Terminals: One last step before replacing the control board is to test the thermostat terminals. After turning the system off, reconnect wires to test each terminal, turning the unit on and off in between tests. With the R and G terminals connected, the blower should activate; connecting the R and W terminals should trigger the heater while connecting the R and Y terminals should turn on the AC. These responses are assuming the control board is powered and functioning.

How Do I Know There’s a Control Board Problem?

If the control board isn’t working, there may be issues with temperature regulation. The symptoms are often similar to those associated with other problems, such as blower fan, power, or filter issues. If your HVAC has warning lights or diagnostic codes, you might see a notification of an unpowered or failing control board. However, the system may not work at all if the control board isn’t powered. 

Why Does an HVAC Control Board Fail?

The control board should last the life of your HVAC system. But high temperatures, numerous heating and cooling cycles, or wiring issues can wear it out. A single faulty transistor or relay on the board can result in a malfunction. Sometimes a faulty transformer or fuse is the cause; a technician can provide replacement components to fix the problem. If the board is damaged, usually the only option is to replace it, which requires a professional to handle wiring and installation work.

Call NexGen If There’s No Power to the HVAC Control Board

Customers throughout Southern California rely on NexGen for all types of heating and AC repair. If you have temperature control, airflow, or power problem or need an HVAC control board replaced, our licensed technicians will get your system running again in no time. They are fully licensed and insured. You can reach us 24/7 by calling (833) 729-9735.