Understanding HVAC Control Boards for Air Systems

Diagnosing an HVAC control board is a tricky business. They can be extremely complex and even in the best of scenarios, trying to sort out resistors and capacitors can be a recipe for a headache, if not an actual solution. On the other hand, given how crucial these parts are, technicians must be able to diagnose, repair, and replace them and understand how to source the right boards to ensure customers’ systems can get back up and running.

Basics of HVAC Control Boards

At the very basic level, a control board simply receives an instruction from a thermostat or other control, including a user-operated switch, and translates that into an electrical voltage via a contactor or other means to turn on one or more components in an HVAC system. The steps for one of the simplest circuits might be for either a furnace or a forced-air cooling system:

1. The thermostat receives information from a sensor that the room is not at an adequate temperature.

2. The blower fan that will move air over the heating or cooling surface is told to switch on.

3. The control board instructs the furnace to ignite or the compressor to begin working along with a fan for the outdoor component.

4. When the thermostat receives information from the sensor that the proper temperature has been reached, it shuts down the whole system.

In this case, there are still multiple issues for the control board to address: when to time the blower fan operation, when to send an instruction to the furnace or outside unit, and so on. In all cases, these are handled with voltages sent to terminals, but control boards must be designed to interoperate with both the thermostat and the individual components.

More Features for Users, More Things to Go Wrong

As HVAC systems get more complex, the benefits for end-users increase. Integration with smart thermostats ensures that homes and offices are not needlessly heated and cooled. Using variable speed motors to control fans boosts integrated energy efficiency ratings, which are crucial for meeting new government regulations.

However, with each of these developments, the control boards become more complex. While a smart thermostat might send the same signals to turn on an air conditioning or furnace system, the control board may need to be specially designed for those instructions to be carried out in a dual-stage furnace, for example. Or, in the case of variable speed fans, the possibilities for control instructions skyrocket.

Trying to troubleshoot issues can become more complex, but only to an extent. After all, the components still only receive instructions through voltages to certain terminals. So, even a control damper might only have two terminals, one that has the motor turn clockwise, and the other turning it counterclockwise. It is still a matter of using a voltmeter to test different use cases.

Specialization in HVAC Control Boards

Due to the rising complexity of features that must be controlled electronically, many HVAC systems manufacturers have moved towards specialized boards that handle only specific portions of the system both for space reasons and to reduce the number of issues if a board manages to fail for any reason. Technicians now need to consider potential failures in:

1. Furnace controls

2. Air circulation and individual dampers

3. Blower fan controls

4. And other parts of the system

While there have been significant increases in the use of technology, at the end of the day the primary issue for technicians is ensuring that the wiring, voltages, and connections all match up if they need to source the right replacement HVAC control board as part of a maintenance or repair project.

Find the HVAC Control Boards You Need

As a leading distributor for the most trusted names in commercial HVAC and dehumidification, Affiliated Parts has the kits that you need to maximize the performance and efficiency of your systems or those of your clients. Shop our complete list of replacement HVAC control boards or contact us for more information.