A furnace control board is essentially the computer, or the brain, in a furnace. It operates the key functions in the order that they are supposed to happen and controls everything from turning on the gas to shutting down the fan after your home has reached your desired temperature. While it is a very essential piece to your furnace it is common for control boards to be replaced.
TYPES OF CONTROL BOARDS
There are two types of control boards for gas furnaces. The first is a simple ignition control board module, which is more common in older, less efficient models. It controls the gas valve, the igniter and the flame sensing circuit. These older units will have a fan control board along with the simple ignition control board.
The more common control board, at least in newer units, is the integrated furnace control board. This controls the same things as the simple ignition control board but it controls the furnace blower as well. Ultimately it is the simple ignition control board and the fan control board in one.
To understand whether or not your control board is operating correctly, it is first imperative that you understand the step-by-step sequence of your furnace, which should be like this:
- The thermostat is set and calls for heat.
- The induced draft motor turns on.
- The pressure switch senses a drop in pressure and closes to complete a circuit.
- The control board sends a signal to the hot surface igniter and the igniter lights up.
- Then a few seconds later the gas valve clicks and releases gas to the burners.
- The burners ignite in sequence.
- The flame sensor senses the flame and allows the gas to continue to flow, heating up the furnace.
- The blower motor turns on and moves air through the furnace to keep it from overheating.
- The limit and rollout switches remain closed and continue to monitor the airflow.
- Once the thermostat is satisfied, the control board shuts off the gas.
The control board can also help you diagnose a problem with your furnace. Most control boards have LED lights that flash to indicate a problem. The different flashes serve as codes. Follow the chart on your control board to decipher what the flashing code means. The code might tell you that you need a new control board.
Control boards also have lights to let you know that it is on and functioning correctly. If this light is not on, then the control board can be reset by turning off the furnace power and restarting it. However, this is not normal; a control board should not have to be reset.
CONTROL BOARD REPLACEMENT
If you find that you need a new control board, HVACPartsShop.com can help you find the correct replacement part. Use our furnace model drop list to select the correct control board using your furnace model number. You can also use the manufacturer’s part number to find the correct part. If you are still having problems figuring out which control board is right for your model you can use our online chat feature to chat with a certified technician or you can call us at 1-866-215-3831.
When you begin the replacement, please first make sure that the power to the furnace is off. Before removing the wires make sure that you have marked them so that you know which connection they go to. Then remove the wires, screws or clips and the old board.
Attach the new board and carefully reconnect the wires to the proper terminals. Then restore the unit and run it through a complete cycle, verifying that is follows each step of the sequence.
The main function of a capacitor in an HVAC system is to provide the additional torque needed to get a unit running and the electricity needed to keep it running. There are different types of capacitors and you will find different types in different HVAC systems. As in the video, let’s begin by explaining start capacitors:
Start capacitors can be seen in outdoor units such as air conditioners and heat pumps, and are in addition to a dual run capacitor, which we will cover later. Generally only high-end factory models come with a start capacitor, but start capacitors or super boost capacitors can be installed in older or smaller units in order to increase torque and quicken start up.
The purpose of a start capacitor is to get the compressor up and running as fast as possible. As the compressor begins running, the potential relay will disconnect the capacitor from the electrical circuit. The two parts go hand-in-hand and it is a good idea to purchase them together.
A super boost capacitor is another type of start capacitor that has a potential relay built into it. This capacitor is very easy to install. It has two interchangeable wires – one that connects to the common terminal and one that connects to the HERM terminal. It can easily be stacked next to the run capacitor in your unit. If you have any additional questions about installation, please feel free to contact us. We are here to help.
We can also help identify the size and ratings of your capacitor so that you can replace it correctly. It is common for the label to become rusty and hard to read. As long as you know your unit’s model and serial numbers we can find the right capacitor.
Dual Run Capacitor
Dual run capacitors are also found on outdoor AC units and heat pumps and come in a variety of shapes and sizes. They are able to support two motors – the compressor motor and the fan motor. The dual run capacitor runs continuously while your unit is running. It has three terminals: HERM connects to the compressor, fan connects to the fan motor and common connects to the contactor. It is imperative to connect each wire to the appropriate terminal.
Again, it is important to read your data sticker in order to purchase the correct size of capacitor. The data that you should be looking for are the microfarads and the VAC, or voltage amp current. The capacitor in the video shows a capacitor with 45 + 10 microfarads. This means that 45 microfarads will go to the compressor and 10 microfarads will go to the fan motor. The new capacitor that you purchase must have the same amount of microfarads. VAC, however, is slightly different. If you are replacing a 370 VAC, you may replace it with a 440 VAC, but you cannot replace a 440 VAC with a 370 VAC.
Single Run Capacitor
Single run capacitors are generally used in furnaces. They have two terminals, HERM and common. The two wires that come from the furnace’s blower motor can connect to either terminal.
Over time, single run capacitors can get weak and you will begin having problems keeping your furnace running. If your fan motor is making a humming sound, this is a sign that you need a new capacitor. Note, it is dangerous to use your hand to give your blower motor a push. Please refrain from doing so.
Two additional safety tips for replacing your capacitor are:
- Make sure the power to the unit is off, both at the unit and at the circuit breaker.
- Deactivate the electrical charge, by using an insulated screwdriver and touching each terminal. It is also a good idea to wear insulated gloves.
Thank you for watching (and reading) our video. Until next time, stay warm!