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How To Find The HVAC Control Board

How Can You Tell If Your Control Board Is Faulty?

In every HVAC system, a control board is a crucial part. It’s also helpful to know where to look for it while trying to troubleshoot issues with it. Because of this, we looked into where HVAC control boards are and how to locate them. Here is what we discovered.

The air handler, where the thermostat wires enter the cooling system, is typically where the AC control board is located. Usually located in the blower chamber of a furnace, in front of the blower, behind the bottom access panel It ought should be instantly noticeable given the numerous cables that pass through and out of it.

How Does The Control Board Affect How Your HVAC Equipment Operates?

How Can You Tell If Your Control Board Is Faulty?

The control board for your HVAC system performs a number of tasks. These consist of:

Messages Other HVAC Components To Perform Their Function
One of its primary responsibilities is to analyse data from your furnace and thermostat sensors, draw conclusions from that data, and then communicate with other system components.

Your igniter might never receive instructions to operate if your control board isn’t functioning properly.

Supports Your Unit’s Safe Operation
But this part isn’t just a straightforward relay. Modern control boards are made by furnace manufacturers to track sensor input for red flags of issues. The safe running of your furnace is supported by this feature.

For instance, the control board may use data from the flame sensor to prevent your gas valve from being open if the igniter has failed.

Sends Error Codes To Notify You Of Potential Issues
Many control boards include the capacity to retain error codes, which can be used when a sensor produces incorrect data or when sensor data indicates a probable malfunction.

In these cases, it is frequently possible to identify the error code by contrasting a list of possible issues from the user manual with a flashing LED on the control board.

Replace Your Thermostats With Energy
It is startling to realise that the thermostats in your home are also powered by your control board. A transformer located inside the furnace’s housing transforms the 120V line electricity in your house to 24V. This voltage is then delivered to the control board, which distributes it to each thermostat in your house.

Which Symptoms Indicate A Faulty Control Board?

Given how important it is for your HVAC system to function properly, a damaged control board could lead to a number of issues. These indicators point to a failing HVAC control board:

  • You must pay attention if your board’s LED lights start to blink. If you notice anything weird with them, there might be a problem because they frequently blink in patterns. To accurately diagnose the problem, you should refer to your user’s manual, which lists error codes.
  • If you find that the temperature in your home is constantly fluctuating or if it abruptly gets excessively hot or cold, the control board may be faulty. Sometimes, the board fails to educate other system parts properly, which could lead to a total catastrophe.
  • Any changes to the usual course of events that your HVAC system is used to could be a sign of trouble. This is so because a typical HVAC system is designed to run in a certain order.
  • In essence, soldering stemmed plugs to the metal circuit. If done incorrectly, various complications could arise.
  • when the joints that fit the metal circuit have a gap. After it heats up and expands, the enlargement changes the form or generates gaps, which causes problems with the control board.
  • There is a jam in the electromagnetic switches. Usually, this issue is caused by either under or overvoltage. Due to damage from overheating, the switches stop functioning. On the other side, a low voltage could cause the relay’s contacts to open and close.
  • If you see any transistor damage. Unfortunately, too much heat and energy produced at starting could damage a number of components. Your control board could suffer significant damage as a result or work much more slowly.

How Can You Tell If Your Control Board Is Faulty?

How To Find The HVAC Control Board

You must first make sure that your control board is defective before you throw it away. You can do this by taking the following actions:

Part 1:

  1. Examine the port and contrast the light with the trouble codes mentioned in the manual or schematic for your furnace.
  2. Use your screwdriver to remove both access panels if necessary before moving on. The two access panels that are standard on furnaces are where the control panel and other inner furnace components are usually located. These might be secured in place by screws or a clasp.
  3. On the majority of furnaces, the door switch needs to be depressed in order for power to enter the furnace. As soon as the access panels are removed, this will become clear because they frequently act as a holdover for the door switch, keeping it in the down position. Use electrical tape to hold down this switch as you work.
  4. Verify that power is being provided to the control board. This is fairly easy to do if your control board has an indication light. The indication is an LED light that blinks when power is applied to the control board. You can move on to the following step if the board is powered.
  5. Locate the terminal strip for the furnace, which is normally close to the edge of the control board. You can see five wires on the terminal strip, each with a different colour and corresponding letters (R, W, Y, G, C). Using the “R” wire, you can see if low-voltage power is emanating from the terminal strip. With the leads of your metre, make contact with the “R” and “C” wires. You should once more see 24 volts.

Part 2:

After the fourth step on the first section, if the LED lights don’t flicker, which means it doesn’t receive any power, you can move on to the next steps:

  1. Discover the common wire on your transformer. Four wires total—two high voltage (often black and white) and two low voltage—are used in its wiring.
  2. To assist you in locating the line voltage, locate the wire that links the door switch to the control board. This line, which usually has the label “LINE” on the control panel, is what gives your furnace its 120 volts.
  3. Connect the metre leads to the high-voltage wires of the transformers. The transformer should be receiving 120 volts based on the reading on your metre.
  4. Utilizing the low-voltage cables, repeat the previous procedure. The transformer should be discharging 24 volts, which is what your metre should be reading. The transformer is probably broken and the cause of the problem when it accepts 120 volts but does not output 24 volts.
  5. The two low voltage lines should be traced back to a Molex connector on your control board. If you place your meter’s leads into the Molex plug sockets where the low-voltage wires are linked, you should once more see 24 volts shown on your metre.
  6. Re-do step 5 from the first section of this guide.

If you accomplished all the steps above and your transformer, Molex plug, and thermostat terminal strip are all receiving power from your line voltage, your furnace control board is operating effectively.

What Is The Price Of Repairing An HVAC Control Board?

How Can You Tell If Your Control Board Is Faulty?

The normal price range for replacement furnace control boards is $300 to $650.

  • A furnace motherboard or circuit board can cost anything from $50 and $300 for only the component.
  • Its replacement will cost between $250 and $350 in labour.
  • HVAC professionals charge $75 to $150 per hour for furnace repairs.

In contrast, repairing a control board for an air conditioner that is not under warranty can cost anywhere between $150 and $700; if it is, labour expenses can be somewhere between $100 and $300.

The cost of an AC control board alone might vary from $50 to $400 depending on the brand, kind, and model.

How Long Does An HVAC Control Board Have To Function?

A circuit board normally lasts 10 to 15 years, depending on the furnace’s condition, operation, and level of maintenance. Circuit boards last longer as a result of yearly furnace inspections and performance-enhancing filter cleanings.

A similar lifespan of 15 years or more is expected for an AC circuit board, which lasts as long as the HVAC system itself.


The HVAC control board is simple to locate. It can be found in the air handler unit or blower chamber of your furnace. Simply open the front panel of your unit and remove it to find it.

How Can You Tell If Your Control Board Is Faulty?

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Written by HVAC Contributor

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