How to Test a Gas Furnace Pressure Switch with a Multimeter

Test a Gas Furnace Pressure Switch with a Multimeter

This detailed guide teaches how to test a gas furnace pressure switch with a multimeter. Our step-by-step guide provides all the information you need to diagnose and repair issues with your furnace safely and effectively.

The role of pressure switches in a gas furnace is to control the appropriate amount of pressure that a draft inducer motor creates. If the pressure is not enough for the furnace, then the furnace is switched off by this pressure switch, and if the pressure is sufficient, it helps to run the furnace appropriately.

Different problems can alter the way this switch works, and it is also possible that the switch does not function properly, so in that case, it is important to test the gas furnace pressure switch. For testing, proper guidance is required, which you will get here.

How does a pressure switch work?How does a pressure switch work

The pressure switch responds to the process going on in a furnace. When a furnace works normally, the furnace’s heat exchanger produces exhaust fumes.

The draught inducer helps to take all these exhaust fumes outside from the flue pipe. At the same time, the combustion blower produces negative pressure, which is sensed by the pressure switch.

If all this function is normally going, the pressure switch will sense the negative pressure and remain off.

But if the exhaust fumes are somehow not getting out of the system, it will lower the amount of negative pressure, and when a proper amount of negative pressure is not sensed by the pressure switch, it will get on.

This normal functioning is required to run the furnace well, but if any problem occurs, the pressure switch will not respond that way, and we have to move forward toward testing the pressure switch.

A digital multimeter will be a good choice to test the pressure switch of a gas furnace, but first, we will check a few reasons that can damage the pressure switch and cause trouble in its normal functioning.

Reasons that can damage a pressure switch

The pressure switch of a gas furnace can get damaged because of the following reasons:

  • If some leakage occurs in the assemblies of the gas furnace, then it can damage the pressure switch.
  •  If something gets clogged in the drainage pipe, the exhaust fumes will not go out and can continually damage the pressure switch.
  •  If the Normal amount of electricity is not reaching the pressure switch
  •  If the draft inducer motor gets damaged, then it will not let the pressure switch do its work
  • If there is something stuck in the intake air pipe.
  • If the switch hose is not tight enough.

These are some reasons that can lead to the failure of the pressure switch of the gas furnace.

How to test a gas furnace pressure switch with a multimeter?

Tools required:

  • Digital Multimeter
  • Screwdriver

Below are a few (quick steps) to test a gas furnace pressure switch with a multimeter:

  • Turn off the electricity supply to the furnace.
  • Pull out the switch wires from the pressure switch terminals
  • Set the digital multimeter at resistance settings to test the pressure switch
  • Connect both the leads of the multimeter with switch terminals
  • Turn on the furnace to test the resulting readings through a multimeter
  • Look for the proper working of the furnace
  • A fine pressure switch will show 0 or close to zero readings on the multimeter. Any other reading on the multimeter will indicate it is faulty.

The step-by-step guide below to test a gas furnace pressure switch with a multimeter

Step 1: Turn off the electricity supply

When you test the pressure switch, make sure that no electricity is getting supplied to the switch; otherwise, you will get an electric shock, which can also damage the pressure switch, in contrast.

So it is compulsory to turn off the electricity supply before moving towards the next step of testing the furnace’s pressure switch.

Step 2: Pull out the switch wires

The next step of the testing procedure is to break the connection between the pressure switch and its wires. This step is important to ensure that the pressure switch has run out of electricity. You can pull out the switch wires by using the screwdriver. It will be a more protective way to perform this step.

Step 3: Set the digital multimeter

Now you are up to test the pressure switch of the gas furnace, so you have to take the digital multimeter and set it according to the requirement of the test.

For this test, you must turn the digital multimeter dial toward the resistance or continuity settings. Moreover, you have to do the more profound settings of selecting the single ohms rather than the mega ohms while testing the pressure switch.

Step 4: Connect the multimeter Leads

To test the pressure switch with the digital multimeter, it is important to make a connection between them, so you have to connect the leads of the digital multimeter with the terminals of the pressure switch.

You have to make the right connection while checking the digital multimeter’s positive and negative terminals regarding the black and red leads.

Step 5: Turn on the furnace

Now you have to start giving the furnace the electricity supply to check the furnace’s normal functioning while using the digital multimeter.

When the furnace gets the electricity, it will get on and will start performing its function, which influences the activation of the draft inducer motor, and the air will start getting out from the exhaust pipe. As a result, the vacuum will produce, which will turn off the switch.

Step 6: Look for the working of the furnace

Now you have to notice the working of the furnace. If you see any change in the furnace’s working, you have to consider it. Moreover, the other reading changes will be displayed on your digital multimeter, from which you will know whether your pressure switch is working normally.

Step 7: Check the results

This is the final step of this testing procedure in which you have to look up the readings your digital multimeter will display on its screen, from which you will decide whether you have to change the pressure switch off your furnace or it is working normally.

  • If your multimeter displays zero readings or is close to zero, your pressure switch works great.
  • Suppose you get any readings except zero, an infinity, or large readings on your digital multimeter. In that case, it means your pressure switch is not working properly, and you have to move toward changing your pressure switch.

Final verdict

The pressure switches act as the basic part, which reflects the normal functioning of the gas furnace, so if the gas furnace stops working properly, then the first thing to check in this condition is the pressure switch; sometimes, the pressure switch may not be the cause of the reason.

In that case, you can also check the other possibilities in this article. If you notice no proper reason for your furnace malfunctioning, you may have to have it checked by professionals, or you may have to change the motor this time rather than the pressure switch.

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