Pressure Switch Troubleshooting Tips

I'm often asked what is the best way to troubleshoot a Pressure Switch? I use a Fieldpiece SDMN5 Dual Port Manometer. Some may prefer a Magnahelic Guage as it reacts a little quicker. Either is a good choice and provides a "window" into the system.

It's important to understand that all pressure switches are not applied in the same manner. What I mean is this; some are sensing only one side of the switch (as in an 80% furnace). Others are differential switches which reference two points in the furnace (burner box and inducer or collector box side). And yet 2 Stage furnaces have Two switches. Each have a different make/break relevant to the High or Low speed on the Inducer. Knowing the specific application will help in understanding what to expect.

The SDMN5 Dual Port Manometer will read Two sides of a pressure switch or Two pressure switches at once. However, be careful not to interpret the bottom reading as the Second switch reading. It is only the difference between P1 and P2 readings. Press the P1/P2 switch to toggle between the Two.

It's best to observe the system in a "run cycle" for at least 20 minutes (if it will run that long). A system that will fire and run for 1-2 minutes does not necessarily indicate that is will run trouble-free for 20-30 minutes. When troubleshooting a condensing furnace, you really need to see how well it does in an extended run-cycle and observe how well it drains off the water it creates. Most problems can be traced back to poor or insufficient water management. Anytime the furnace creates water faster than it drains it off, the pressure switch will trip.

Magnum

Tips to Save You Time

As Service Technicians we many times can get caught up in the "rush" to get our calls done and keep the customers happy. The pressure to get everyone Heat and handle all of the Service Calls our dispatcher put on the schedule can be overwhelming at times. In the haste to keep on schedule, what gets missed?

What does it take to making sure every call is complete and doesn't generate a "Call-Back"? I would like to suggest a few things to incorporate in your calls. #1 Have a plan. #2 Be Methodical in your service calls. Check voltages, amp draws, wire connections, gas pressure, Temp rise, use your Combustion Analyzer to see if you're burning clean and at Peak Efficiency, check the Installation Manual to see if the Set-up and Configuration was done completely and properly, was the Flue sized correctly, if it's a Condensing Furnace or has an Evap Coil installed….put a level on it. A Condensing Furnace should be sloped forward 1/2" from back to front. An Evap coil won't drain if it's sloped backwards.

Many times, when we make sure to check all of the obvious and basics, the "strange" and sometimes "unexplainable" issues go away! Yes, it will take a few minutes of your time, but that's what you are there for. To make sure the equipment runs reliably and is adjusted properly. My Grandpa used to say "A Stitch in Time will Save Nine". I'm not sure of the exact reference in his saying, but I know he was telling me to take the time to do it right the first time!

Happy Holidays!

Magnum