Furnace Troubleshooting: What to Check When There's No Voltage at the Pressure Switch

a man works on the connections of a furnace

When you find yourself with no voltage at the pressure switch, you will want to do a little bit of furnace troubleshooting to get an idea of what went wrong. While this is something that anyone can do in their home, you still may want to contact a professional to make sure there aren’t any serious problems once you are done. You will need to make sure that you have an ohm meter to use for the readings while you are troubleshooting the furnace.

The ohm meter can be found online or at a hardware store. If at any step of the way you feel something is wrong, stop what you are doing and contact a professional so that you do not do any more damage to the furnace. Here are a few things to keep in mind to help you work out the problem.

Check for Open or Close

You want to check to see if the pressure switch opens or closes when you look with an ohm meter. The switch it typically open when it starts and it should close when you attach the ohm meter to it. Be sure that you are attaching each terminal to the ohm meter to get the correct reading. If you aren’t getting a reading at all, this could be because you don't have the ohm meter set up properly. If this is the case, take it off and then re-attach each terminal. If you are still having trouble, then there may be a problem with the meter.

Check the Number

The number on the ohm meter is also an important thing to look at. You want to make sure that the number is lower and closer to zero. A two would be an acceptable number for a pressure switch with voltage. If you find that you are having trouble reading it or that the number is extremely high, you will want to check to see if the pressure tube is cracked, the impeller is defective or if the switch itself is defective. It is hard from just the reading to tell which one it is, but you have a good place to start. While many meters do differ, you will likely have a similar scale. Just be sure that you are keeping the readings on the lower end of the meter.

Once you are finished checking, you will want to remove it from the ohm meter, one terminal end at a time. If you have any troubles be sure to consult the instructions that come with the ohm meter to help you out. If you have never worked with an ohm meter before, it may be helpful for you to get a little practice as well as go over the manual before you begin trying to make readings.