Gas Furnace Pressure Switch Test

It is designed to sense the negative pressure created by the draft inducer motor during the furnace startup and to shut down the furnace ignition if the air pressure isn t sufficient for removing the exhaust fumes.

Gas furnace pressure switch test.

The pressure switch has a pressure at which it closes which is typically negative. Do not short the pressure switch itself. On a call for heat the inducer should start. Basically the switch needs to be tested to see if it is closing when the pressure diaphragm pulls in.

I explain step by step how to troubleshoot the heater. The furnace then runs awhile longer and this crazy cycle repeats pressure switch glitches open gas shuts off furnace starts another ignition cycle. Using a meter test if the switch closes. To test this recycle the furnace.

Ensure the draft is above the required pressure. To do this the pressure switch wires are removed and the furnace turned on. The second method is to check voltage on the pressure switch while the furnace is running and the third method is to put a manometer in series with the pressure switch to see what vacuum pressure the inducer motor is pulling and if it matches exceeds the rating of the pressure switch. The burners may not burn properly.

When the pressure switch opens the gas valve closes and the furnace starts another ignition cycle because the pressure switch closed after that 1 2 second glitch. Remove the wires from the pressure switch. By this point on an 80 efficiency furnace if you haven t found the culprit you will have to put on your best thinking cap because the issue could be any number of things including a bad board loose or bad wire connections or a bad pressure switch. First turn the power of the furnace off.

Use an ohmmeter to check if the pressure switch is opening or closing properly when heat is called for. The furnace should start. Now use the ohmmeter to check whether the pressure switch is functioning properly. In the hvac furnace video i go over the testing and replacement of a bad furnace pressure switch.

The switch is there to prevent the furnace from running unless the correct venting air pressure is present. A disconnected or damaged pressure switch hose. A furnace pressure switch is a safety device located near the draft inducer motor of a gas forced air furnace. To test the pressure switch use a multi meter and measure the continuity of the switch as it opens and closes.

While the inducer is running short the wires going to the pressure switch with a jumper. Be ready to pull the power. Next take off one of the power hoses and blow on it. A malfunctioning pressure switch.