How to test an Air Proving or Sail Switch

[@btknowlton]

This video was created to show someone how to test if an air proving switch is functioning properly, it is not designed to test if your furnaces is developing the correct vacuum. If the furnace being tested indicates an air proving switch fault this is a quick way to test if the switch is good or bad. If the switch is faulty this method will detect it 99% of the time. If the switch is good then the technician should connect a manometer to verify there is sufficient vacuum being created to active the switch.

[@terrywilson1111]

100 times was an exaggeration of course but I have had students test with a digital manometer which will read a max neg. of -19.99 " and they can easily peg it off the scale. And that is inches of water column, not mercury. 1.4 psi would convert to 38.75 inches of water column. I have pressure switches with holes drilled in the casing to simulate a bad pressure switch and they will still close 'sucking in on it' but won't at anything close to the correct amount of vacuum.

[@btknowlton]

The average persons can exert a maximum of 1.4 psi when blowing and less when sucking. This test will check that the contacts are functioning properly and that the diaphragm has not ruptured. If you are capable of developing a vacuum equivalent to 100 inches of mercury with your lungs then I suggest you not attempt this method.

[@terrywilson1111]

This is not the correct way to test a pressure/vacuum switch. There is no way to tell how much vacuum is actually being required for the switch to close, you could easily suck in 100 times the actual amount it should take to close it. A common range is only -0.3 to -0.9 inches of water column. The yellow sticker on the switch will tell you how much vacuum is required for it to close. The proper way is to disconnect the hose from the press sw. and connect it to a digital manometer, then give the furnace a call for heat and while inducer motor is running see how much vacuum the switch is actually seeing compared to what it should take (according the sticker on the switch) for the switch to close. If it is seeing the required amount of vacuum or more (example - requires -0.35 but is actually seeing -.095) and the switch doesn't close then the switch needs replaced. If the switch is not seeing the required vacuum (example - requires -.035 but only seeing -0.15) then the switch is doing it's job and there is a problem elsewhere such as the flue being stopped up, hose or hose nipple plugged, inducer wheel disintegrated, large holes in heat exchanger, etc. etc.

[@bernardocisneros4402]

I think you got your zeros and decimal points in wrong places.

[@davidjohnson2775]

Stumbled across this while looking for something else. It's NOT called a sail switch! It's a pressure switch, a sail switch has a small paddle (sail) positioned within the actual air flow. He's right on 1 thing, he sucks

[@greengreen8176]

this is not a RV.