Try softly blowing into the switch. Does it click? If not then it probably does not work. Use an ohm meter and verify the switch is bad, while blowing into the hole.

If you want to troubleshoot appliances and HVAc controls you need a multimeter that does AC-DC volts, and ohms. A cheap one is available at HD or Lowes for under $20. My last digital cost $5 from Harbor Freight. Either is good for troubleshooting.

I let someone use the Digital meter and they blew it up. It will cost too much to replace the meter. A professional quality meter can cost over $500, and you can basically do the same thing. The cheap meter is also good for automotive on the DC range.

Could be air switch, or could be that you got alot of wind that night when furnace tried to fire and locked-out .

1) pressure switch fault code

remove hose from induce draft motor pivot tube/blow soft into hose and you can hear diaphram inside switch pop closed.
Next:
need a paper clip / or small solid wire to insert into pivot tube on induce draft motor to insure to debris are stopping up hole.

Next :
Check your B-Vent to roof from furnace to insure NO birds nest or clogs.

un-plug furnace/ or cut power for 5) minutes.
After 5)minutes go to thermostat call for heat 74* and watch furnace sequence of operation.
1) Induce draft motor-comes on
2) Air switch/made close
3) Spark ignition/or hot surface ignitor
4) Gas Valve opens
5) flame sensor /insure that flame is there or gas valve off.
6) 90 seconds after call for heat blower comes on.

Good Luck and be careful.

Here is a link that might be useful: hvac-mechanic

Bob,

I have a meter. What setting do I use on the meter? Where do I make the connections for the leads?

THanks

Oh Jeez...This post is scaring me! If you don't know what setting to use on a multi-meter and not a clue were to touch the leads on the switch then you need to call in a Technician and let them fix it! These are simple things for a qualified tech. Not saying a homeowner can't do it but by the questions you are asking tells me that you really are not qualified and are taking a chance at damaging the equipment and also yourself!

Using a meter is something to learn. Anyone can learn how to use a meter. Do not touch the ends of the probes. You will affect the circuit or possibly get hurt.

If you do it wrong, you will possibly damage something. When using an ohm or the symbol that looks like an upsidedown horseshoe, all power needs to be dead. The ohm scale has a battery. Ohms are the same thing as continuity. Continuity needs to be zero ohms. This means you need to have the needle on the 0 line. If you have multiple ohm settings use the lowest x 1 scale. Higher scales will not allow you to make a good test.

Before making this test adjust the meter so that when you touch 2 leads, the needle is on the zero mark. Do not touch the leads with your body, because the body will skew the reading. It is very important to have zero ohms. Not 3, or 5, or even 10 ohms. Maybe 1 ohm is ok. Not always.

This means a circuit is a closed loop that has a meter and battery internally connected, to test probes that touch each of 2 connections of a simple switch. By connecting to the switch, this completes the circuit when the switch is closed.

One side of the switch connections needs to be removed to do the test. If you have 3 connections on the switch, one is a common and one switch is open until air. The other connection is closed until air. This is known as a momentary NO-NC switch. NO-Normally open, NC-Normally closed. When the switch has 3 connections, all connections need to be labeled and removed to insure you make a valid test.

When the switch opens and closes this is the same as a lightr switch. It either completes the circuit or opens a circuit. An air diaphram is a simple open and close switch.

When air blows into the switch the switch closes and the meter needle goes to 0 ohms on the scale. The same as touching the 2 leads together.

Remember for ohms testing the power needs to be off. This means either unplugging the furnace or triping the breaker.

You will damage the meter otherwise.

Most meter have multiple scales. Look for the scale that has a upsidedown horseshoe or the greek symbol for omega.

As a final warning, Ohms are not the same as voltage. Making a voltage test on the ohms setting will surly ruin the meter. This is not a voltage test, nor is this the way to test voltage.

Fer cryin out loud this person is freezing their ass off and here someone is giving them instructions on how to use a meter to check something they don't have a clue about!!! What if the darn draft motor is NFG? There is no diagnostic for that but but the switch sure as hell won't close. And thats all that would show up on the board, "pressure switch stuck open", it doesn't say why! Keep going Bob, maybe have this person blow into the tubing to initiate ignition without a draft inducer. Then they could go to another forum and learn how to draw eye brows to replace the ones that got burned off screwing around with a piece of equipment they kow nothing about.

Hey, I just had an eyebrow failure! Hair is okay though.

Anyone who has ever had a flame roll out in their face knows there is no humor there. Toasted eyebrows are the least to be concerned about.

*points at phone book*

call a qualified technician

i had same problem found out water builds up in
rubber tube pulled rubber tube off at switch
drained water out it started working
before it stopped it started turning burner off
and on it cost me $88.00 TO FIND THIS OUT
it happens a few times in winter now i just
drain it every month they say they know about it
and dont have a fix for it yet i just dont like them taken
atvantage of someone when they know its going to do it
when they sell you the furnace
at $88 a pop i just drain it my self no tools
just pop the door off and drain it put it back on
and ready to go.