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Does the small inducer vent fan come on when you call for heat?
OK, This indicates that the pressure switch is not closing.
Below is a flow chart listing causes and corrective steps.
Lets start by removing the hose and blowing through it to make sure it is clean.Use a straightened paper clip to clean little barbed fittings.We will go from there.
Any water in the hoses at all? Go ahead and with hoses attached to switch suck and blow on them and see if you hear pressure switch click
If switch does not click you most likely just have a bad switch.Contacts not closing.Do you have a volt meter to see if the switch is closing?
Ok if switch clicks that is good.Now reconnect hoses and try furnace listening to see if you hear the clicks when inducer starts rather than by sucking.
Fan should not be going on and off,It should stay on entire heat cycle. Do you have a meter to see if we are losing voltage to inducer?
OK your problem is the pressure switch is not staying closed.You will have to get a tech in with a meter to troubleshoot to determine why motor is cutting off and pressure switch not closing.
Great. What we wan to do is check leads to meter for 120 volts and see if the voltage is dropping out when fan stops.
OK if we are only getting 23v to motor this is an issue with the control board,It should be sending 120v the entire time furnace is calling for heat.
Most likely will have to replace board.If it is something you want to do you can do yourself, but I would feel more comfortable having an onsite tech verify.
Wish it were a simple fix like condensation or debris in the hose, but since motor is quitting seems to be more involved.
If you have further questions, please let me know.
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OK is the 120 staying constant when motor quits? You stated "It clicks and the fan comes on, the fan stops momentarily, then it clicks again and the fan again comes on "