It got down to 15° F last night. Woke up this morning and it was COLD in our house. 
Checked the furnace and it kept cycling, flames would light and then soon shut off, so I looked through the little window and observed the status LED. I was blinking red 3 times repeated. I had to look up inside the window, as the status LED is actually way up on the top of the circuit board. Why in the world wouldn’t York put the observation window in front of the status LED?)
My Furnace – click on picture for bigger view with labels
I checked the table on the inside of the lower cover, and this fault was listed as “Pressure switch stuck open”.
Fault codes and schematic on inside of lower cover
I wondered if the switch was bad or if something else was wrong, so looked at the schematic next to the fault table and found the Ext Pressure Sensor. It listed the wire colors, so I opened the upper cover and found the connector. I then traced the wires back to the switch, and tapped it and shook it.
The pressure switch.
This changed nothing, so I then disconnected the switch and restarted the furnace. After it cycled, fault LED was blinking red 2 times repeated which is listed as “Pressure switch stuck open”.
I thought about using a jumper to short the connectors on the switch, but was worried I would blow a fuse if shorted it wrong, so after I plugged it all back together I notices there were two ports on the pressure switch, and a rubber hose was only connected to one of them. So I restarted the furnace, and used my mouth to blow and then suck on the open port (poor man’s manometer! )
I noticed that the fan speed would change when I would suck or blow, so I guessed the switch wasn’t actually stuck, so started looking for other problems.
I noticed that when the furnace would start the cycle and the combustion chamber fan would start, it sounded a little like a gurgle. This is high-efficiency furnace that produces a lot of condensation (notice all the water drops on the inside of the clear plastic box in the picture above) so I wondered if there might be a plugged tube somewhere , so I pulled off the black tube that drains the vent pipe, and water started pouring out! So I got the air compressor and blew through the tube to make sure it was draining to main drain tube. I then pulled off the grey tube from the plastic box, and blew compressed air to make sure the box was drained. I then pulled off the yellow cap on on the vent pipe and blew some air to make sure the vent pipe was drained completely. Then I pulled off the main drain tube, and blew air to make sure it was not plugged going to the drain in the floor. Squirted all of them once more for good measure, put them all back together, and then used the air hose to make sure everything was dried out.
Put top cover back in place (since it has switch that shuts off power when the cover is removed) and restarted it. Green LED (normal operation)at first and then went to 2 blinks amber (Normal operation with call for heat) then rapid amber (low flame sense current) when burner first started then back to 2 blinks amber and now is burning beautifully and my house is warm!
Not sure if this was exactly the right thing to do, but it seemed to work and saved me the cost of a service call.