I have a York furnace.
model # P2MPD14N08001C
It seems as if the high limit switch is problematic.
It has a rating of 170-30
It is made by Texas Instruments. patent no 5144274
the numbers
1NT17L-2303
L170F-30
025-29041-007A
9418

meaning it shuts off at 170 deg F and comes one when the temp drops by
30 deg F.

The problem seems to be that the downstairs of a 6000 sq ft house does
not get warmer than 67 deg F on a 30 deg F night.

We have about 4 units, in a 2 story house.

Does anyone have any good and cheap suppliers for this part.
I called Grainger, but they could not tell me the cut off temp on the
York high limit switch in stock.