Dometic Furnace Solution

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Learning a little bit - Dometic DFMD35121 furnace
Dometic DMFD35121 2019 Furnace never worked correctly. The fireplace was adequate so did’t use it during our annual trips to winter in FL. In FL crawling over wire web nearly impossible so I cut an access panel (pics in previous post). Now removal / reinstall in 25 minutes. Found loose thermostat wire, fixed and done, I believed.
On the way home 2023 in the NC mountains same as before. Bower runs, gas valve click-on, ignition & heat, gas valve click-off. Blower ran till cool-down complete, furnace off. The heating period would vary a few seconds sometimes longer.
Back home replace Sail SW & circuit board reinstall and test. Again blower on, gas valve click-on, ignition & heat, a few seconds click the gas valve-off no heat, Next remove Unit, replace Limit SW, reinstall and same results.
Same for the Igniter.
Next Gas Valve but this time setup outside bench test. A different gas regulator &10 ft hose. Made sure heat exchanger was clear, a battery beside unit, no thermostat involved. Furnace tested perfect never skipped a beat and ran for 30 minutes. Reinstalled furnace and placed same battery nearby. The same cycling problem again. Then crimped T-Taps for 2 additional wires, one for direct +12 to PCB PWR. Note the +12 to PWR on PCB bypasses the Reset/On SW a Self-Resetting Breaker.
2nd wire for +12 direct to PCB to bypass both Sail and Limit SWs. Intermittent problems are so hard to fix, still suspected the furnace. I surrender quit that’s it, I will not replace blower motor, too difficult, just too much time spent. Bought a 30K Btu replacement. BTW all components except blower motor fit 35K furnace.
Could slide the new furnace in place connect be done. Both have exact same dimensions.
Instead measured position of outside exhaust pipe and see 1/2 inch vertical misalignment with furnace. Made a 1/2 inch base to screw to furnace bottom. Bottom furnace case duct is 5” x 9.5”.
Placed baseplate in position to mark alignment perpendicular to the outside wall. The floor penetration was mispositioned by factory blocking 2” about 20%. Also installers shaved plastic furnace combustion / exhaust cover because of the vertical misalignment. Enlarged floor penetration & made a wall sealing gasket. Tested the old furnace and ran perfectly. The shaved cover may have been a contributing factor.
Installed the new furnace that I like better, it’s more quiet, heats more evenly by running a bit longer. The older hardly used but throughly tested DFMD35212 is available.