Problems with My goodman gmp075-4 furnace. The blower motor runs regardless of thermostat controls. the induction motor doesn't come on, unless
the limit switch is unhooked...then she spins like a champ. I removed the induction assembly and cleaned it all out, including the flue. The trouble code
flashes consistently, for ïncorrect twinning"ÏNCORRECT PRIMARYPOLARITY". with the recommended check reverse transformer secondary leads reverse primary wires, according to the guide on the cover. Any ideas? I switched the leads on the transformer to no avail. The fuse is ok. It does get cold here in Florida!

Check the polarity of the incoming voltage 120 volts to the unit at the disconnect near the furnace or inside the furnace itself. White should be neutral and black hot leg.

It is also important to check all the ground connections from the main electric panel to the furnace and the grounds made up inside the furnace where they are tied together and where they are landed under a screw head.

Loosen the ground connections and re tighten in all areas especially under the ground screw heads.

NOTE I am talking about the real ground wires not the white neutral wires.

For some reason the limit switch is holding the furnace off.
Test the limit by removing the wires and seeing if it is open.
If it is cool and closed the limit could be defective. They are supposed to be hot as in high temperature when closed and open when cool.

If you have a volt meter you must start at the primary 115 voltage feed to the furnace FIRST to be sure that the black (hot) is really the hot lead. Check from the white (neutral) to the ground (green)...you should NOT have 115 between those two wires. And the black feed is connected to the furnace black (Hot) lead. The question here is what has changed to cause this problem ?? If you are NOT comfortable performing these tests, contact your local HVAC contractor, there may be further issues here. Post back your findings.....