York Gas Furnace: PM9 Modulating PSC Re: Control Board Replacement The PM9 furnace is a modulating gas furnace with a standard, PSC blower motor. The original control board had a differential pressure transducer built into the bottom of the board. The new control board utilizes an external...

York Gas Furnace: PM9 Re: Test Mode During normal operation, the furnace input rate can vary between 35% and 100% of full nameplate input, making it difficult to check for proper operation. To help with the furnace startup process, the control has a TEST MODE available that allows the furnace...

York 90% Gas Furnace: PM9 Re: Flashing Code 3 Code 3 = Furnace Pressure Switch failed to close on a call for heat. This gas furnace has one dual-port pressure switch: A pressure switch (PS1) monitors the differential pressure between the inducer and the sealed combustion box (typically...

York 97% Modulating Gas Furnace: PM9 Re: Flashing Code 5 Flashing Code 5 = Rollout Switch or Aux Limit Switch (on inducer) The rollout switches and the aux limit switch are wired in series, so either switch opening during a call for heat will cause a Code 5. Qty Possible Causes: ...

York 90% Gas Furnace: PM9 Re: Flashing Code 6 Code 6 = Multiple Pressure Switch openings during a call for heat. This gas furnace has one dual-port pressure switch: A pressure switch (PS1) monitors the differential pressure between the inducer and the sealed combustion box (typically around...