An update was made to the WF-EZ3 board in August eliminating the need to add a field jumper wire between T1 and NO terminals when using a variable or multi-speed blower. In the past this added jumper was necessary to get the fan to go to high speed when in electric mode. This update allows high speed fan without having to add the jumper. The problem is when adding this jumper wire to the latest board revision it will cause voltage to feed directly to the heat pump Y terminal, thus causing the furnace and the heat pump to operate at the same time during a heat call.
Please note this update also corrects the issue of certain furnace control boards locking out when “Y” and “W” are both present (reference Field Service Bulletin 1103).
Please click here to view the complete Field Service Bulletin.