I installed a Totaline P474-1050. I followed the instructions for a 4 wire (red, green, white, and yellow) thermostat (the wire between the thermostat and the furnace has 5 wires but the fifth wire blue/black, is not connected on either end). Once connected, I tested the A/C portion first and just as the manual indicated might happen, the display went blank. I installed the resistor on the furnace end. There was not terminal strip only connections with wire nuts. This fixed the display issue going blank when the A/C comes on, but now the display goes blank when the heat comes on ugh
I was wondering if I should convert this to a 5 wire installation, using the unused wire, connecting it to the C which I believe is 24v AC comman.