I only have a white, red, green and yellow wires, from my old thermostat. I see multiple Red wires… where does a single red wire go… to the R connection…
Wiring – Switching from a Mercury Switch Thermostat to a XT500C Thermostat
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Related Solutions
See below, if you jumper Yellow to White the heat strips will run in both cool and heat as Yellow is energized in both modes, what makes it a cooler or heater is the O being energized in cool mode Rheems use the B terminals to be energized in heat.
Connect the blue wire from the thermostat cable, to the C terminal in the furnace. Then connect the blue with at the thermostat, to the C terminal of the new thermostat.
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Best Answer
You need to jumper the red wire to both Rc and Rh. The Rh powers the heating side and the Rc powers the cooling side. Since you have a four wire system, they use the same power supply therefore they need to be jumpered. I believe your XT500C takes batteries. If so you don't need to connect the common (C) terminal. If you do need the C comment back a I will guide you to a resolution.
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I suppose you should safely dispose of the mercury at a waste facility. My Dad and I have been keeping mercury from old thermostats in a jar for collectively 70 years.