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Do have oil heat if so it maybe the power for cooling and it gets connected to Rc then remove jumper from Rc to R or Rh
No I do not have oil heat is a gas furnace. In the regular connection there were four wires the fifth one is the blue wire.
What coloring wires do you have this below is typical blue could be transformer common will wait to see what you have
R terminal is jumpered to Rc red wire
G terminal is blower green wire
W is heating white wire
y is cooling yellow wire