The furnace thermostat wiring is most likely running overhead to the A/C unit. However it could be ran under the floor but that's not normal.
They normally run the furnace wiring to the A/C and then run a multiconductor cable from the A/C to the thermostat. If it's a Dometic A/C and thermostat, then the furnace wires have to run from the furnace to the A/C because that's where the control relay for the furnace is.
Which Furnace, A/C and Thermostat do you have?
Can you post a picture of the wiring at the thermostat? Is it one cable or two?
Salem 29RKSS Pushing a GMC Sierra 2500HD!
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