wiring diagram connecting 90cfm washroom fan to furanace fan using 120 v 60hz relay?

Question

when washroom fan sets on furance fan goes on. washroom fan sets off furance fan back to its normal operation

Answer 1

Well, there's not only one way to wire it, but I guess I would get a single-pole relay with a 120v coil. That should have 5 contacts. Two of them are the coil. One is the relay common, one is normally open and one is normally closed. Take the hot side of the 120v power to the washroom fan/motor and wire that in parallel to one side of the coil on the relay. Attach the other side of the coil to the nuetral for the fan motor (Assuming this is a 120v washroom fan). Now when ever the washroom fan is powered, the relay coil engages. Then for the furnace fan side. You need to know the colors of wires that run from the furnace to the thermostat. Usually the red is 24v hot and green is the fan. So if you were to cross the red and green at the thermostat (or anywhere else) the fan would run. This would not start the AC/furnace, just the fan. So using those two colors you would run a parallel wire from the red wire to the common on the relay and a parallel wire from the green to normally opened side of the relay. Thus, when power was applied to the washroom fan, the relay would close and make the connection from the red wire (24v) to the green wire (fan contactor) and start the fan. If the furnace was already running, it would not change anything. If the furnace was not running, it would start only the fan. When you shut off the washroom fan, the relay would disengage resuming normal (thermostat-controlled) operation of the furnace fan motor.