Why does the blower keep coming on when the Central Air and heater is turned off?

Answer 1

There could be any number of reasons for this. Perhaps, depending on your make and model of furnace/and stat, perhaps the "fan" terminal is energized to circulate the air. That is a simple programming issue. Another would be a short between (normally) the red and green low voltage wires (where red=24v and green is "Fan" (G) terminal at the furnace. Another would perhaps be a problem with the circuit board at the furnace. If you have an older furnace, where there is (normally a honeywell "silver/galvanized enclosure box mounted normally above the gas valve and attached to the furnace) where there is an insertion type combination fan limit switch (you should be able to remove the honeywel coer using just your fingers and find a wheel/dial underneath), this part could be "going out" and would require replacement. If the fan comes on after about 5 minutes after shutting down after a call for heat, perhaps not all of the heat was removed from the furnace and warms up the comb. fan/limit switch again which in turn cycles the blower motor. This too would be a sensitive comb. fan/limit switch and requires replacement. If you have a circuit board, I would try removing all of the 24 volt wires from the (r,g,y,w,c) terminals, just to eliminate any possibility of the stat, or stat wire to be the problem. make sure to put the blower door back in place to ensure the "blower door safety" switch is "closed".