The AFE18 control is designed for use in heat pump applications where the indoor coil is located above/ downstream of a gas or fossil fuel furnace. It will operate with single and two stage heat pumps and single and two stage furnaces. The AFE18 control will turn the heat pump unit off when the furnace is turned on. An anti-short cycle feature is also incorporated which initiates a 3 minute timed off delay when the compressor goes off. On initial power up or loss and restoration of power, this 3 minute timed off delay will be initiated. The compressor won’t be allowed to restart until the 3 minute off delay has expired. Also included is a 5 second de-bounce feature on the “Y, E, W1 and O” thermostat inputs. These thermostat inputs must be present for 5 seconds before the AFE18 control will respond to it.
An optional outdoor thermostat, OT18-60A, can be used with the AFE18 to switch from heat pump operation to furnace operation below a specific ambient temperature setting, i.e. breakeven temperature during heating. When used in this manner, the “Y” heat demand is switched to the “W1” input to the furnace by the outdoor thermostat and the furnace is used to satisfy the first stage “Y” heat demand. On some controls, if the outdoor thermostat fails closed in this position during the heating season, it will turn on the furnace during the cooling season on a “Y” cooling demand. In this situation, the furnace produces heat and increases the indoor temperature thereby never satisfying the cooling demand. The furnace will continue to operate and can only be stopped by switching the thermostat to the off position or removing power to the unit and then replacing the outdoor thermostat. When the AFE18 receives a “Y” and “O” input from the indoor thermostat, it recognizes this as a cooling demand in the cooling mode. If the outdoor thermostat is stuck in the closed position switching the “Y” demand to the “W1” furnace input during the cooling mode as described above, the AFE18 won’t allow the furnace to operate. The outdoor thermostat will have to be replaced to restore the unit to normal operation.