SYSTEM OPERATION
27
AFE18-60A CONTROL BOARD
DESCRIPTION
The AFE18 control is designed for use in heat pump applica-
tions 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.
break even 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 thermo-
stat 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.
HIGH VOLTAGE!
Disconnect ALL power before servicing
or installing. Multiple power sources
may be present. Failure to do so may
cause property damage, personal injury
or death.
