All Fuel Kit Install Instructions
3
2.2 When the heat pump demand “Y” is satisfied, the room
thermostat will remove the 24Vac from the “Y” termi-
nal and the unit turns off. The defrost board will store
the compressor’s accumulated run time in memory.
2.3 If the heat pump demand “Y” is not satisfied and a de-
mand for furnace operation is initiated, i.e. “W1” ener-
gized, the furnace will be turned on and the heat pump
will be turned off. The defrost board will stop accumu-
lating compressor run time and store the accumulated
time in memory. The “G” demand to the furnace will
be removed and the indoor blower will operate at the
speed designed for furnace only operation. On two
stage furnaces, if a demand for second stage opera-
tion is initiated, i.e.”W2" energized, the furnace will
change to high heat operation. When the “W2” de-
mand is satisfied, the furnace will change to low heat
operation. The furnace will remain on low heat opera-
tion until the “W1” demand is satisfied. At this point,
the furnace will be turned off, the “Y” demand will be
energized to re-start the heat pump and the compres-
sor will start if the 3 minute anti-short cycle delay has
expired. On some digital/electronic thermostats,
“W2” will remain energized until the first stage
demand “Y” is satisfied and then the furnace and
heat pump will be turned off. When the compressor
starts again, the defrost board will start adding com-
pressor run time to the time already stored in memory.
3.0 DEFROST
3.1 During the heating mode, the defrost board in the heat
pump unit will check to see if a defrost is needed every
30, 60 or 90 minutes of compressor run time depend-
ing on the user selectable setting on the board by moni-
toring the state of the defrost thermostat attached to
the outdoor coil.
3.2 When a defrost cycle is initiated, the defrost board turns
off the condenser fan, energizes the reversing valve
and supplies 24Vac to terminals “O” and “W2” of the
AFE18 to turn on the furnace during the defrost cycle.
When the AFE18 receives 24Vac at terminals “O”
and “W2” coming from the heat pump unit and a
“Y” demand is present from the indoor thermostat,
it recognizes that the unit is in the heating mode
and a defrost cycle has been initiated. This is the
only occurrence when the AFE18 will allow the heat
pump and furnace to operate at the same time.
3.3 When the temperature of the outdoor coil rises high
enough to causes the defrost thermostat to open, the
defrost cycle will be terminated. If the defrost thermo-
stat is still closed at the end of the programmed 10
minute override time, the defrost board will automati-
cally terminate the defrost cycle.
3.4 When the defrost cycle is terminated, the defrost board
will de-energize the reversing valve, turn off the fur-
nace and turn on the condenser fan. The unit will now
be back in a normal heating mode with a “Y” demand
for heating. The defrost board resets the compressor
run timer to 0 and starts accumulating compressor run
time from this point. This cycle will repeat itself every
30, 60, or 90 minutes of compressor run time depend-
ing on the user selected time as long as the unit is in
the heating mode.
3.5 The unit will now operate in the heating as described
in section 2 until the “Y” demand for heating is satis-
fied.