341849-YIM-A-0108
Johnson Controls Unitary Products
13
SEQUENCE OF OPERATION
ANTI-SHORT CYCLE TIMER
This unit has an anti-short cycle timer built in to the
defrost control. This timer will not permit the compres-
sor to start within five minutes after the completion of
the last cycle or power interruption. To bypass the anti-
short cycle feature, short the “TEST” pins together for 2
seconds.
The following sequences of operation are based on
using a standard single-stage heat pump thermostat.
COOLING OPERATION
WITH POWER TO UNIT AND THERMOSTAT IN
COOLING MODE.
1.
If the fan switch on the thermostat is in the “ON” posi-
tion, the 24 volts at “G” will energize the “K1" relay on
the fan control board, close the ”K1" relay contacts,
and energize the indoor blower motor. If the fan
switch on the thermostat is in the “AUTO” position,
the blower will operate only when there is a call for
cooling by the thermostat.
2.
On a call for cooling, the thermostat will send 24
volts to “Y” and “O” on the fan control board. After
the anti-short cycle period is complete,The 24 volt
signal will energize contactor “M1", and the revers-
ing valve solenoid. Power will be supplied to the
compressor and outdoor fan motor, and the revers-
ing valve will switch to the cooling position. If the
fan switch on the thermostat is on the ”AUTO" posi-
tion, the fan control will energize the indoor blower.
3.
When the demand for cooling has been satisfied,
the 24 volt “Y” signal is removed and the “M1" con-
tactor will be de-energized. If the fan switch on the
thermostat is in the ”ON" position, the indoor blower
will continue to run. If the fan switch is in the “AUTO”
position, the “K1" relay will open and de-energize
the indoor blower motor after a 60 second delay,
HEATING OPERATION
WITH POWER TO UNIT AND THERMOSTAT IN
HEATING MODE.
1.
If the fan switch on the thermostat is in the “ON” posi-
tion, the 24 volts at “G” will energize the “K1" relay on
the fan control board, close the ”K1" relay contacts,
and energize the indoor blower motor. If the fan
switch on the thermostat is in the “AUTO” position,
the blower will operate only when there is a call for
heating by the thermostat.
2.
On a call for heating, the thermostat will send 24 volts
to “Y” on the fan control board. After the anti-short
cycle period is complete, the 24 volts signal will ener-
gize contactor coil “M1" and power will be supplied to
the compressor and outdoor fan motor. The reversing
valve will remain in the heating position. If the fan
switch on the thermostat is in the ”AUTO" position,
the fan control will energize the indoor blower.
3.
For units equipped with supplementary electric
heat, if the heat pump cannot meet the demand,
the thermostat “W” will send 24 volts to “W2" on the
fan control board. This signal will also be sent
through the defrost control terminals ”W" and “W1/
66" and back to the fan control ”W1". This 24 volt
signal will energize all stages of electric heat.
4.
When the heating demand is satisfied, the electric
heat will be de-energized when the 24 volt “W”
signal is removed, and the “M1" contactor will be
de-energized when the 24 volt ”Y" signal is
removed. If the fan switch on the thermostat is in
the “ON” position, the indoor blower will continue to
run. If the fan switch is in the “AUTO” position, the
“K1" relay will open and de-energize the indoor
blower motor after the appropriate time delay.
Please refer to Table 17 for more information.
DEFROST OPERATION
The minimum time between defrosts can be field
selected at 30, 60 or 90 minutes. The default time is 90
minutes if the jumper is not installed.
Defrost will initiate when the defrost sensor, located on
the outdoor coil, senses a temperature below 31°F and
when the time since the last defrost is greater than the
selected time on the defrost control. The defrost cycle
terminates when either the defrost sensor reaches
55°F or the unit has been in defrost mode for 10 min-
utes. If the room thermostat opens during defrost, the
unit will resume operation in defrost when the thermo-
stat re-closes.
During the defrost mode, the defrost control will provide
a 24 volt signal from terminal “W1/66" to the fan control
terminal ”W1". This signal will energize electric heat
stage 1, if the unit is so equipped.
For trouble shooting purposes, the defrost cycle can be
manually initiated by shorting the “TEST” pins together
for 5 seconds. Defrost will terminate normally during
the “TEST” mode.
