Anti-short Cycle Timer
This unit has an anti-short cycle timer built in to the defrost con-
trol. This timer will not permit the compressor to start within five
minutes after the completion of the last cycle or power interrup-
tion. 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” position,
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 contac-
tor “M1", and the reversing valve solenoid. Power will be
supplied to the compressor and outdoor fan motor, and the
reversing valve will switch to the cooling position. If the fan
switch on the thermostat is on the ”AUTO" position, 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" contactor 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 de-
lay,
Heating Operation
WITH POWER TO UNIT AND THERMOSTAT IN HEATING
MODE.
1. If the fan switch on the thermostat is in the “ON” position,
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 energize contactor coil
“M1" and power will be supplied to the compressor and out-
door fan motor. The reversing valve will remain in the heat-
ing 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 sig-
nal 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 thermo-
stat 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 Tables 7 and 8 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 out-
door 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 minutes. If the room thermostat opens during de-
frost, 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 manu-
ally initiated by shorting the “TEST” pins together for 5 sec-
onds. Defrost will terminate normally during the “TEST” mode.
Heat Pump Safety Switch Operation
If the unit is equipped with the field installed upgrade safety
package, the refrigeration system will be protected against
high or low refrigerant pressure and low indoor coil tempera-
ture. If any of these three safety switches opens, the unit will be
shut off for the 5 minute anti-short cycle time. Once this has ex-
pired, a six hour elapsed run timer begins. If a second opening
of a safety switch occurs during this six hour period, the com-
pressor will be locked out.
Resetting the lockout function is accomplished by;
1. Removing power from the control's thermostat 1st stage
(Y) input for a time not to exceed 5 seconds (ON-OFF-ON).
2. Removing power from “R” for more than 2 seconds.
3. Shorting the “TEST” pins together for more than 2 seconds.
Electric Heat Limit Switch Operation
The limit switch responds to over temperature conditions in the
air duct. Opening of the device results in dropping power to the
relays. The control logic will also respond by turning off the re-
lays. After four limit cycle trips the unit goes into a 1 hour soft
lockout period. If during this period the control “sees” another
limit cycle, the unit will go into a hard lockout condition. Once in
a hard lockout state, the fan is locked on and the heaters are
disabled. Only a power cycle will clear the state.
During the soft lockout period, the fan responds to thermostat
input but the heaters are enabled. This is to sense a failed
heater relay. The limit cycle count is reset at the start of a heat
request. If the limit remains open for period of 80 seconds or
more, the control is immediately put into a hard lockout condi-
tion. Only a power cycle will clear this state.
Unitary Products Group
15
035-16004-001-A-0202
SECURE OWNER'S APPROVAL
: When the system is functioning properly, secure the owner's approval. Show him
the location of all disconnect switches and the thermostat. Teach him how to start and stop the unit and how to adjust tem-
perature settings within the limitations of the system.
SEQUENCE OF OPERATION
