268723-BIM-C-0908
16
Johnson Controls Unitary Products
Heating Sequence Of Operations
1.
When the fan switch on the thermostat is in the “ON”
position, the 24 volts at “G” brings on the indoor blower
motor at the heating flow. When the fan switch on the
thermostat is in the “AUTO” position, the blower operates
when there is a call for heating by the thermostat.
2.
On a call for heating, the thermostat sends 24 volts to “Y” on
the fan control board. After the anti-short cycle period is
complete, the 24 volt signal energizes contactor coil M1 and
power is supplied to the compressor and outdoor fan motor.
The reversing valve remains in the heating position. When
the fan switch on the thermostat is in the “AUTO” position,
the indoor blower is energized at the heating airflow.
3.
For units equipped with supplementary electric heat, when
the heat pump cannot meet the demand, the thermostat
“W” sends 24 volts to “W2” on the fan control board. This
signal also is sent through the defrost control terminals “W”
and “W6” and back to the fan control “W1”. The 24 volt
signal energizes all stages of electric heat.
4.
When the heating demand is satisfied, the electric heat is
de-energized when the 24 volt “W” signal is removed, and
the M1 contactor is de-energized when the 24 volt “Y”
signal is removed. When the fan switch on the thermostat
is in the “ON” position, the indoor blower continues to run.
When the fan switch is in the “AUTO” position, the indoor
blower motor ramps down over a 15-second period.
Please refer to Tables 14 and 15 for more information.
Defrost Operation
The demand defrost control implements a temperature
differential (”delta-T”) demand defrost algorithm. The heat
pump is allowed to operate in the heating mode until the
combination of outdoor ambient and outdoor coil temperatures
indicate that defrosting is necessary. When coil temperature is
below the initiate point for the ambient temperature
continuously for 4-1/2 minutes, the heat pump is put into a
defrost cycle. This 4-1/2 minute timer eliminates unnecessary
defrost cycles caused by refrigeration surges such as those
that occur at the start of a heating cycle.
A timed inhibit feature prevents the system from responding
to a call for defrost less than 20 minutes after the initiation of
the previous defrost. After the 20 minute inhibit time has
expired, temperature conditions must call for defrost
continuously for 4-1/2 minutes before a defrost cycle is
initiated. A temperature inhibit feature prohibits defrost if the
coil temperature is above 40°F.
A forced-defrost feature puts the system into a defrost period
every 6 hours and 4 minutes to recirculate lubricants, unless the
coil temperature is above 40°F. All defrost timing occurs only
while the compressor is on.
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.
Figure 9: Demand Defrost “Curve” Selection Jumper
Heat Pump Safety Switch Operation
The unit is equipped with a safety package. The refrigeration
system will be protected against high or low refrigerant
pressure. If either of these safety switches opens, the unit will
be shut off for the 5 minute anti-short cycle time. Once this has
expired, a six hour elapsed run timer begins. If a second
opening of a safety switch occurs during this six hour period,
the compressor 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
relays. 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 this 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
condition. Only a power cycle will clear this state.
Table 13: Demand Defrost Selection
Unit
Pin Position
B*UZ 036, 048, 060
1
B*UZ 024, 030
2
B*UZ 042
3
TEST
T
N
E I
B
M
A
G
B
M
A
G
L I
O
C
L I
O
C
1
2
3
4
D
N
O
C
N
A
F
E
G
A
T
L
O
V
H
G I
H
PRESSURE
M
SWITCH
REV
VALVE
X/L
R
C
Y
O
W
W1/66
L /
X
R
C
Y
O
W
6
6 /
1
W
DEMAND
DEFROST
SELECTION
JUMPER
(JUMPER
IS SHOWN
IN POSITION
#1)
