524581-YIM-I-0512
Johnson Controls Unitary Products
53
down the compressor. The UCB incorporates features to
minimize compressor wear and damage. An
Anti-Short Cycle
Delay (ASCD)
is utilized to prevent operation of a compressor
too soon after its previous run. Additionally, a minimum run time
is imposed any time a compressor is energized.
The ASCD is initiated on unit start-up and on any compressor
reset or lock-out.
Flash Codes
The UCB will initiate a flash code associated with errors within
the system. Refer to UNIT CONTROL BOARD FLASH CODES
Table 28.
Reset
Remove the call for cooling, by raising thermostat setting higher
than the conditioned space temperature. This resets any
pressure or freezestat flash codes.
Electric Heating Sequence Of Operations
The following sequence describes the operation of the electric
heat section.
Two-stage heating:
a. Upon a call for first stage heat by the thermostat, the
heater relay (RA) will be energized. After completing the
specified fan on delay for heating, the UCB will energize
the blower motor. If the second stage of heat is required,
heater relay (RB) will be energized. After completing the
specified fan on delay for heating, the UCB will energize
the blower motor.
b The thermostat will cycle the electric heat to satisfy the
heating requirements of the conditioned space.
Electric Heat Operation Errors
Temperature Limit
If the UCB senses zero volts from the high temperature limit,
the indoor blower motor is immediately energized.
This limit is monitored regardless of unit operation status, i.e.
the limit is monitored at all times.
If the temperature limit opens three times within one hour, it will
lock-on the indoor blower motor and a flash code is initiated
(See Table 28).
Safety Controls
The UCB monitors the temperature limit switch of electric heat
units.
The control circuit includes the following safety controls:
Limit Switch (Ls)
This control is located inside the heater compartment and is set
to open at the temperature indicated in the Electric Heat Limit
Setting Tables 22. It resets automatically. The limit switch
operates when a high temperature condition, caused by
inadequate supply air flow occurs, thus shutting down the
heater and energizing the blower.
Flash Codes
The UCB will initiate a flash code associated with errors within
the system. Refer to UNIT CONTROL BOARD FLASH CODES
Table 28.
Reset
Remove the call for heating by lowering the thermostat setting
lower than the conditioned space temperature.This resets any
flash codes.
For units with VFD and electric heat, the speed of the
indoor blower motor continues to be controlled by duct
static pressure via the VAV control board.
If there are VAV boxes present in the duct system, the
boxes must be driven to the full-open position using a
customer-supplied power source to assure adequate
airflow across the heating elements.
Table 22: Electric Heat Limit Setting
UNIT (TONS)
VOLTAGE
HEATER
kW
LIMIT
SWITCH
OPENS °F
ZJ078, 090
(6.5, 7.5)
208/230
9
150
18
150
24
150
34
150
ZJ102, 120, 150
(8.5,10, 12.5)
18
150
24
150
34
150
54
130
ZJ078, 090
(6.5, 7.5)
480
9
150
18
150
24
150
34
150
ZJ102, 120, 150
(8.5, 10, 12.5)
18
150
24
150
34
150
54
130
ZJ078, 090
(6.5, 7.5)
600
9
150
18
150
24
150
34
150
ZJ102, 120, 150
(8.5, 10, 12.5)
18
150
24
150
34
150
54
130