Specifications

164015-YIM-A-0905
54 Unitary Products Group
Compressor Protection
In addition to the external pressure switches, the compressors
also have inherent (internal) protection. If there is an abnormal
temperature rise in a compressor, the protector will open to shut
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 29.
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 29).
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 21 and 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 29.
Reset
Remove the call for heating by lowering the thermostat setting
lower than the conditioned space temperature.This resets any
flash codes.
Electric Heat Anticipator Setpoints
It is important that the anticipator setpoint be correct. Too high
of a setting will result in longer heat cycles and a greater
temperature swing in the conditioned space. Reducing the
Table 22: Electric Heat Limit Setting 50” Cabinet
UNIT (TONS) VOLTAGE
HEATER
kW
LIMIT
SWITCH
OPENS °F
ZH102, 120, 150
(8.5, 10, 12.5)
208/230
18 150
24 150
34 150
54 130
ZH102, 120, 150
(8.5, 10, 12.5)
480
18 150
24 150
34 150
54 130
ZH102, 120, 150
(8.5, 10, 12.5)
600
18 150
24 150
34 150
54 130
Table 23: Electric Heat Limit Setting 42” Cabinet
UNIT (TONS) VOLTAGE
HEATER
kW
LIMIT
SWITCH
OPENS °F
ZH078, 090 (6.5, 7.5) 208/230
9135
18 150
24 165
34 190
ZH078, 090 (6.5, 7.5) 480
9135
18 150
24 165
34 185
ZH078, 090 (6.5, 7.5) 600
9135
18 150
24 150
34 185