Installation manual

035-19084-001-D-0504
Unitary Products Group 57
ELECTRIC HEATING SEQUENCE OF OPERATIONS
The following sequence describes the operation of the
electric heat section.
Single-stage heating (applies only to 18 KW heater, all
other heaters MUST use a two-stage thermostat):
a. Upon a call for heat by the thermostat, the heater
contactor (6M) 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.
Two-stage heating (applies to all heaters except 18
KW):
a. Upon a call for first-stage heat by the thermostat, the
heater contactor (6M) (6M & 7M on 72 KW, 240V)
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 con-
tactor (7M) will be energized. Note that on the 54
KW, 240V heater, heater contactors (7M & 8M) will
be energized and on the 72 KW, 240V heater,
heater contactors (8M & 9M) 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.
FIGURE 21 - SYSTEM PIPING SCHEMATIC
C1
TXV
FS
LPS
HPS
Condenser
Fan
Air Flow
Air Flow
Air Flow
Hot Gas Re-Heat
Solenoid Valve
Indoor Blower
Bleed Line to clear
the Hot Gas Coil
when it is not in use
Evaporator
Coil
Hot Gas
Coil
Compressor
Piping T
Piping T
Check
Valve
Condenser
Coil
Check
Valve
Sol 2
Suction line
bleed
Open in
Reheat
Open in
Cooling
HPS
(Sol 3)
Sol 1
Refrigerant flow in reheat mode
Refrigerant flow in cooling mode
Accumulator