1133391-YIM-A-1014
Johnson Controls Unitary Products
49
Figure 31: Cooling Operation Piping Schematic
Normal cooling operation occurs when discharge gas from the
compressor is routed to Condensing coils 1 & 2 located in the
outdoor condensing section. Compressor discharge gas is
condensed to a liquid in the outdoor condensing section and
then continues in the system to the TXV (Thermostatic
Expansion Valve). As the high pressure liquid goes through the
thermostatic expansion valve, the refrigerant is reduced to a
low temperature, low pressure gas/liquid. The cool evaporator
temperature causes the air forced across the evaporator to a
lower temperature/humidity providing a cooling affect.
Refrigerant Recovery Valve #2 (Sol 2) is closed during cooling
operation to avoid short circuiting condenser coil #2.
Refrigerant Recovery Valve #1 (Sol 1) on the re-heat coil is
opened to allow the refrigerant in the reheat coil circuit to return
to the active system.
Figure 32: Reheat Operation Piping Schematic
Reheat operation occurs when compressor discharge gas is
routed through the Reheat coil which is positioned directly down
stream of the evaporator coil. When a call for reheat occurs, the
3 -Way Valve (Sol 3) diverts compressor hot gas to the reheat
coil. Condensing coil 1 and the Reheat coil are active and the
condensing coil 2 is inactive. Refrigerant Recovery Valve #2
(Sol 2) is opened allowing refrigerant to return to the active
system. Refrigerant Recovery Valve #1 (Sol 1) is closed to
eliminate short circuiting during reheat operation. In each mode
of operation a condenser fan motor speed control is used to
control the compressor discharge pressure.
Electric Heating Sequence Of Operations
The following sequence describes the operation of the electric
heat section.
Single stage heating:
a. Upon a call for heating 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.
b. The thermostat will cycle the electric heat to satisfy the
heating requirements of the conditioned space.
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.
Cooling
Operation
Check
TXV
Check
Valve
Valve
ͲͲͲͲͲͲͲͲ
>
ͲͲͲͲͲͲͲͲ
>
Air
Flow
Evap.
Reheat
Cond.
Fan
Cond.
Cond.
ͲͲͲͲͲͲͲͲ
>
Coil
Coil
ͲͲͲͲͲͲͲͲ
>
Coil
1
Coil
2
OPEN
3
Ͳ
Way
Valve
Suction
Discharge
Comp.
CLOSED
Recovery
Valve
#2
Recovery
Valve
#1
Reheat
Operation
Check
TXV
Check
Valve
Valve
ͲͲͲͲͲͲͲͲ
>
ͲͲͲͲͲͲͲͲ
>
Indoor
Outdoor
Indoor
Outdoor
Air
Evap.
Reheat
Air
Cond.
Cond.
Flow
Coil
Coil
Flow
Coil
1
Coil
2
ͲͲͲͲͲͲͲͲ
>
ͲͲͲͲͲͲͲͲ
>
Closed
3
Ͳ
Way
Valve
Suction
Discharge
Comp.
OPENg
Recovery
Valve
#2
Recovery
Valve
#1
