Service Manual

46
LIQUID LINE SOLENOID ACCESSORY
In heat pump long line applications, a liquid line solenoid is
required to control refrigerant migration in the heating mode.
The solenoid should be installed near the outdoor unit with
the arrow facing the outdoor unit. This is the direction of flow
control. See Long Line Application Guideline for details.
Accessory Liquid Solenoid with Observer Communicating
Wall Control:When using the Observer Communicating Wall
Control, a liquid line solenoid output labeled LS is provided.
Connect the solenoid as shown in the wiring label diagram.
This is a 24vac output that is energized whenever the
compressor is energized. It closes in the compressor- off
mode to prevent refrigerant migration into the unit through
the liquid line.
Accessory Liquid Solenoid with Non- Communicating
Thermostat: The liquid solenoid is connected to the Y and C
terminal connections. The liquid solenoid closes in the
compressor- off mode to prevent refrigerant migration into
the unit through the liquid line.
MAJOR COMPONENTS
Control
Board
The Heat Pump control board controls the following
functions:
S Compressor contactor operation
S Outdoor fan motor operation
S Reversing valve operation
S Defrost operation
S Compressor external protection
S Pressure switch monitoring
S Time delays
Field
Connections
When using the Observer Communicating Wall Control, 4
field wires are required. On single- stage units they are
connected to the factory wires already wired to the
DX+DX- CR terminal (see Fig. 32). Unit as provided by
manufacturer is set up for the Observer Communicating
Wall Control.
When used with a standard non- communicating thermostat,
5 field wires are required to be connected to R, Y, W2, O
and C. Disconnect factory provided wires from DX+, DX- , C,
and R terminals. Using factory provided wires, connect to R,
Y, W2, O and C terminals on the control board. Connect field
24V wires to factory provided wires now connected to R, Y,
W2, O and C and unused factory provided wires.
When using Observer communication wall control only, the
24vac LS (liquid solenoid) output terminal is energized for
the liquid solenoid accessory. The connection is located at
the side of the control board just below the DX+DX- CR
connector.
Compressor Internal
Relief
The compressor is protected by an internal pressure relief
(IPR) which relieves discharge gas into the compressor
shell when differential between suction and discharge
pressure exceeds 550- 625 psi. The compressor is also
protected by an internal overload attached to motor
windings.
TROUBLESHOOTING (SINGLE- STAGE)
SYSTEMS COMMUNICATION FAILURE
If communication between Wall Control, and condensing
unit is lost, the outdoor control will flash the appropriate fault
code. (See Table 13) Check the wiring to the Wall Control,
indoor and outdoor units.
PRESSURE SWITCH PROTECTION
The outdoor unit is equipped with high- and low- pressure
switches. If the control senses the opening of a high or
low- pressure switch, it will de- energize the compressor
contactor, keep the outdoor fan operating for 15 minutes
and display the appropriate fault code. (See table 13)
After a 15 minute delay, if there is still a call for cooling, and
the LPS or HPS is reset, the compressor contactor is
energized. If the LPS or HPS has not closed after a 15
minute delay, the outdoor fan is turned off. If the open
switch closes anytime after the 15- minute delay, then the
unit will resume operation with a call for cooling.
If the LPS or HPS trips for five consecutive cycles, then unit
operation is locked out for 4 hours and the appropriate fault
code (See table 13) is displayed.
In the event of a high- pressure switch trip or high- pressure
lockout, check the refrigerant charge, outdoor fan operation
and outdoor coil (in cooling) for airflow restrictions, or indoor
airflow in heating.
In the event of a low- pressure switch trip or low- pressure
lockout, check the refrigerant charge and indoor airflow
(cooling) and for HP, outdoor fan operation and outdoor coil
in heating.
CONTROL FAULT
If the outdoor unit control board has failed, the control will
flash the appropriate fault code. (See table 13) The control
board should be replaced.
24V BROWN OUT PROTECTION
If the control voltage is less than 15.5 volts for at least 4
seconds, the compressor contactor and fan relay are
de- energized. Compressor and fan operation are not
allowed until control voltage is a minimum of 17.5 volts. The
control will flash the appropriate fault code. (See table 13)
Verify the control voltage is in the allowable range of 18- 30
volts.
COMPRESSOR VO LTAGE SENSING
The input terminals labeled VR and VS on the control board
(see Fig. 32) are used to detect compressor voltage status,
and alert the user of potential problems. The control
continuously monitors the high voltage on the run capacitor
of the compressor motor. Voltage should be present any
time the compressor contactor is energized, and voltage
should not be present when the contactor is de- energized.
COMPRESSOR T HERMAL CUTOUT OR LOSS OF
230V
POWER
If the control senses the compressor voltage after start- up,
and is then absent for 10 consecutive seconds while cooling
demand exists, it will de- energize the compressor
contactor, keep the outdoor fan operating for 15 minutes (if
230v power present) and display the appropriate fault code.
(See table 13) Possible causes are compressor internal
overload trip or loss of high voltage (230V) to compressor
without loss of control voltage.