Service Manual

43
For low ambient cooling with the Observer
Communicating Wall Control the cooling lockout must
be set to “Off” in the Wall Control setup.
Liquid Line Solenoid
When operating in communicating mode the standard
thermostat terminals will not function. A terminal on the
non- communicating thermostat bus labeled “LS” on the AC
control board is provided for wiring liquid line solenoids
when in communicating mode. For operation in
communicating mode wire solenoid valve kit NASA401LS
across LS and C terminals . For operation in
non- communicating mode wire solenoid valve kit
NASA401LS across C and Y terminals.
SINGLE- STAGE HEAT PUMP
(*SH4, *SH5, *SH6)
GENERAL SEQUENCE OF OPERATION -
STANDARD THERMOSTAT
Turn on power to indoor and outdoor units. Transformer is
energized with power supplied.
Cooling
On a call for cooling, a standard thermostat
(non- communicating) makes circuits R- O and R- Y and
R- G. Circuit R- O energizes reversing valve, switching it to
cooling position. Circuit R- Y energizes contactor, starting
outdoor fan motor and compressor circuit. R- G energizes
indoor unit blower relay, starting indoor blower motor on high
speed.
When a standard thermostat (non- communicating) is
satisfied, its contacts open, de- energizing contactor and
blower relay. Compressor and motors should stop.
NOTE: If indoor unit is equipped with a time- delay relay
circuit, the indoor blower will run an additional 90 seconds to
increase system efficiency.
Heating
On a call for heating a standard thermostat
(non- communicating) makes circuits R- Y and R- G. Circuit
R- Y energizes contactor, starting outdoor fan motor and
compressor. Circuit R- G energizes indoor blower relay,
starting blower motor on high speed.
Should temperature continue to fall, R- W2 is made through
second- stage room thermostat. Circuit R- W2 energizes a
relay, bringing on first bank of supplemental electric heat
and providing electrical potential to second heater relay (if
used). If outdoor temperature falls below setting of outdoor
thermostat (factory installed), contacts close to complete
circuit and bring on second bank of supplemental electric
heat.
When thermostat is satisfied, its contacts open,
de- energizing contactor and relay. All heaters and motors
should stop after all fan off delays.
HEAT PUMP SYSTEM FUNCTIONS
AND SEQUENCE OF OPERATION
The outdoor unit control system has special functions. The
following is an overview of the control functions.
SEQUENCE OF OPERATION
Cooling & Heating Operation
This product utilizes either a standard indoor thermostat or
Observer Communicating Wall Control. With a call for
cooling, the outdoor fan, reversing valve, and compressor
are energized. When the cooling demand is satisfied, the
compressor and fan will shut off. The reversing valve will
remain energized until the control board power is removed
or a call for heating is initiated.
NOTE: The outdoor fan motor will continue to operate for
one minute after compressor shuts off, when the outdoor
ambient is greater than or equal to 100_F (37.78_C).
With a call for heating, the outdoor fan and compressor are
energized. The reversing valve is de- energized in the
heating mode.
Communication and Status Function Lights
Green Communications (COMM) Light (Communicating
Control only):
A green LED (COMM light) on the outdoor board (see Fig.
32) indicates successful communication with the other
system products. The green LED will remain OFF until
communications is established. Once a valid command is
received, the green LED will turn ON continuously. If no
communication is received within 2 minutes, the LED will be
turned OFF until the next valid communication.
Amber Status Light
An amber colored STATUS light is used to display the
operation mode and fault codes as specified in the
troubleshooting section. See Table 13 for codes and
definitions.
NOTE: Only one fault code will be displayed on the outdoor
unit control board (the most recent, with the highest priority).
Crankcase Heater Operation
The crankcase heater (when applicable) is energized during
the off cycle below 65_F (37.78_C)
Outdoor Fan motor Operation
The outdoor unit control energizes outdoor fan any time the
compressor is operating (except defrost and intermittently
during low ambient cooling). The outdoor fan remains
energized for 15 minutes if a pressure switch or compressor
thermal protector should open. Outdoor fan motor will
continue to operate for one minute after the compressor
shuts off when the outdoor ambient is greater than or equal
to 100_F (37.78_C).
Time Delays
The unit time delays include:
S Five minute time delay to start cooling or heating
operation when there is a call from the thermostat. (To
bypass this feature in a non- communicating system,
momentarily short and release forced defrost pins.
S Five minute compressor recycle delay on return from a
brown out condition
S Two minute time delay to return to standby operation from
last valid communications (with Observer
communicating wall control only)