Johnson Controls SA PD 180 THRU 240 - Manual (Page 18)

430645-YIM-D-0610
18 Johnson Controls Unitary Products
Operation
Unit Control Overview
This series of heat pumps come factory equipped with
Simplicity™ controls to monitor all unit functionality and safety
controls.
Safety Controls
The Simplicity™ control board incorporates features to monitor
safety circuits as well as 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. The
ASCD is initiated on unit start-up and on any compressor reset
or lockout.
The Simplicity™ control board monitors the following inputs for
each cooling system:
• A high-pressure switch is factory installed to protect
against excessive discharge pressure due to a blocked
condenser coil or a condenser fan motor failure. During
cooling operation, if a high-pressure limit switch opens,
the Simplicity™ control board will de-energize the
associated compressors and initiate the 5-minute ASCD.
If the call for cool is still present at the end of the ASCD,
the control board will re-energize the halted compressor. If
a high-pressure switch opens three times within two hours
of operation, the Simplicity™ control board will lockout the
associated system compressors and will flash an error
code (see Table 11).
• A low-pressure switch to protect the unit against
excessively low suction pressure is standard on all
condensing units. If the low-pressure switch opens during
normal operation, the Simplicity™ control board will de-
energize the compressor, initiate the ASCD, and shut
down the condenser fans. On startup, if the low-pressure
switch opens, the Simplicity™ control board will monitor
the low-pressure switch to make sure it closes within one
minute. If it fails to close, the unit will shut down the
associated compressor and begin an ASCD. If the call for
cool is still present at the end of the anti-short cycle time
delay, the control board will re-energize the halted
compressor. If a low-pressure switch opens three times
within one hour of operation, the Simplicity™ control
board will lock-out the associated compressor and flash
an error code (see Table 11).
• An ambient air switch will lock out mechanical cooling at
40
F. If the product was equipped from the factory with
the low ambient option the unit will operate down to 0
F. If
the unit was not ordered with the factory low ambient
option a field installed low ambient kit is available.
The refrigerant systems are independently monitored and
controlled. On any fault, only the associated system will be
affected by any safety/preventive action. The other refrigerant
system will continue to operate unless it is affected by the fault
as well.
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 11.
Reset
Remove the call for cooling, by raising thermostat setting higher
than the conditioned space temperature. This resets any
pressure or freezestat flash codes. Simplicity™ only has
minimum run time in cool. Heat pump mode shuts off
immediately.
Sequence of Operation
Continuous Blower
By setting the room thermostat to “ON,” the low voltage control
circuit from the “R” to “G” is completed and the supply air blower
will operate continuously.
Intermittent Blower
With the room thermostat fan switch set to “AUTO” and the
system switch set to either the “AUTO” or “HEAT” settings, the
blower is energized whenever a cooling or heating operation is
requested. The blower is energized after any specified delay
associated with the operation.
When energized, the indoor blower has a minimum run time of
30 seconds. Additionally, the indoor blower has a delay of 10
seconds between operations.
Cooling Sequence Of Operation
Single-Stage Heat Pump (PC090)
A single stage thermostat is required to operate the heat pump
in cooling mode.
The reversing valve is energized during cooling mode. A
continuous 24V signal is passed through the normally closed
contacts of relay RY2 to the "O" terminal of the Defrost Control
Board (DC). The normally closed relay DR-2 within DC
energizes the solenoid (SOL) of the reversing valve.
When the thermostat calls for cooling (Y1), the Simplicity
control board (UCB) closes the coils of relay RY1 and contactor