5156631-UIM-G-0417
26
Johnson Controls Unitary Products
The control does the following to terminate a defrost cycle.
•
De-energize the reversing valve
Wait 5 seconds
•
Lower compressor speed to 2
nd
stage
•
Energize outdoor fan (which communicates the proper speed).
Wait 30 seconds
•
Ramp compressor speed to 4
th
stage
Wait 5 minutes
•
Take 4 readings starting on the 5
th
minute
•
The Low Pressure Switch is ignored for 120 seconds following
termination of a defrost.
•
Communicate proper speed of compressor (previous speed
before defrost, after calibration)
•
Clear the maximum “Defrost Cycle Timer”
•
De-energize “Y2 OUT” for high ID airflow (unless required by
heating call present, after calibration)
•
De-energize the auxiliary heat outputs (unless required by heat-
ing call present)
•
Reset and restart defrost inhibit timer
COOLING OPERATING ENVELOPE THRESHOLD
ERRORS
The control operates the compressor and outdoor fan with temperature
limitations and toggles
between current commanded speed and thresh-
old error. If an anti-short cycle delay (ASCD) timer is currently active
during any of the below events, it continues in the background and the
system starts after the ASCD timer is satisfied. The errors are cleared
when the outdoor ambient temperature is within the operating ambient
envelope. Threshold errors include the following:
•
Outdoor ambient temperature between 109°
F – 125°
F
(cooling operation)
•
Outdoor ambient temperature greater than 125°
F (cooling oper-
ation)
•
Outdoor ambient temperature less than 35°
F (low ambient tem-
perature cooling operation)
In the event ambient conditions exceed 125°
F, the inverter drive may
enter into a software/protection condition. This can cause the system to
halt operation in order to protect hardware.
Cooling Operation
During cooling operation, the control receives thermostat signals at the
“Y1” and/or “Y2” and “O” input terminals. The control communicates the
proper compressor speed and OD fan speed to the inverter drive,
based on the control operation. The control energizes the “RV” and
“RVG” terminals with 24VAC to switch the reversing valve.
Upon a power cycle or initial power up, the system enters 4
th
Stage
(Nominal). If the outdoor ambient temperature is less than 110°
F
(dependent on compressor run time), the system stages to the 5
th
Stage (Over Drive). When the call for conditioning is removed, the sys-
tem stores an exit comparison based on compressor run time and last
stage of operation. With a new call for conditioning, the system uses the
previously calculated exit comparison with the new active thermostat
call (Y1 + O) or calls (Y1 + Y2 + O) to determine the next stage of oper-
ation. Detailed information pertaining to System Staging can be found in
the Operation Manual.
Low Ambient Temperature Cooling Operation
Low ambient cooling will only function in Normal Operating Mode “N”
between 35°
F – 60°
F. As ambient temperatures decrease, compressor
will maintain Nominal RPM speed and the Outdoor Fan RPM will modu-
late to maintain a constant discharge temperature to stabilize the sys-
tem pressures.
HEATING OPERATION
During heating operation, the control receives thermostat signals at the
“Y1” and/or “Y2” input terminals. The control communicates the proper
compressor speed and OD fan speed to the inverter drive, based on the
control operation.
Upon a power cycle or initial power up, the system enters 4
th
Stage
(Nominal). If the outdoor ambient temperature is greater than -5°
F
(dependent on compressor run time), the system stages to the 5
th
Stage (Over Drive). When the call for conditioning is removed the sys-
tem stores an exit comparison based on compressor run time and last
stage of operation. With a new call for conditioning, the system uses the
previously calculated exit comparison with the new active thermostat
call (Y1) or calls (Y1 + Y2) to determine the next stage of operation.
Detailed information pertaining to System Staging can be found in the
Operation Manual.
Emergency Heat
Emergency Heating mode is defined as a compressor speed reference
of zero and the backup heat source energized. In other words, a 'W' sig-
nal present without any 'Y' signals present. The control energizes 'W1
OUT' immediately when an emergency heat signal “W” is received. The
control energizes “W2 OUT” 15 minutes after the “W1 OUT” output is
energized.
During emergency heating mode, the control returns to standby mode.
The control passes the “W1 OUT” back to the ID unit automatically if no
“Y” is present. The reason is that “W” and “W1 OUT” are connected via
a normally closed relay contact.
PRESSURE SWITCH FAULT & LOCKOUT
High Pressure Switch (HPS) Fault
If the compressor is operating and the high pressure switch is recog-
nized as open, the control de-energizes the compressor output (and the
defrost outputs if they are active). The 5 minute ASCD timer starts when
the compressor speed reaches 0. The compressor contactor remains
off until the high pressure switch has re-closed and the 5 minute ASCD
timer has been satisfied.
If the coil (liquid line) temperature conditions allow defrost to occur
when the control continues the call for heating, the control restarts the
defrost cycle and the timer at the point the call for heating is interrupted.
High Pressure Switch Lockout
If the control recognizes two HPS faults within six hours of accumulated
compressor run-time, the control enter the HPS soft lockout. During the
lockout period, the defrost and compressor relays remain de-energized.
While the control is locked out, the STATUS LED flashes the appropri-
ate code as described in Table 8 and indicates the fault that caused the
lockout condition. Refer to Table 8 for fault code definitions. The control
differentiates between PS faults that occur in heating or defrost modes.
This enables the control to decide which fault code to display. This can
assist the technician in troubleshooting issues with the unit when this
lockout occurs. Otherwise it does not differentiate between heating or
defrost modes when counting PS faults.
The six hour timing starts after the ASCD has expired following the first
PS fault. The timer only accumulates when the compressor is running.
If the control recognizes a second opening of the PS before the six hour
timer expires, the control enters the PS soft lockout. If the control does
not recognize a second opening of the PS before the six hour timer
expires, the six hour timer is cleared and the PS fault counter is reset.
If the system detects four HPS lockouts (a total of eight HPS openings)
within a twelve-hour period, the system enters a hard lockout condition
from which power is needed to cycle for restoration of system function.
Shorting the TEST pins for more than two seconds resets the lock as
well.
