FORM 145.16-IOM2 (0611)
12 JOHNSON CONTROLS
SAFETY SWITCHES
Each refrigerant system is monitored to ensure it
does not operate outside of its intended operating
parameters. Safety switches are handled as
described below. All system errors override
minimum run times for compressors.
High-Pressure Limit Switch
If a high-pressure limit switch opens, the
microprocessor control de-energizes the
compressor, initiates the ASCD, and stops the
fan. If a call for cooling or heating is still present
at the conclusion of the ASCD, the
microprocessor control will re-energize the
compressor and unit fan.
Should a high-pressure switch open three times
within two hours of operation, the microprocessor
control will permanently lock-out the compressor.
The system must be manually reset by de-
energizing the 24 volt power to unit, or turning the
room t-stat to the “OFF” position then back to
either heating or cooling as required. The
microprocessor control will flash a fault code
indicating a high-pressure lock-out.
Low-Pressure Limit Switch
The low-pressure limit switch is not monitored
during the initial 30 seconds of compressor
operation. After the initial 30 seconds have
passed, the microprocessor control will monitor
the low-pressure switch for another 30 seconds.
If the low-pressure switch fails to close after the
30 second monitoring phase, the microprocessor
control will de-energize the compressor, initiate
the ASCD, and stop the fan.
Once the low-pressure switch has been proven
(closed during the 30-second monitoring period
as described above), the microprocessor control
board will continue to monitor the low-pressure
limit switch for any openings. If the low-pressure
switch opens for greater than 5 seconds, the
microprocessor control board will de-energize the
compressor, initiate the ASCD, and stop the fan.
If the call for cooling is still present at the
conclusion of the ASCD, the microprocessor
control will re-energize the compressor.
Should a low-pressure switch fault three times
within one hour of operation, the microprocessor
control board will lock-out the compressor and
flash a fault code indicating a low-pressure lock-
out.
Freezestat Switch
If the Freezestat switch opens, indicating below
threshold supply water temperature, the
microprocessor control will de-energize the
compressor, and initiate the ASCD. If a call for
cooling or heating is still present at the conclusion
of the ASCD, the microprocessor control will re-
energize the halted compressor.
The microprocessor control board logs the first
incident per compressor request. If the
compressor request is removed, the fault
occurrence counter is reset to zero. Should the
Freezestat switch open twice within a compressor
request cycle, the microprocessor control board
will lock-out the compressor and flash a fault
code indicating a Freezestat lock-out.
Condensate Overflow Switch
A Condensate Overflow fault occurs if the
Condensate Overflow switch was open
continuously for 30 seconds. The compressor is
shutdown regardless of Minimum Run Time,
ASCD is initiated, and alarm 15 is tripped. The
fan continues operating in its current state.
Compressor will re-energize once the
Condensate Overflow switch closes, and ASCD
has been satisfied and a call for cooling is still
present.
The microprocessor control board logs the first
incident per compressor request. . If the
compressor request is removed, the fault
occurrence counter is reset to zero. Should the
Condensate Overflow switch open twice within a
compressor request cycle, the microprocessor
control board will lock-out the compressor and
flash a fault code indicating a Condensate
Overflow lock-out.
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