McQuay IM 660-3 11
Diagnostic Service
Low Pressure Faults
The “Low Pressure” fault indicates that the low pressure
switch input (J4-11) sensed an open circuit while the controller
was calling for the compressor to run. The low pressure switch
opens when the temperature falls below its set point. For
information on troubleshooting digital input faults, see “Test
Procedures” on page 12.
Effects:
• The compressor immediately de-energizes.
• The software disables normal unit operation until the fault
condition is manually corrected.
Condensate Overflow Fault
The “Condensate Overflow” fault indicates that the condensate
overflow sensor (J4-14) sensed a grounded signal while the
controller was calling for the compressor to run. For
information on troubleshooting analog input faults, see “Test
Procedures” on page 12.
Effects:
• The compressor immediately de-energizes.
• The software disables normal unit operation until the fault
condition is manually corrected.
Brownout Fault
The “Brownout” fault indicates the water source heat pump is
sensing low voltage levels. It is designed to protect the
compressor and contactors from low line voltage or
“brownout” conditions.
The controller is programmed with a brownout set point that
corresponds to 82% of the water source heat pump’s nameplate
line voltage value. If the water source heat pump controller
senses a voltage level less than its set point for more than 1
second, it triggers the brownout fault. The fault resets
automatically when the sensed voltage remains at or above a
level corresponding to 90% of the nameplate value for a period
of 1 second. For information on troubleshooting this alarm, see
“Test Procedures” on page 12.
Effects (as applicable):
• The compressor immediately de-energizes.
Change Filter Notification (network units
only)
The “Change Filter” notification indicates that the fan has
operated longer than the set number of hours. Typically, this
warning is used to alert the building operator to replace the
filter. To clear the notification, reset the filter timer at the
network PC.
Effect:
• An alarm message identifying the water source heat pump
network address and time of occurrence is sent to the
network printer.
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