TemperZone UC8 Troubleshooting Guide

Temperzone UC8 Troubleshooting Guide
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Low compression ratio protection
For proper internal circulation of the compressor lubrication oil compressors require a minimum
compression ratio or a minimum pressure differential. The exact minimum value varies between
different compressor models but generally falls in the range of 1.2 to 1.5. This protection function will
stop a compressor when the required minimum high-to-low pressure ratio is not achieved after a
certain time interval.
Conditions: When the compression ratio remains below the minimum value for longer than 3
minutes. Applied only during normal cooling or heating; not applied when the unit is
de-icing the outdoor coil.
16. Lock-out
The controller counts the number of trip events for each of the safety functions. If any one of the trip
counters listed below reaches the count of 3 then the unit is put into lock-out mode. During lock-out
mode the compressor and the fans are not allowed to run. The display will show which protection
caused the lock-out and the fault relay output will be on.
Trip event counters are reset to zero when the thermostat calls for the compressor to be off and also
when mains power to the controller is switched off and on again. A trip event is also removed from
the count if the event occurred longer than 12 hours ago.
Faults that can lead to lock out are:
 HP
 LP
 High temperature protection
 Frost protection
 High suction line / evaporation temperature protection
 Low discharge superheat protection
 High discharge superheat protection
 Freeze protection
 Reverse cycle valve failure protection
 Variable speed compressor driver trip events
 Low compression ratio
 High compression ratio
Lock-out can be cleared in a number of ways:
 By removing and then restoring mains power to the UC8 controller.
 By Modbus RTU command sequence. Refer to document UC8 Modbus communications for
details.
 By BACnet command sequence. Refer to document UC8 BACnet communications for details.
When a unit was locked out and the UC8 controller is reset, e.g. by removing and then restoring mains
power, the display will show the previous fault message for 20 seconds (after the normal start-up
sequence). After that normal operation resumes. The 20 second long message display will repeat
every time mains power is removed and restored until the unit has completed at least one normal
compressor-on / compressor-off cycle.
If a unit repeatedly locks out (and is then unlocked) whilst the unit is never able to complete a normal
cooling or heating cycle, then as the unit locks out for a third time in a row it becomes “permanently”
locked. If this has happened then, to re-activate the unit, the UC8 pushbutton must be pressed and
then the unit must complete at least one full cooling or heating cycle (that is: compressor must start
and then then stop the normal way, e.g. under control of a thermostat).

TemperZone UC8 Specifications

General

Brand	TemperZone
Model	UC8
Category	Controller
Language	English