Temperzone UC8 Troubleshooting Guide
Reverse cycle valve fault protection
Stops a unit from running in the wrong mode if the reverse cycle valve has not switched to the correct
position (cooling or heating). Applied only for air-to-air units. This function has two versions:
Version 1
Applies only to air-to-air units with two pressure transducers (connected to UC8 inputs HPT and LPT)
and with a temperature sensor fitted to the indoor coil (connected to UC8 input IC for packaged units
or connected to IUC input T1 for split units).
Conditions: If the unit is cooling and all of the next conditions are true:
1. The unit is cooling (not off and not de-icing the outdoor coil).
2. The unit operates at more >50% of nominal capacity.
3. The indoor coil temperature sensor reports a temperature that is closer to the
condensing temperature (calculated by the controller from the compressor discharge
pipe pressure) than to the evaporating temperature (calculated by the controller from
the compressor suction pipe pressure)
4. The difference between the condensing- and evaporating- temperatures remains
>20°C for longer than 3 minutes.
If the unit is heating the same list of conditions applies except that the indoor coil
temperature sensor must give a reading closer to the condensing temperature than to the
evaporating temperature.
Version 2
Applies only to air-to-air units without pressure transducers (UC8 inputs HPT and LPT unconnected)
but with temperature sensors on the indoor- and the outdoor- coil (UC8 inputs IC and OC respectively,
packaged units) and to split units without pressure transducers where the indoor unit controller (IUC)
reports indoor coil temperature to the UC8.
Conditions: All of the next conditions must true:
1. The unit is cooling or heating (not off and not de-icing the outdoor coil).
2. The unit operates at >50% of nominal capacity.
3. The measured condensing temperature remains more than 10°C colder than the
measured evaporating temperature (thus the coil temperatures are the ‘wrong way
around’) for longer than 3 minutes.
Overload protection
Protects various components of the system such as the compressor, indoor and outdoor fan motors.
Applies only to units with a low pressure transducer connected to UC8 input LPT.
Conditions: When the overload input signal becomes active.
Overload switches should be wired to input IN#2. The switches should be a normally-on type and, if
there is more than one overload switch, connected in series. When the UC8 overload input becomes
open-circuit the UC8 display shows message OL and the compressor is stopped.
High compression ratio protection
A very high compression ratio can bring a risk of overloading of the compressor motor. The maximum
compression ratio varies between different compressor models, compressors used by temperzone
generally are specified for a maximum compression ratio between 7 and 10. This protection function
will stop a compressor as soon as the maximum compression ratio is exceeded.
Conditions: When the compression ratio rises above the maximum value.
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