Troubleshooting with Microprocessor
(Not Include Carel Controller)
Symptoms Possible Causes Remedial Action
1. PCB display ‘CO’
x Compressor thermal relay tripped
x Terminal loose
x Reset the thermal relay and carefully
monitor unit operation when it is
restarted
x Tighten terminal screws.
2. PCB display ‘PO’
x Pump thermal relay tripped
x Terminal loose
x Reset the thermal relay and carefully
monitor unit operation when it is
restarted.
x Tighten terminal screws
3. PCB display ‘FL’
x Flow switch connection loose
x Water volume too low
x Wrong direction of water flow
x Tighten terminal screws
x Add water into the system
x Interchange power input phase
4. PCB, display ‘HP’
x Discharge pressure too high
x Overcharge
x Coil dirty
x Condenser fan does not work
x Expansion valve stuck in open
position
x Reset the pressure switch and
observe the unit operation when it is
restarted
x Contact local dealer
x Clean the coil with chemical
detergent
x Contact local dealer
x Replace it
5. PCB display ‘LP’
x Suction pressure too low
x Undercharge
x Gas leak
x Water flow rate too low
x Reset the pressure switch and
observe the unit operation when it is
restarting.
x Contact local dealer
x Contact local dealer
x Adjusting the flow rate
6. PCB display ‘E3’
x Antifreeze protection activated.
x Water flow rate too low
x Bubble in the heat exchanger
x Check the temperature setting
x Adjusting the flow rate
x Increase the water volume
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