Bosch FHP RT-20 Installation, Operation And Maintenance Manual page 46

Troubleshooting – Refrigeration Circuit
Symptom Possible Cause
Refrigerant undercharge.
Blower running backward.
Loose blower, pulley or belts.
Low entering air temperature (low load
condition).
Refrigerant leak.
Low suction
pressure
Evaporator dirty or iced up or airflow restricted.
Plugged liquid line filter-drier.
Improper suction pressure regulator setting.
Expansion valve defective, superheat too high,
or valve too small.
Moisture in system.
Insufficient refrigerant charge.
Defective or improperly adjusted expansion
valve.
Low discharge
pressure
Low suction pressure.
Faulty condenser temperature controls.
Thermostat location or malfunction.
Improper refrigerant charge.
Defective high or low pressure control.
Liquid floodback.
Defective expansion valve.
Compressor
short cycles
Poor air distribution.
High discharge pressure.
Leaking discharge valves in compressor.
Low airflow at evaporator(s).
Incorrect unit selection (oversized).
Always have a completed Pre Start-Up Checklist, unit Start-Up Checklist, and Optional Accessories Checklist prior to requesting parts or
service information.
46 Model RT Energy Recovery Unit
Corrective Action
Check pressures and subcooling.
Interchange any two wires from 3 phase
disconnect.
Check drive pulley alignment, belt tension.
Check entering air wet bulb conditions.
Check system for leaks. Repair leaks and add
refrigerant.
Check defrost system. Clean the coil.
Check fan operation. Check airflow.
Replace filter-drier.
Check setting and correct as required.
Adjust valve for proper superheat or replace the
expansion valve if too small or defective.
Reclaim refrigerant, check for leaks, recharge.
Check subcooling, check for leak. Repair leak
and add refrigerant.
Check superheating and adjust thermal
expansion valve.
See "Low suction pressure".
Check condenser controls and reset to obtain
desired condensing temperature.
Check thermostat, check heat anticipator setting.
Check subcooling, verify superheat.
Check high or low pressure switch.
Possible tight bearings, see above.
Check thermal expansion valve and superheat.
Check ductwork for recirculating.
See "High discharge pressure".
See "High suction pressure".
Check blower operation and airstream
restrictions.
Contact factory.