Control Devices - Lennox WA Series Installation, Operating And Maintenance

8.2 CONTROL DEVICES

Operation
By reacting to compressor discharge pressure, the high pressure sensor monitors efficiency of the condenser. Poor
efficiency, the result of an excessive condensing pressure, is usually caused by :
- A dirty condenser
- Low water flow (in case of water cooled unit)
- Low air flow (in case of air cooled unit)
The low pressure switch monitors the pressure at which the refrigerant evaporates in the evaporator tubes.
Low evaporating pressure is usually caused by :
- Low refrigerant charge
- A faulty expansion valve
- An obstructed liquid line filter-drier
- A damaged compressor cylinder bank unloader.
The control thermostat monitors chilled water temperature at the evaporator inlet. The most common causes of
subnormal temperatures in this zone are:
- Low water flow
- Thermostat setting too low
The oil pressure switch monitors oil injection pressure on the compressor.
Low oil pressure is usually caused by :
- Low oil charge
- A worn or faulty oil pump
- A defective crankcase heater, causing condensation of refrigerant in the oil sump.
The above information does not represent a complete analysis of the refrigeration system. It is
intended to
familiarise the operator with unit operation and to provide him with the technical data required to
enable him
to recognise, correct or report a fault.
Only trained and qualified personnel is authorised to service and maintain this equipment.
Installation - Operation - Maintenance manual (IOM) • AIR COOLED CHILLERS & SPLIT UNITS - 1106-E
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