Air Conditioning Plant Troubleshooting
Air conditioning consists of maintaining the room temperature within the comfort zone. Most package units range in capacity from 3 to 15 Tonnes. The condensers of large units are usually sea water cooled, while the compressor is air cooled, and is a hermetically sealed unit, running on 380 /400 three phase A.C.
The thermostat, with its sensing bulb fixed on the air entry side, serves to cut in or cut out the compressor, to maintain the temperature within the limits.
High / Low pressure switches, over-load relays and water flow switches from the protective circuits, while the hermetically sealed compressor has a winding protection thermostat embedded inside. All controls are connected in series with the 'Hold-on' coil of the starter. The circuit is interlocked with the evaporator fan motor starter, to ensure that the fan is running before the compressor cuts in.
Increase in Discharge Pressure
- This could be due to clogging of the cooling coils for air cooled plants or fouling of the sea water side in the case of water cooled systems.
- Scaling will decrease the heat transfer rate. Cleaning is the remedy.
Problems and Troubleshooting
Reduction in Suction Pressure
- Fouling of the evaporator surface due to dirt leads to an increased pressure drop. This along with fouling of the filter can lead to drop in suction pressure.
- Erratic operation or maladjustment of the expansion valve can also cause a drop in the suction pressure. Reduction of air quantity over the evaporator coil, due to choked inlet filter especially in a dusty atmosphere, can be a major cause of drop in the suction pressure.
- Shortage of refrigerant leads to starving or drop in suction pressure. This also results in overheating of the compressor crankcase, cylinder, valves and cylinder head. The discharge valve manifold will be excessively hot.
- Shortage of refrigerant can also cause an oil return problem.
- In case of hermetically sealed compressors, where the refrigerant is used to cool the winding, shortage of refrigerant can lead to overheating of the windings, breakdown of insulation or even motor burn-out.
- Low pressure at suction also lead to possible air ingress, with further deterioration of the plant performance.
Suction Vapour Superheating
- Excess superheat of refrigerant at the suction of the compressor is undesireable, as it can cause overheating of the compressor. This could be due to a malfunctioning of TEV(Thermostatic Expansion Valve). Bad effects of overheating is already discussed above.
- Voltage fluctuation beyond 10% up and down of the rated, is not permissible, as the windings are not designed for excessive voltages.
- Low refrigerant charge can cause overheating and burn-out, as explained above.
- Quantity of oil, oil with a higher moisture content and acidity, or having insufficient dielectric strength can also cause burn-out.
- Marine Engineering Study Materials
Study Materials on Marine Internal Combustion Engines, Compressors, Heat Exchangers, Air Conditioning and Refrigeration System, Main Propulsion System, Auxiliary Power Generation and Distribution System, Water Treatment, Fresh Water Generator, etc.
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