This condition is probably more common than faults causing low suction pressures, especially during the summer months when ambient temperatures are higher. Causes and corresponding remedial actions are listed as follows.
Air cooled systems
Restricted air flow over the condenser is caused by:
1. Condenser fins blocked by an accumulation of dirt and debris drawn in by the condenser fan(s).
2. Inoperative condenser fan(s).
3. Air in the system if a leak has developed on the low side and the compressor has operated with suction pressures below atmospheric.
4. High ambient temperature.
5. An overcharge of refrigerant.
1 The most effective method of cleaning condensers is by means of a liquid or foam application which penetrates the build-up of the undesirable deposits on the coil and fin surfaces. Brushing the condenser can produce somewhat limited results because of inability to reach the entire surface area.
2. Replacement of fan(s) may be required, or failure may be due to a loose wire or broken electrical lead.
3. This can be verified by stopping the plant and allowing sufficient time for the condenser to cool to ambient temperature. Then refer to a pressure/temperature table and compare the standing or idle pressure with the pressure given by the table. If the idle pressure is higher than that given by the table, air or non-condensables are present in the system. Running condenser fans can speed up the cooling process.
4. High ambient conditions will require a survey of the installation and location of the condenser. Relocation may overcome the problem and provide larger volumes of fresh air. An extractor fan could be installed to remove the discharged air from the condenser, so preventing recirculation. When multiple units are installed, a baffle arrangement to route a fresh air supply over each condenser must be considered.
5. An overcharge of refrigerant cannot develop and must be the fault of the service or installing engineer. Check the standing or idle head pressure in the same manner as for air in the system. The pressure/temperature relationship should conform to the table. The excess refrigerant must be removed from the system.
Water cooled systems
Restricted water flow through the condenser is caused by:
1. Scaling of the interior surface of the condenser water tubing.
2. Incorrectly adjusted or defective water regulating valve.
3. Inadequate water supply: malfunction of recirculating water pump, resulting in poor supply and high water temperature.
4. Air in the system.
5. An overcharge of refrigerant.
1. Descaling of condenser tubing can be carried out by brushing throughthe tubes of a shell and tube condenser. If the scale deposit is heavy, a chemical method is advisable. A shell and coil condenser can only be cleaned chemically. The cost of descaling must be compared with that of a replacement.
2. Check the water inlet and outlet temperatures of the condenser and the water regulating valve operation.
3. Check the water supply pressure and volume.
4. Air or non-condensables present in a water cooled condenser system can be diagnosed very quickly. The water regulating valve, responding to the high operating head pressure, will be supplying a high volume of water to the condenser. When the plant is stopped, water will continue to flow and reduce the temperature of the refrigerant in the condenser. In a matter of minutes the temperature of the refrigerant will be the same as that of the water (the inlet and outlet temperatures will be equal). Compare the idle head pressure with that given in a pressure/temperature table; a higher than normal pressure denotes the presence of non-condensables.
5. Adopt the same procedure as in remedy 4.
If high operating head pressure conditions cannot be rectified by any of the foregoing, it must be considered that the condenser is undersized. It must be replaced, or a subcooler must be installed.