As the name implies, preventive maintenance is a planned service program. This helps in minimizing major breakdown, to operate the plant at design efficiency and also to save energy.
Use Non-chemical descaling units to protect the compressor and water lines and save energy.


Half yearly
Keep the heat exchanger surfaces clean,. In case of water cooled condenser, check the leaving temperature difference, if it is more than 12 deg. F or 6.6 deg. C the water tubes are to be changed. The frequency of cleaning the tubes will depend upon the quality of water used. When water used is fairly soft, yearly cleaning will be required. For air cooled condensers check for the LTD at the time of commissioning (during peak summer) and this has to be kept as a guide line. Water under pressure sprayed over the coil is the positive method of cleaning the coil. The water jet the positive method of cleaning the coil. The water jet should be applied in the opposite direction of the air flow.
Cooling coil: The temperature difference between the canvas temperature and the evaporator, (or water leaving temperature) is the criteria to determine whether the coils require cleaning. Cooling coils are to be cleaned with water
under pressure.
Lubricate all moving parts.
Change the compressor oil only if the condition of the same is bad.
Check and clean the contacts in starters. Replace pitted contacts.
Some special service operations.

Refrigerant charging:
If the system has lost refrigerant gas due to leaks, broken connections, etc., this gas must be replaced in order to ensure proper action. It is important that no gas be added until all leaks haves been repaired. Shortage of refrigerant may be indicated by any of the following symptoms.

1. Distinct hissing sound from expansion valve.
2. Low suction pressure and low condensing pressure.
3. Numerous bubbles at the liquid level indicator on the liquid line.
4. Presence of oil at the leaking joint, connection, bolt head etc.

To add refrigerant to the system, follow the procedure below:

1. Back seat the compressor suction shut off valve. Remove the plug from the gauge port. Remove the plug from the gauge port.,
2. Connect the charging line from the refrigerant drum to the gauge port but before tightening the connections, ensure that all air is purged from the line by cracking the outlet valve on the refrigerant drum.
3. Keep the refrigerant drum in a vertical p position with the outlet connection on top so that, only gas can enter the system.
4. Start the compressor. Crack the suction valve off the back seat and open the refrigerant drum valve. Gas will start following into the system.

Charge the systems slowly. Stop the charging every two or three minutes allow the system to stabilize and check suction pressure, lliquid indicator etc. Repeat this process of charging until the system is fully charged.

1. Watch the lliquid level indicator and the suction pressure gauge. When the bubbles disappear and the suction pressure is normal, close the drum valve, back seat the compressor shut off valve, remove the charging line and plug the gauge port.
2. Check the oil level.

Whenever as system is provided with a charging valve in liquid line, it is recommended that this should be utilized in preference to the gauge prot on the suction valve.

Purging of non condensable gases:
A refrigeration system must be kept free from gases other than the refrigerant. The sources for non condensable in a system:

1. Leakage of air into a system operating at a vacuum through leaky joints or on the packing.
2. Residual air in hose connections when adding oil or when charging refrigerant.
3. System not properly evacuated after the system has been opened out for repairs.
4. Possible non condensable in the gas cylinder itself. To avoid this, always get refrigerant from well-established and reputed suppliers.

Non-condensable gases will cause high condensing pressure. This will reduce the refrigeration capacity, increase the operating cost and cause erratic operation of the system. It is necessary therefore those non condensable gases must be purged from the system as soon as their presence is evidenced. In order to determine whether air is present in the condenser, following procedure should be followed:
Pump down the unit. Run the condenser water pump for approximately half an hour to allow the condenser to cool down .Install a pressure gauge on the discharge service valve. After the water has circulated in the condenser for some time, its temperature and the pressure in the condenser will both be about steady. Determine the saturation pressure, it is clear that the non-condensable gases are present sand the system should be purged trough the purge valve provided on the top of the condenser.Back seat the purge from its outlet connection on this valve.

• Disconnect the gauge from its outlet connection on this valve.
• Slowly turn the valve stem off the back seat from one to two turns. Air will blow off if this is done slowly.
• Run the condenser water pumps and read the pressure in case of discrepancy repeat the purging till the saturation pressure corresponding to the water temperature is obtained.