Filed service for packaged ac


FIELD SERVICE OPERATIONS OF PACKAGED AIR CONDITIONER

A. Pressure testing of packaged ac

Pressure testing a refrigerant circuit is essential. Before refrigerant is charged in the system either initially or for topping up gas after a suspected leak. It is advisable to locate the leak, rectify and than charge gas after pressure testing before pressure testing the remaining FREON refrigerant should be removed into an empty cylinder. In case of a compressor winding burnout, the system should be thoroughly flushed with dry N2 to drive out contaminants generated in the system, before the compressor is replaced. It is imperative that a new catchall drier is fitted in circuit.

1. Charge dry nitrogen in the system by connecting cylinder at the compressor service valve and check pressure in the system. Charge nitrogen up to a pressure of 3 to 4 Kg/cm²

2. Check all joints with soap solution. Locate all leaks.

3. If no leak are found, increase pressure up to 10.5 kg/cm² adding more nitrogen. Check for leaks

4. After all leaks are located, remove nitrogen completely by opening charging line. Repair leaks and retest. Do not start work unless entire nitrogen is removed from system.

CAUTION

Never use oxygen gas for pressure testing of refrigeration systems as fatal explosion may occur. Avoid use of CO2 GAS FOR Pressure testing as co2 may contain excessive moisture, which might remain in system. Do not use compressor to feel pressure for leak testing as overheating might damage the compressor.

NOTE

Minor leak  suspected during operating can be located by using halide leak detector.

B. Vacuumising and charging of refrigerant

Evacuating the system by pulling deep vacuum enable dehydrating the system and removing of non condensable air.

In the event of a compressor burnout, it helps to remove carbon deposits and smoke that is generated. A good 2 stage vacuum pump should be employed to get vacuum down to 5 microns (1 microns = 0.001 mm) of Hg absolute. A vacuum gauge for reading vacuum should be used.

1. Put a jumper line To equalise high and low side on the compressor. Connect vacuum pump and vacuum gauge to the refrigeration system. Open compressor services valves and start the vacuum pump.

2. Run vacuum pump till vacuum the boiling point of moisture. Which will be about 0 C temperature. Hence for normal ambient temperature ( 10 C temperature

3. and above pulling a deeper vacuum is neither recommended nor necessary.

4. If vacuum, is stabilised, close charging valve and stop the vacuum pump.

5. Allow vacuum in the system for an hour or so, recheck vacuum, break vacuum by changing refrigerant R 22 from the ¼  inch FPT service port at compressor suction shut off valve. Revacuumise and check. Charge refrigerant as needed by the refrigeration  system.

6. Open the cylinder valve a little and purge air in the charging line by cracking the flare nut at compressor valve port and allowing some refrigerant to drive out air. Tighten the flare nut. Open compressor service valve partially by turning stem clockwise and start compressor. Follow start up procedure.

C. Condenser water requirements

Water cooled condenser should have a soft, filtered water supply. Hard water hardness over 60 ppm of  CaCO3 circulated in the water circuit results in rapid scale formation inside the tube surface. This results in reduction of heat transfer form the Condensing refrigerant to condenser water, thereby resulting in to reduction of system cooling capacity.

Increased refrigerant pressure, clogging of tube and nozzles and eventual break down of air conditioner system. Atmosphere oxygen, carbon dioxide, sulphur dioxide absorbed from the air cooling tower and dissolved in water cause corrosion of condenser.

As the condenser water is recycled the construction of corrosive minerals increases. If repeated operational problems are attributed to the condenser water, than it is advisable, in critical cases, that chemical analysis is asked for rather than frequent descaling operations that would eventually shorten the condenser life. Soft make up water at rate of 1.5% to 2 of flow rate is recommended to be provided at water cooling tower.

D. Descaling of water cooled condenser
Carry out water cooled condenser descaling work when unit is not in operation.
Below precautions should be taken.

1. Do not run blower while descaling is being done. Fumes or gases liberated during descaling with cause discomfort to the occupants and might cause harm to instrument or apparatus kept in air conditioned space.

2. Descaling chemical should be corrected from bottom port of condenser water connections and out  let pipe must be vented as shown.

Add water to the tank and start descaling pump or condensers. Check that there is no leak in the pipe connections.

Add descaling Chemicals slowly to the tank, do not exceed ph of 4 maintain ph valve by checking at regular intervals and adding chemicals slowly. It should take about 2 -3 hours.

Use descaling that is manufactured by vasu chemicals, mumbai or other chemicals if approved by voltas pvt ltd.

After descaling is done, flush the system with  fresh Water.

Inspect the condenser tubes by opening end covers.
Use a nylon brush for brushing tubes if necessary.

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