RACA Journal April 2022 | Page 39

Support gauges used by the refrigeration mechanic . Special ( usually electronic ) pressure ( vacuum ) gauges must be used to measure these pressures .

Jabo , it is also important to understand that in order to achieve the required vacuum throughout the system the pressure at the vacuum pump must be reduced to 500 microns absolute pressure .

In practice , in order to ensure that the final pressure inside the entire system is evacuated to the correct level , the plant must be evacuated to 500 microns and then left for at least two hours . If any water is present in the system it will evaporate during this time . This will increase the pressure and further evacuation will be required . If , however , the pressure does not increase to more than 500 microns during this time , the plant can be considered “ dry ”. Jabo , let us move on to the vacuum pump . The vacuum pump for evacuating the system has to be able to reach the vacuum required . To reach a deep vacuum , a two-stage pump capable of reaching a vacuum of 50-100 micron is required ( Minimum 500 microns ).

The vacuum pump must always be checked prior to use . The pump must be able to reach the vacuum required and the oil level must be correct .

Some manufacturers of vacuum pumps recommend that the oil be changed after each evacuation . The oil should definitely be changed if the pump cannot reach the correct vacuum anymore or when it is not going to be used for a long time . Any water in the oil will attack the inside surfaces of the pump which will reduce its effectiveness . Jabo , prior to using a vacuum pump perform the following checks and test :

• The vacuum pump must be suitable for the application and refrigerant .

• The vacuum pump must be checked for safety including the electrical cord , the plug and the extension ( if used ).

• Check oil condition and level when running ( correct if necessary ). The oil should be clear , not milky ( moisture ) or dark-black ( carbon ).

• Using a micron gauge connected directly to the pump , the pump should reach a minimum of 500μ ( microns ) within approximately two minutes .

The pump must be able to reach at least 500μ ( Microns ). If the pump does not reach the required vacuum replace the oil and retest . If the pump is still unable to reach the required vacuum , overhaul or replace it .

Jabo , please note that a hermetic , semi-hermetic refrigeration or air conditioning compressor is not suitable for evacuation as it cannot produce the high vacuum required . Whilst I appreciate the enthusiasm , do not “ make your own vacuum pump ”.

Jabo , in the next issue I will look at the types of vacuum we draw and go into more detail on this subject .

Thank you for all your questions . Send your problems ( and sometimes your creative solutions ) to acra @ netactive . co . za with ‘ Solutions Page ’ in the subject line . You may include pictures . RACA