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 AIR CONDITIONING (Vacuum Pump Maintenance)


Vacuum pump maintenance :-

Vacuum pumps need regular oil changes to ensure optimum performance and long life. The period between changes will vary depending on the condition of the refrigeration and air conditioning systems that vacuum pump is fitted to. The dirtier / wetter the system, the quicker the vacuum pump
will require its oil changed. Constant monitoring of the condition and level of the oil in the pump is required.


Evacuating a system is important to make sure the system operates at its optimum design performance. Evacuating a system removes moisture, air and non-condensables from the system. Removing these impurities from a system is important..


Most, if not all split air conditioning systems today are pre-charged. That is a specific amount of refrigerant has been factory charged into the outdoor unit ready to be released into the system. Before this can be released into the system, it is mandatory that system be evacuated using a refrigeration vacuum pump. A refrigeration vacuum pump is a specialised tool that is capable of pulling vacuums on a system to the required levels stated in the Refrigerant Handling Code of Practice 2007 HB40 2007 Part 2.

Moisture in a system can cause problems such as:-

  • Moisture (water) can freeze at the expansion point (capillary tube, accurator piston etc.) and partially block refrigerant flow through the device.
  • Moisture mixed with chlorine based refrigerants (such as R22) can form hydrochloric acids. This acid greatly increases the corrosion of metals and could possibly cause copper plating. Heat increases the rate of corrosion due to acids because at higher temperatures the acid-forming process accelerates.
  • Refrigerant oil presents another problem caused by moisture. Refrigerant oil is an exception to the rule that "oil and water don't mix‟. In fact, refrigerant oil has an attraction for moisture and will absorb it rapidly if left open to the atmosphere. Water formed acid mixes with refrigerant oil, the two forming a closely bonded mixture of fine globules. The effect is called "sludging‟ and greatly reduces the lubricating ability of the oil.
  • Polyol Ester (POE) and Poly Alkylene Glycol (PAG) oils are particularly susceptible to moisture ingress; therefore these systems must be evacuated to a particularly low level.

Non-condensables in a system can cause problems such as:-


  • Reduce condenser capacity subsequently reducing overall system capacity and performance.
  • Cause the compressor to with run higher discharge vapour temperatures which can reduce the life of the compressor.
  • Because of higher discharge temperatures, refrigerant oil can be affected.

A system must be evacuated to the level required by the manufacturer. However, to comply with current Federal Government legislation, it must be evacuated to a minimum level of 500 microns. This is documented in the Refrigerant Handling Code of Practice 2007; HB40 2007 Part 2. Systems other than self contained low charge systems.


There are two common methods of evacuation and dehydration;

  • they are the Deep Vacuum and
  • the Triple Evacuation Methods.

Deep vacuum method:-

In this method the refrigeration system is evacuated to 500 microns and isolated. The system should left to stand for a minimum of 60 minutes with only maximum rise of 100 microns (HB40 2007 Part 2). If the vacuum has held with only this acceptable amount of rise occurring, then the system is now considered dry and the refrigerant can be now charged into the system.


Triple vacuum method:-

Because of the time duration of "deep evacuation‟, triple evacuation is usually the most popular method of evacuation. As the name indicates, in this method the system is evacuated three times. The first evacuation is done to 5000 microns and the vacuum is broken by filling the system with dry nitrogen. The system is then evacuated again to 5000 microns and the vacuum is again broken with dry nitrogen. A third and final evacuation of the system to 500 microns is carried out, with this vacuum being broken with refrigerant being charged into the system.


A vacuum pump that has been maintained correctly will usually achieve a vacuum of 1000 microns quite quickly, hence the reason that triple evacuation is preferred. This method is the most common and is used extensively throughout the industry, especially in the domestic area. The use of dry nitrogen during evacuation is to act as a "drying agent‟ to assist in the dehydration of the system.




This page was last modified on 6th June 2010 and maybe out of date with regards to its information at the time of reading this article. The information above is only intended for use a guide and should not be 100% relied upon as a substitute for official manufacturer technical advice. Quality Electrics disclaims responsibility for any damage, claim, or liability any person may incur, whether caused by negligence or otherwise, as a result of anything contained in our articles.


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