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pre commission office air conditioning

Every office air conditioning installation requires careful detail and attention given to the pre commissioning works prior to a run test.

During a commercial office air conditioning installation a lot of brazing will have taken place. In addition, there will be lots of flare connections and the fitting of pipe branch work with VRV installations.

Even the most experienced air conditioning specialists may have a leaking fitting or two after a large commercial air conditioning installation. Furthermore, leaks can develop over time on a system due to vibrations or the natural heat expansion on the copper. It is therefore equally important to make sure the pipe work vibrations are kept to a minimum with the use of the correct types of support brackets.

Pressure testing

Air conditioning systems run on a very high pressure gas, r410a. It was brought in circulation due to its better ozone depleting properties. However, its operational pressure is more than double that of the previous used air conditioning gases, R407c and R22. R410a is used for commercial and residential air conditioning installation. It has discharge high side pressures of over 35bar in operation. It is therefore necessary to pressure test R410a systems with up to 40bar of nitrogen. Applying this pressure needs to be done gradually over a short time period while checking for leaks. Never apply 40bar of pressure directly from a nitrogen gauge into a system. Even though a R410a system has the strength to maintain this pressure, a sudden surge may blow a slightly less tolerant pressure sensor or switch. There have been instances where the coil on an internal wall mounted air conditioning unit has blown on the surge of pressure.


Oxygen free nitrogen is the name of the gas that commissioning air conditioning installers will need to use. The key in the name is its “oxygen" free which means it doesn’t carry moisture into your system pipe work. Oxygen carries moisture vapour and would be lethal to an efficient cooling system design. This moisture would condense into water within the system and destroy the compressor after a short time. Therefore, you cannot in any circumstance use an air compressor to pressure test air conditioning system pipe work. After a 24hr or longer pressure test, depending on the size of the system, the nitrogen needs to be removed. Trapped nitrogen in a system can also cause damage to air conditioning SystemsNitrogen will not compress. When left in the system it will mix with the refrigerant gas. When the compressor operates it will not be able to compress the nitrogen. The nitrogen will cause the head pressure to keep rising until the system trips on a High sensor alert.

Removing the OFN and all moisture contaminates

After confirming a successful pressure test it is necessary to slowly let all the nitrogen out. As it has zero ozone deleting properties it is safe and legal to vent this to the atmosphere. Once you’re pressure is down to below 1bar with nitrogen you can attach a vacuum pump. The only way to successfully dry out the office  air conditioning system is with the use of the faithful vac pump. The vac pump must have a fresh oil change before every use and be used inline with a torr gauge. The torr gauge gives a negative pressure reading of the level of vacuum reached. This gives a measure of the removal of all moisture removed. A 1-2 torr reading the generally the level you would have achieved an adequate vacuum. Older commercial air conditioning systems that have had multiple compressor changes will take time to vacuum. This is because of the build up of moisture contaminates from continually breaking into the refrigerant system.

What next for your office air conditioning?

An office air conditioning system with multiple existing pre commissioning works and system parts changed, will need oil changes and liquid line filter driers fitted. This is the case for parts changed that require breaking into the refrigerant system. This does not apply to electrical parts changes such as fan motor and relays. Bespoke wine cellar cooling systems need particular attention paid to regular liquid line filter drier changes. Refrigeration systems have a longer running time and suffer more leaks than split home air conditioning systems. This is particularly due to compressor vibrations and heat build up in the condenser.

Triple vac

This is the process of sending nitrogen into a refrigeration circuit up to about 1bar. Attach the vac pump with the 1 bar of pressure in there and run for a short period (15-30mins). Repeat this process three times, cycling between OFN charging to 1 bar and evacuating the system. This process can sometimes be used in preference to a “deep vac" in achieving your torr readings. The low pressure charging of the OFN pics up moisture contaminates that you are then drawing out of the system quickly. The water acts as the medium that collects the dirt and then is through into the sink. Triple vac’ing acts the same where by the OFN is the medium collecting moisture deeper down in the refrigeration circuit. Every time the vac pump is shortly applied after it is therefore dragging the  moisture out with the OFN.

Refrigerant Gauges and hoses 

A good, potentially new set of gauges are what you should be using prior to any pre commissioning works. Gases pass through them. Furthermore, all the contaminates will pass through gauges and hoses. Contaminated oil and moisture will sit in the gauges and hoses. Therefore, make sure to blow through the gauges with OFN heavily before connecting them to any HVAC system.

Video Guidelines

In our video attached we have demonstrated a small domestic air conditioning pre commissioning exercise. This is a guide for trainees and professionals qualified in the handling of refrigerant gases. Experienced air conditioning contractors in London will carry an “FGAS’ qualification. For help with office air conditioning installation in London contact us directly for all your climate control installation commissioning needs or use below link.