HVAC and Refrigeration Circuit Evacuation Best Practices

One of the most important procedures in the manufacturing of HVAC and refrigeration units is the evacuation (or degassing) of circuits. The procedure of evacuating circuits can also be one of the bottlenecks of the manufacturing process because of the time needed to ensure all moisture and unwanted molecules, are successfully evacuated from the system.

One important concept to understand about evacuation procedures of HVAC or refrigeration units is a bout how the molecules leave the system. Just because vacuum pumps are used in the system, does not mean that the molecules are being sucked/vacuumed out of the system like a household vacuum sucking up dust. The vacuum pumps lower the pressure in the system making water turn to vapor at room temperature inside the circuit. While doing this, the vacuum pumps create a negative atmospheric pressure outside the circuit which causes the molecules bouncing around inside (in a crowded space) to escape the system moving into a lower pressure area (the pump). The molecules must find their way out of the system while bouncing around. Any obstacles in their way can make it harder to bounce their way out of the system.

Here is a list of the best practices to optimize your evacuation process:

  • Minimize the number of connections, orifices, valves, etc. between the vacuum pump and the circuit. These connections act as obstacles to the molecules that make it harder for them to find their way out.
  • Minimize hose lengths and maximize hose diameters. Larger hoses allow more molecules to evacuate at the same time, and a shorter length allows them to evacuate faster.
  • Reduce the use of elbows or sharp angles in the hoses. The easier the path for the molecules to escape, the quicker your evacuation times will be.
  • Connect to high and low-pressure sides. Evacuating through connections from both the high and low sides of your circuit will allow the molecules inside your system to find their way out faster.
  • Make sure your pumps are serviced regularly. Dirty pump oil can greatly reduce your evacuation performance because it will be unable to trap the moisture and other unwanted molecules coming out of your system.
  • Maximize the inside diameter of any connections. Example: If you, are evacuating through Schrader Valves, then you should remove the cores before evacuation. By removing the cores before you evacuate, you could save up to 25% of your total evacuation time.
  • Make sure your system is sealed and not leaking. A leak in your system will work against your efforts to remove any moisture or air in the system.