Evacuating a refrigeration system can be a very time-consuming task. It takes time for a vacuum pump to sufficiently reduce the system’s internal pressure to allow the water vapor contained within to be reduced to acceptable levels. Some of the factors that influence the speed of this process include:
• Internal volume of the system;
• Amount of moisture contained within the system;
• Ambient temperature present;
• Amount of internal system restrictions;
• Amount of external restrictions between the system and the vacuum pump; and
• Size of the vacuum pump.
A technician has no control over many of these factors, but there are some areas in which he can help speed up this process.
Technicians should always set up their vacuum pump so it pulls a vacuum from both sides of the system. Pulling a vacuum from only one side greatly increases the time for proper system evacuation. The connecting line between the vacuum pump and the system should be one that is as short as possible and has the largest possible internal diameter.
Many technicians use a standard ¼-inch refrigerant hose during the evacuation process. They should instead be using a 3/8-inch refrigerant hose that is rated for vacuum use or use a section of copper tubing. This will help to reduce the restriction between the vacuum pump and the system.
Schrader valves offer an unneeded restriction during the evacuation process. Systems with service hoses that are connected via a Schrader valve should use a valve core remover that allows the cores to be removed without detaching the hoses from the system. Once the evacuation process is complete, the valve cores can be inserted back into the Schrader valves without losing the vacuum.
Technicians should always use clean oil in their vacuum pumps. This ensures the pump is able to reduce the system’s pressure to an acceptable micron level. Using containment oil will hinder the vacuum pump’s ability to pull a deep vacuum. Technicians can waste valuable time waiting for the system pressure to reach an acceptable level - but is unable to do so because of containment oil. Technicians should always perform a blank-off test before opening a vacuum pump to a system. This will ensure that the vacuum pump can obtain the required vacuum levels.
On larger systems, a technician can use two vacuum pumps. Attach one to the system’s low side and the other to the system’s high side. This will help to reduce the effect of internal restrictions present and speed up the process.
Also, do not forget to use a quality vacuum gauge. This allows a technician to operate a vacuum pump only as long as is required to properly dehydrate the system. Do not base the evacuation process on time. Operating a vacuum on a system for 30 minutes and assuming the system is completely evacuated is not an accurate method and should not be done. That is just guessing at the process and is not very professional.
Using these new practices will help to ensure that a complete evacuation is performed in a timely fashion and will help to make good technicians better technicians.
Ice Breaker: Evacuation Speed Up
October 6, 2008