Ice Breaker: Liquid â€˜Push-Pull' Recovery Method
March 10, 2008
There are several methods that can be used to recover refrigerant from a system. The most common is the vapor recovery method, where refrigerant in its vapor state is removed from a system, condensed into a liquid and then stored in a recovery cylinder. This method can be time-consuming, especially on systems with large amounts of refrigerant.
A faster method of recovering refrigerant is to remove the refrigerant in its liquid form. One method of recovering liquid refrigerant is the “push-pull” method. This method uses a recovery machine to pressurize the system and push liquid out and into the recovery tank.
This method will speed up the recovery process. However it is a two-step process, as it cannot be used to completely recover all the refrigerant from a system. When liquid refrigerant is no longer traveling from the system, the recovery process must then be switched over to the vapor recovery method for completion.
This method is not practical for all systems. If any of the following conditions are present, the liquid “push-pull” method should not be used:
• The equipment contains less than 10 pounds of refrigerant.
• The equipment is a heat pump or other system with refrigerant flow that would prevent a technician from isolating the liquid.
• The equipment has an accumulator between the service ports used in the liquid recovery process.
• Liquid refrigerant migration has occurred and the location of the liquid is unknown.
• The refrigerant tubing design on the equipment does not allow for a solid column of liquid refrigerant to be formed.
USING THE METHODTo use the “push-pull” method always follow the instructions provided by the recovery system manufacturer. Before setting up the recovery equipment, make sure the equipment (recovery machine, refrigerant hoses and recovery cylinder) can handle the pressures associated with the refrigerant being recovered. Check the condition of the recovery equipment to make sure there are no obvious defects. Also make sure to wear the appropriate personal safety equipment for proper eye and hand protection.
In a typical setup using the push-pull method to recover liquid refrigerant from a system, the manifold gauge is connected similar to that of the vapor recovery method. The low-side hose is connected to the low side of the system and the high-side hose is connected to the high side of the system.
This hookup may slightly differ depending on the service valves available and the type of system to be recovered. A refrigerant hose is connected from the liquid side of the system directly to the liquid side of the recovery tank. Connected into this line is a filter/drier and liquid line sight glass. A refrigerant hose is connected from the vapor side of the recovery tank to the inlet of the recovery machine.
The outlet of the recovery machine is connected to the transfer hose of the refrigerant manifold set. Make sure to place the recovery cylinder on a scale so its weight can be monitored during the recovery process. Do not fill any recovery cylinder to more than 80 percent of its total capacity.
Before beginning the recovery process, make sure to open the necessary manifold and system valves and purge all the refrigerant hoses to prevent atmospheric air from contaminating the re-frigerant being recovered.
Once all the refrigerant hoses have been purged, open or close the appropriate manifold and system valves which will allow the liquid refrigerant to flow from the system directly into the liquid side of the recovery cylinder and the vapor from the recovery cylinder to flow into the recovery machine and then into the system to provide the necessary pressure to push the liquid refrigerant out of the system.
Start the recovery machine and monitor the weight of the recovery cylinder and condition of the refrigerant flow through the sight glass connected to the liquid side of the recovery cylinder. When the sight glass or the refrigerant scale shows no signs of liquid refrigerant being transferred into the recovery cylinder, stop the process and switch to the vapor recovery method to complete the recovery of the refrigerant from the system.
Publication date: 03/10/2008