Push-Pull Recovery Process
In the push-pull method of recovery, the recovery unit “pulls” vapor from the recovery cylinder and produces high-pressure discharge gas that “pushes” liquid out of the HVAC system and back into the recovery cylinder. Push-pull quickly removes liquid refrigerant, but it’s a two-step process: Once all the liquid is removed in the first step, you have to change hose connections to recover the vapor.
Generally speaking, you’d only use the push-pull method if you have more than 10 pounds of refrigerant in the system. Push-pull is not recommended if the system is a heat pump or is one with a reversing valve. Nor would you use it if the system won’t allow a solid column of liquid to form, or if the system has an accumulator.
Because of the different set up, you’ll need some extra equipment when performing a push-pull recovery: an additional hose, a recovery cylinder with no more than five pounds of refrigerant and a sight glass rated for the pressure of the refrigerant you’re using.
Once you have everything you need, you are ready to get started. Let’s go through the process using the YELLOW JACKET RecoverXLT Refrigerant Recovery Machine.
- Turn off the power to the system you’re servicing.
- Connect a hose from the DISCHARGE port of the recovery unit to the vapor side of the HVAC system.
- Connect another hose from the liquid side of the HVAC system to the sight glass and on to the liquid side of the recovery tank.
- Connect a hose from the vapor side of the recovery tank to the SUCTION port of the recovery unit.
- Once all connections are hooked up, purge the hoses of non-condensables before starting recovery.
- Open the valves on the recovery tank.
- Turn the selector valve on your recovery unit to VAPOR, and turn the recovery unit on.
- While recovery is in progress, closely watch the sight glass. When the passing liquid is no longer visible through the sight glass, or when the scale reading stops going up, the push-pull method of recovery is complete.
- Close the VAPOR valve on the recovery tank and let the recovery unit run until the lamp indicates “recovery complete.” When recovery is complete, turn the system switch “off” and turn the selector valve clockwise to “off.”
- Turn the system switch on and turn the selector valve to PURGE. When the unit again shuts down and the lamp indicates “recovery complete,” the purge is complete.
- Turn your recovery unit off.
- Close the LIQUID valve on your recovery tank.
- Reconnect your hoses as in a standard vapor recovery.
- Turn the selector valve to VAPOR and run the vapor recovery process, continuing until the unit shuts off.
- Purge once more before you begin servicing your HVAC system. This final purge clears the recovery unit of refrigerant, reducing the risk of cross contamination and prolonging the life of your equipment. You MUST purge after every service!