In this short podcast episode, Roman Baugh takes over the HVAC School podcast to answer a listener-submitted question about VRF (or VRV) system evacuation.
Evacuation is a critical step of making repairs on VRF systems, which are very diverse and versatile but require a high level of understanding. VRF systems have multiple indoor units per outdoor unit, and they achieve that with the help of several components and accessories down the refrigerant line that can pose issues in evacuation and pressure testing.
In heat recovery units, some manufacturers use solenoid valves (or even electronic expansion valves) in branch selector boxes or branch collector boxes. These valves act as little traffic guards, and the system needs to be put in its refrigerant recovery or vacuuming mode. If not, then you won't be able to evacuate all of the refrigerant and non-condensables from the system. Even if the system passes a decay test, contamination is a major concern when the system starts up and the valves open (due to nitrogen and oxygen mixing with pure refrigerant being put into the system).
You can trust and verify that the system is in its proper operating mode at the thermostat to ensure that the valves are open 100% and ready for evacuation or pressure testing. Failure to do so not only poses a contamination risk but likely won't maintain its pressure during the pressure test. Assumption or trust alone is not enough.
Heat pumps only have two lines, and the vacuum pulls from both sides of the valve. There's less of an issue because there are no branch selector or collector boxes, but it's still good to ensure that the valves are responding and communicating.
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