When the vacuum reaches -

66 Amp rating of this transformer

If the circuit remains open while the system is cool and the button is depressed

or if the internal relay fails to switch the reversing valve and outdoor fan during a forced defrost

Since this is a normally closed (NC) switch

Emerson Alco 806730 Ball Valve When the vacuum reaches -The Emerson Alco 806730 is a high performance 1 4" ODF sweat refrigeration ball valve engineered for critical isolation in HVACR systems. Operating as a direct replacement for the legacy 064383 model, this BVE 014 manual shut off valve is designed for high pressure applications with a 650 PSI maximum working pressure. The full port design ensures minimal pressure drop and maximum flow capacity, making it essential for liquid, suction, and hot gas line