After the refrigerant has been recovered, leaks repaired if necessary, the system ideally should undergo a dehydration evacuation prior to recharging with refrigerant. As shown in the illustration, besides the vacuum pump suction manifold isolation valve being opened, what would be the proper valve positions to accomplish and prove the evacuation? Illustration GS-RA-51
• Refrigeration service valves (front seated, back seated, mid-position) and how they affect flow paths • Purpose of a vacuum pump and how to connect it to both high and low sides of the system • How to prove (verify) that the system is actually holding a vacuum after isolation
• Think about which valve positions will allow the vacuum pump to pull on the entire system (both high and low side), not just one line or the gauge hoses. • Consider how you can isolate the vacuum pump and manifold from the system after evacuation so you can see if the system holds vacuum on the gauges. • For each answer, trace the refrigerant (or air) flow path from the system, through valves 1, 2, and 3, into the manifold set and vacuum pump—ask yourself: can I both evacuate and then isolate to prove tightness?
• Verify what front seated, back seated, and mid-position mean for a service valve: which ports are open/blocked in each position. • Check that the chosen valve positions allow the vacuum pump to communicate with both sides of the system during evacuation. • Check that, once evacuation is complete, you can close the correct hand valves on the manifold to isolate the pump and watch the system vacuum for a rise, without losing the vacuum you just pulled.
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