When charging refrigerant on the low side of a reciprocating machine with manifold gauges, what is the position of the manifold?

• A. High side backseated, low side frontseated
• B. High side frontseated, low side backseated
• C. Low side frontseated, high side backseated
• D. High side frontseated, low side backseated

Answer: (D)

The key idea is to control the flow path so refrigerant goes into the low-pressure side without letting high-pressure refrigerant travel through the high-side circuit while you’re charging.

When charging on the low side, you want the high-side path sealed off and the low-side path open to the evaporator. In the valve terminology used here, that means the high side is in the closed (frontseated) position and the low side is in the open (backseated) position. This arrangement lets refrigerant flow from the cylinder into the evaporator via the low-side hose while preventing refrigerant from pushing into the high-side circuit.