In order to admit the initial refrigerant charge into the circuit, or add further if required, a charging connection is required. The safest place to introduce refrigerant is ahead of the expansion valve, which can then control the flow and prevent liquid reaching the compressor. The usual position is in a branch of the liquid line, and it is fitted with a shut-off valve and a suitable connector with a sealing cap or flange. A valve is needed in the main liquid line, just upstream from the branch and within reach.
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