Charging & Circuit Service

This is where refrigeration becomes a trade: weigh-in charging, evacuation, metering devices, and leak detection. These are the hands-on skills that make or break a refrigeration tech. The discipline here is non-negotiable — a system charged to guess fails in six months; a system charged to spec lasts.

Why it matters: an inadequate evacuation leaves moisture in the system, which reacts with the refrigerant and oil to form acids that destroy the compressor.

Weigh-in charging is the only reliable way to set a charge:

1. Connect a scale to the liquid line.
2. Weigh the system before and after adding refrigerant.
3. Add exactly the amount the manufacturer specifies.
4. Verify the superheat and subcooling are within spec.

Evacuation is the step before charging — you pull a vacuum to remove air and moisture before introducing refrigerant. The rule: evacuate to 500 microns or better, hold for 30 minutes, and verify the hold before charging.

A TXV (thermodynamic expansion valve) meters refrigerant flow based on the superheat at the evaporator outlet. It opens and closes automatically as the load changes. A capillary tube is a fixed-length, fixed-diameter tube that meters flow by restriction — it cannot adapt to changing load.

• TXV — the correct choice for variable-load applications (a walk-in that is sometimes full and sometimes empty).
• Capillary — acceptable for constant-load applications (a single cabin AC).

A refrigerant leak in a marine system is almost always at a joint, not in a component. Check first:

1. Compressor suction and discharge ports.
2. Condenser connections.
3. The expansion device.
4. Evaporator connections.

Use an electronic leak detector at each joint. If you find a leak, repair it before you recharge. A system that has leaked and been recharged without repairing the leak is a system that will leak again.