Reefer Servicing — Pump-Down, Charging, Leaks, Valves, Defrost & Faults
Pump down before you open anything, charge by weight, and read every fault from its gauges and glass.
Key Principles at a Glance 6 points
- Pump down first: close the receiver outlet, let the compressor pack the charge into the condenser on LP trip — then work on an empty section.
- Air betrays itself by a rising HP gauge at constant seawater temperature; vent it from the condenser top where it stratifies above liquid.
- Charge by weight through the liquid side with the cylinder upright on its liquid valve, drier in circuit, sight glass watched, quantity logged.
- Valve health is measurable: 1 bar discharge fall in 5 minutes condemns the discharge valve; failure to hold 0.4 bar vacuum condemns suction.
- Defrost before frost passes 1/4 inch — ice insulates the coil, chokes airflow and sends liquid back to the compressor.
- Every fault reads through the same witnesses: suction and discharge pressures, sight glass, ammeter, room temperature and run time.
1. Safe Isolation Always Starts With Pump-Down
One line first: pack the refrigerant into the condenser before touching anything — an empty work section cannot burn, freeze or asphyxiate you. Closing the condenser-outlet (receiver) liquid valve and letting the running compressor pull the charge forward until LP trip is the isolation that every oil, strainer, charging and leak job below assumes.
Why water keeps running: the condenser's cooling water continues about 30 minutes after the stop so the parked charge settles instead of sitting on hot spots. For oil and strainer work this same pump-down empties the crankcase side — see Reefer Oil Control, Separators, TEV & Safety Cutouts.
2. Prove the Air Out — Stratification Does the Test
One line first: air will not condense, so it floats above the liquid and steals condenser surface — the HP gauge climbing at steady seawater temperature is its signature. The test needs equilibrium: outlet shut, compressor tripped on LP, seawater circulating for hours, then one reading compared against the earlier one.
Judge the HP reading only at equilibrium — circulating seawater, settled charge, same condensing temperature as before. A needle that jumps indefinitely under load is the running-plant version of the same fault (see the fault table).
3. Charge by Weight, Repair Leaks Properly
One line first: the scale is the charge record — weigh the cylinder before and after, and the difference is the legal quantity in the logbook. Charging goes through the high-side liquid charging valve with the cylinder upright on its liquid valve, the drier in circuit, and the compressor on manual.
Put the drier in circuit (inlet/outlet open, bypass shut) and weigh the cylinder — because the before/after difference is the charge record.
Pump down, connect to the liquid side with the cylinder upright, crack the valve to blow hose air out, then tighten — because hose air becomes system air.
Open charging and cylinder valves, run the compressor on manual, watch the sight glass fill; then purge residual air at the condenser vent, restore the drier bypass, reopen the receiver outlet and prove efficiency for 20 minutes against receiver level.
Copper-pipe leaks: the permanent cure is renewing the section; the at-sea repair is a ferrule joint — pump down, cut with a pipe cutter, fit female pieces with thread tape, tighten, reopen and prove. Fast-cure plastic-steel putty buys hours only, never a voyage.
4. Two Valve Tests, Two Numbers
One line first: valves are proved by the vacuum they hold, not by how they look — one number condemns the discharge valve, one the suction. Both tests start from the same place: charge collected to LP trip.
Discharge valve — 1 bar / 5 min
Pump down to LP trip, slam suction and discharge shut, watch both gauges. Discharge falling ~1 bar in five minutes while suction climbs means the discharge valve leaks back.
Suction valve — 0.4 bar vacuum
Run on manual, ease the suction valve shut (slowly — no oil foaming). Holding 0.4 bar vacuum or better proves the suction valves seat; failure to pull down condemns them.
5. Defrost Before ¼ Inch — Five Systems, Right Temperatures
One line first: frost is triple damage — insulation on the coil, a choke on airflow, and liquid carried back to the compressor — so defrost on thickness, not on convenience. Start before build-up passes ¼ inch, by whichever system is fitted.
Two plants of equal capacity sail together so one always covers maintenance; room thermostats drive solenoid valves per space, and a timer defrosts evaporators on schedule while parameters are logged for trend-watching. Cold-room coils also defrost by plant stop with manual watering, circulating hot gas, or electric heaters.
6. The Fault Table — Indication, Cause, Action
One line first: every fault below confesses through the same five witnesses — suction and discharge pressures, sight glass, ammeter, room temperature and run time — so read them together, never singly.
| Fault | Indications | Causes → Action |
|---|---|---|
| Undercharge | Hot compressor, high suction superheat, low suction and discharge, big vapour bubbles in sight glass, low condenser readings, low amps, warm rooms, extended running | Shaft-seal/flange/gland leaks, blocked TEV strainer, choked filter/drier/evaporator → find and fix leaks, clean strainer, filter and drier, recharge. |
| Overcharge | High condenser liquid level and gauge, lost condensing surface, both pressures high, HP switch trips | Excess gas (or air mimicking it, or iced regulator) → draw charge into a cylinder via the liquid-line valve, purge air, defrost regulator. |
| Moisture | Mimics undercharge, freezes at TEV, corrodes, breaks oil down | Air ingress → silica-gel renewal for traces; full reclaim plus vacuum-pump dehydration for floods. |
| Air | Overheating compressor, high discharge at normal condensing temperature, bubbles in glass, jumping HP needle, long runs, lost capacity | Charging ingress or sub-atmospheric suction leaks → collect gas in condenser with water on, vent the top, shut purge valve, check level, recharge, restart guarded. |
| Oil logging | Rooms not pulling down, frosted suction line, falling crankcase level, blocked-level fall, extended running, heavy starting current | Dead separator, blocked return, worn rings/liner → prove separator, clean drier, drain evaporator coils, warm pipes; for oil in coils raise differentials and strip excess frost. |
| Flooding back | Liquid at suction, iced evaporator, iced suction, high suction pressure | Faulty/mis-set TEV, leaking solenoid, overcharge, abnormal TEV operation → reset or renew valve, correct charge, fix solenoid. |
| Iced evaporator coil | Poor heat transfer, weak airflow, icing | Too-low setting → raise coil temperature via TEV/sensor; undersized coil → fit larger; dead defrost → restore timed defrost. |
| Start-then-stop | Cuts out seconds after starting | LP cutout (shut valves, low charge, defective cutout), oil-pressure cutout (low/foamed oil, defective), hyperactive defrost timer, overload trips → prove each in turn, refill/renew oil, repair timer. |
| Defective discharge valve | Continuous running, poor cooling, noisy, high running suction, low running discharge, fast suction rise after shutdown, warm head | Worn/leaking discharge valve → overhaul valves (see valve tests). |
| Choked TEV | Starved evaporator, high superheat, HP climbing toward trip | Dirt or frozen moisture → clean valve and strainer, renew dehydrator. |