Confirm the system is set to cool and is actually running (compressor and both fans on), and note ambient conditions before you touch anything. Required before proceeding to any reading below.

Visually check filter condition, coil cleanliness/icing, and that supply and return registers are open and unblocked.

Take return and supply air temperatures through the check. A high split points to low airflow; a low split points to charge or metering. A healthy split is roughly 8.5–12.5 °C at ~50% indoor RH — the tool adjusts the band for humidity.

If the split points to charge, hook up gauges. The tool gives a deterministic verdict: undercharge, overcharge, restriction or airflow.

Cross-check any suspicious gauge reading against saturation pressure for the refrigerant before adding or recovering gas.

If refrigerant is added or recovered in Australia, record the movement before leaving site.

Is the compressor actually running, or is the unit in defrost? Check the controller setpoint and differential, and compare its probe reading against your own thermometer — a drifted or badly-placed probe fakes a “not cooling” call.

Look for an iced-up coil, dead evaporator fans, or product stacked against the airflow. An iced coil means a defrost problem (heater, timer, termination, drain) or door/infiltration load — fix that first; charge readings on an iced coil are meaningless.

Dirty condenser coil, failed condenser fan, or a plant room running hot — all push head pressure up and capacity down. Clean the coil and confirm fan operation before touching refrigerant.

With coils clean and fans running, take superheat and subcooling at the room's actual evaporating temperature. Wrong superheat (TXV drifted, bulb loose) starves or floods the coil even with a correct charge. As a guide: refrigeration coils typically run 4–8 K superheat, with the evaporator about 6–10 K below room temperature (freezers 5–8 K).

Cross-check gauge readings against saturation pressure at the room's evap temp. Low suction + low subcooling → charge or leak. High subcooling + starved evap → restriction (drier/TXV). Low head AND high suction with low amps → compressor not pumping.

If the plant checks out but can't keep up, the room load may have outgrown it — verify with the coolroom heat load. Record any refrigerant added or recovered before leaving site.

Lock off before opening the panel. Find the wiring diagram (panel door or lid), identify the control voltage (24 V / 240 V) and note the order of controls in the safety chain before probing anything.

Confirm the control voltage is present — transformer output, control fuse, and any plug/terminal connections. No control voltage explains everything downstream; fix that first.

Work along the chain — HP switch, LP switch, overloads, klixon, defrost termination, door/limit switches — checking continuity or voltage through each in order until you find the one that's open.

Pressure control: compare its cut-in / cut-out settings against the actual gauge reading and saturation data — is it open because it's faulty, or because the pressure really is out of range? Thermostat: compare its switch point against a trusted probe.

With the chain closed, does the contactor pull in cleanly? Chattering points to control-voltage drop or a failing coil; burnt or pitted contacts drop voltage to the compressor. Measure coil resistance if it's dead.

Run the unit, confirm amps against nameplate, and watch a full cycle to prove it isn't short-cycling. Record any control settings you changed (cut-in/cut-out, differential) on the job.

Note the controller error code or count the indoor LED blinks before touching anything, and look it up — service manual, lid sticker or manufacturer app. The code usually names the exact sensor or circuit, and it clears when you cut power.

Isolate, then confirm 240 V at both units, the PCB fuse, and the transformer output. Check the interconnect / comms wiring for continuity, correct polarity and tight terminals — a comms fault mimics a dead outdoor board.

Thermistors: unplug and measure resistance against the manual's temperature chart (many are ~10 kΩ at 25 °C, falling as temperature rises). Quick field check: two like sensors at the same temperature should read nearly the same — an open, shorted or drifted one stands out.

With a demand present, verify each PCB relay output actually switches — fan speeds, reversing valve coil, compressor call. Separate “board not calling” from “load not responding” before condemning either.

Inverter DC bus capacitors hold lethal charge after isolation — wait and measure the bus down before touching. Follow the manufacturer's procedure for IPM and compressor winding checks; don't meg an inverter compressor like a fixed-speed one.

Power up, run a full cycle, confirm amps against nameplate and that the fault doesn't return. Record the original fault code and what fixed it — it's gold for the next tech.

Isolate, lock off and discharge capacitors before touching anything. Required before any reading below — this is a live-electrical fault call.

Measure the capacitor out of circuit and check it against its rated µF.

With a call for cooling present, is the contactor coil getting its control voltage (24 V or 240 V) and pulling in cleanly? No coil voltage = the fault is on the control side, not the compressor — switch to the control fault-finding procedure. Pulled in but no power through = burnt or pitted contacts.

If it starts but trips, confirm supply voltage under load, then clamp on and enter running amps against nameplate RLA/LRA — the tool flags locked-rotor, overload and light-load patterns.

On 3-phase gear, enter all three leg voltages and currents — imbalance over 2% voltage or 10% current is a supply/winding problem, not a charge problem.

If capacitor, supply, contactor and phase balance all check out, the fault is more likely mechanical. Verify head pressure against saturation pressure before condemning the compressor and quoting a replacement.

Measure length, width and ceiling height, note building type, occupants, lighting and equipment heat, then enter it all in the calculator.

Set the site location so the tool uses the correct design temperature — or override it manually for unusual sites.

Enter model numbers, capacity and refrigerant in the same tool; it compares estimated load against existing capacity and flags undersizing.

If the site is humid or ventilation-heavy, check the latent load before locking in capacity. Skip this step for a straightforward sensible-load job.

Generate the supplier email / PDF report from the Heat Load result to hand off.

Measure length, width and height, and confirm the target holding temperature (coolroom or freezer) before entering anything.

Panel type/thickness, door count/size/glass, product turnover and infiltration — retail door traffic is often the biggest hidden load, so use real numbers, not guesses.

Enter everything from the previous two steps into the calculator using the Coolroom or Freezer mode preset, then read off the calculated load.

If the existing plant can't hold temperature, check the charge with Superheat & Subcooling and confirm saturation pressures on the PT Chart at the room's actual evaporating temperature — not its nominal kW.

Any refrigerant handled during rectification, or legal paperwork required for the job, must be recorded.