Cert III Air Conditioning & Refrigeration cheat sheet

WHS duty holders: PCBUs must ensure health and safety so far as reasonably practicable; workers must take reasonable care and follow controls; officers exercise due diligence.

Hierarchy of control, highest to lowest: eliminate, substitute, engineering controls, administrative controls, PPE - PPE is the last line of defence only.

Refrigerant exposure: use oxygen-depletion and refrigerant monitors in plant rooms; ozone-depleting and high-GWP refrigerants require leak detection, logbook records and recovery, never venting.

Recovery targets: recover refrigerant before opening any circuit; recycled refrigerant may be reused only in equipment owned by the same owner; reclaimed refrigerant must meet purity standards.

Oxygen-fuel gas (oxy-acetylene) brazing: flashback arrestors on both regulators, cylinders upright and secured, hoses inspected, fire watch during and after hot work.

Electrical safety: tag-out/lock-out before work on control circuits; test for dead with a proven tester; RCDs on portable tools; safe isolation confirmed at the point of work.

Personal exposure limits: assess noise (85 dB(A) 8-hour action level), heat, and refrigerant exposure; record atmospheric tests before entering confined plant spaces.

Pressure hazards: never trap liquid refrigerant between closed valves; fit pressure relief devices; hydrostatic test with nitrogen, not air or oxygen, and never exceed test pressure.

Environmental records: refrigerant purchase, use, recovery and disposal must be documented; leak checks are more frequent for larger charge systems.

Vapour-compression cycle sequence: evaporator absorbs heat, compressor raises pressure and temperature, condenser rejects heat, expansion device drops pressure and temperature.

Sensible heat changes temperature with no phase change; latent heat changes phase at constant temperature (latent heat of vaporisation is the dominant load in an evaporator).

Superheat = suction temperature minus evaporating (saturation) temperature; subcooling = condensing temperature minus liquid line temperature.

Pressure-temperature relationship: for a given refrigerant, saturation pressure fixes saturation temperature; use the PT chart for the specific refrigerant, never a substitute.

Refrigerant glide: zeotropic blends (e.g. R-407C) have a temperature glide, so use dew point for superheat and bubble point for subcooling calculations.

Common refrigerants: R-134a (medium temperature, GWP 1430), R-410A (high pressure, GWP 2088), R-32 (lower GWP alternative), R-744 (CO2, very high pressure, transcritical operation).

Compression ratio = absolute discharge pressure ÷ absolute suction pressure; high ratios raise discharge temperature and reduce volumetric efficiency.

Air properties: dry-bulb is sensible temperature, wet-bulb reflects evaporative cooling, dew point is where condensation begins; relative humidity is the ratio of actual to saturation vapour pressure.

Ohm's law V = I × R; power P = V × I for resistive loads; for AC use power factor: P = V × I × PF.

Single-phase motor start methods: permanent split capacitor (run capacitor only), capacitor-start capacitor-run, and positive temperature coefficient (PTC) start devices.

Three-phase supply: 400 V line-to-line, 230 V line-to-neutral in Australia; phase rotation must be correct for scroll and screw compressors or damage results.

Contactor and overload: thermal overload protects the motor; check trip class and reset; control circuit fuses protect the coil circuit, not the compressor.

Thermostat and pressure switch logic: low-pressure switch cuts out on low suction, high-pressure switch cuts out on high discharge; both are safety devices, not operating controls.

Defrost controls: time-initiated, temperature- or pressure-terminated; defrost termination sensor must be positioned to sense coil temperature, not air temperature.

Superheat control with thermostatic expansion valve: bulb clamped to suction line, insulated, and charged with the same refrigerant family as the system.

Electrical fault finding: measure voltage drop across contacts, resistance to earth, and insulation resistance (megger) before energising; compare readings to nameplate values.

Pipe sizing: suction lines sized for low pressure drop to protect capacity; liquid lines sized to avoid flashing; hot gas lines sized for velocity to carry oil.

Brazing: purge with dry nitrogen while brazing to prevent internal oxidation (scale); use silver-phosphor alloy for copper-to-copper joints.

Evacuation: triple evacuation with nitrogen breaks to below 500 microns (about 66 Pa) and hold to confirm no moisture or leaks.

Pressure testing: dry nitrogen test at the design test pressure, hold and record; never use oxygen or air on a refrigerant circuit.

Refrigerant charging: charge by weight where possible; for blends charge as liquid to avoid fractionation; verify superheat and subcooling after charging.

Airflow commissioning: measure static pressure, fan speed and air quantity; balance to design airflow; check filter pressure drop and coil face velocity.

Electrical commissioning: check supply voltage and phase sequence, motor rotation, control interlocks, and safety switch operation before full load.

Documentation at handover: as-installed drawings, commissioning records, refrigerant charge and type, and operating instructions.

Systematic diagnosis: gather symptoms, check the simplest causes first, confirm with measured superheat, subcooling, pressures and current draw before replacing parts.

High superheat with low suction pressure suggests undercharge, restricted liquid line, or a blocked/underfeeding expansion valve.

Low superheat with high suction pressure suggests overcharge or an overfeeding expansion valve; liquid floodback risks compressor damage.

High discharge pressure causes: poor condenser airflow, fouled coil, non-condensables in the circuit, or high ambient temperature.

Low discharge pressure with normal suction suggests compressor valve wear or low load; confirm with amp draw against nameplate.

Moisture indicators: sight glass colour change indicates moisture; acid test indicates oil breakdown; both point to evacuation or burnout issues.

Electrical faults: open winding, shorted winding, capacitor failure, or contactor pitting; isolate, prove dead, then test with a meter.

Repair verification: after repair, re-evacuate, recharge, and record superheat, subcooling and amp draw to confirm the fault is cleared.

Preventive maintenance scope: clean coils and filters, check refrigerant charge, inspect electrical connections, test safeties, lubricate moving parts, record readings.

Leak testing methods: electronic detector, soap bubbles, pressure decay, and UV dye; confirm the leak location and repair before recharging.

Refrigerant recovery: use recovery machines rated for the refrigerant; evacuate to the required vacuum; never mix refrigerant types in a recovery cylinder.

Decommissioning sequence: isolate electrical supply, recover refrigerant, purge with nitrogen, cap and label lines, remove oil and dispose of it as regulated waste.

Oil management: check oil level and colour; acidic or dark oil indicates overheating or moisture; oil type must match the compressor specification.

Compressor service: check winding resistance and insulation resistance, capacitor condition, and running current; record before and after values.

Records: maintenance logs, refrigerant usage records and service reports must be retained and available for audit.

Disposal: refrigerant cylinders, oil and contaminated components are regulated waste; use licensed contractors and record disposal.

Job documentation: record site, equipment model and serial, refrigerant type and charge, readings, work performed, parts used and follow-up required.

Refrigerant records must show quantity purchased, used, recovered and disposed of, with dates and equipment identifiers.

Customer communication: explain the fault in plain language, state the options (repair, replace, monitor), and confirm the scope and cost before starting work.

Safety communication: advise the customer of hazards (electrical, refrigerant, hot work) and required isolation before work begins.

Warranty and compliance: document that work meets the relevant standard and manufacturer instructions; keep records for the warranty period.

Handover: provide operating instructions, maintenance schedule and emergency contact; confirm the customer understands the controls.

Licensing: refrigerant handling requires the appropriate national refrigerant handling licence; electrical work requires a licensed electrician.

Standards and codes: work to AS/NZS 1677 (refrigerating systems), AS/NZS 5141 (air conditioning), and the relevant electrical wiring rules.

Environmental obligations: ozone-depleting substances and synthetic greenhouse gases are regulated; venting is prohibited and leak reporting thresholds apply.

Teamwork: use clear handover, tag-out coordination, and permit systems when multiple trades work on the same plant.

Housekeeping: keep work areas clear, store cylinders upright and secured, and label all containers and lines.

Incident reporting: report hazards, near misses and injuries through the site system; participate in toolbox talks and risk assessments.

Continuous improvement: review procedures after incidents, update SWMS (safe work method statements) and share lessons with the team.