Level 1, Unit 3, Section 6 – 6.1 Tools & Instruments

6.1.1 — Airflow & Environmental Measurement Tools

Before diagnosing refrigerant charge or compressor issues, a technician must verify that the air system is delivering the right volume of air to the coil. These instruments measure the air and fluid conditions that surround the refrigerant circuit.

Instrument	Measures	Units	Key Maintenance Uses
Anemometer	Air velocity	FPM, m/s	Verify airflow across coils and ductwork; balance supply/return grilles; diagnose restricted airflow from dirty filters or damaged dampers. Multiply velocity × duct area = CFM or L/s.
Manometer	Static pressure	in. w.c., Pa	Measure duct static pressure to evaluate fan performance; check pressure drop across filters, coils, and dampers; verify combustion draft on applicable systems.
Psychrometer	Wet-bulb & dry-bulb temperature	°F, °C	Determine relative humidity, enthalpy, and moisture content of supply and return air; verify sensible and latent cooling capacity; identify insufficient airflow or incorrect charge.
Hygrometer	Relative humidity	% RH	Verify comfort conditions; identify over- or under-dehumidification; support mould risk assessment from poor humidity control.
Thermometer	Temperature (air, surface, fluid)	°F, °C	Measure supply/return air temperature split; measure refrigerant line surface temperatures for superheat and subcooling; check fluid temperatures in hydronic systems.
Hydrometer	Specific gravity of liquid	Relative to water = 1.0	Check glycol/antifreeze concentration; verify corrosion inhibitor levels in closed-loop hydronic systems.
Refractometer	Refractive index of liquid	% concentration	Measure glycol or brine solution concentration using a small sample. More accurate and field-friendly than a hydrometer. Used for chilled water and brine freeze-protection checks.
Tachometer	Rotational speed	RPM	Confirm fan and motor speeds match design values; evaluate belt and pulley adjustments after maintenance; diagnose slipping belts or incorrect VFD settings.

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Worked Example — Using an Anemometer to Diagnose Low Airflow

A technician receives a complaint that a split-system A/C is not keeping up on hot days. Before connecting gauges, they measure airflow at the return air grille using a vane anemometer:

Grille dimensions: 24″ × 12″ = 2.0 ft² (0.186 m²)
Measured average velocity: 320 FPM (1.63 m/s)
Calculated flow: 320 × 2.0 = 640 CFM
Design requirement for a 2-ton system: 800 CFM (400 CFM/ton)

The system is delivering only 80% of design airflow — enough to suspect a dirty filter or blocked return. The technician checks and finds a clogged 1″ filter that has not been changed in 6 months. After replacing the filter, airflow returns to 810 CFM and suction pressure rises 5 psig, confirming the airflow restriction (not a refrigerant charge problem) was responsible for the low-capacity complaint.

6.1.2 — Electrical Meters & Test Instruments

Electrical testing is central to every maintenance visit. A technician who skips electrical checks is leaving the most common cause of component failures undetected.

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Multimeter (Electrical Meter)

Measures voltage, current, and resistance in a single instrument. Essential for verifying supply voltages, checking control circuit voltages, testing fuse and switch continuity, and confirming correct polarity and phase presence.

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Clamp-On Ammeter

Measures current draw without breaking the circuit. Clamp around a single conductor to read amps. Used to compare motor and compressor running current to nameplate FLA, identify overload conditions, and detect unbalanced phase currents on three-phase equipment.

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Insulation Tester (Megohmmeter)

Applies 500–1000 V DC to measure insulation resistance in megohms. Used during scheduled maintenance on motors and compressors to identify deteriorated winding insulation before it causes shorts or ground faults. A reading below 1 MΩ is generally a concern; below 0.5 MΩ typically requires action.

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Ohmmeter

Measures resistance in ohms with the circuit de-energised. Used to check motor winding continuity, verify thermistor and RTD sensor resistance, confirm contactor and relay operation (closed = near zero, open = infinite), and test solenoid coil resistance.

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Phase Rotation Meter

Identifies whether the three-phase supply is ABC (clockwise) or CBA (counter-clockwise). Must be checked after any wiring change, equipment replacement, or reconnection. Incorrect phase rotation causes motors to run backwards — scroll compressors are destroyed in seconds if rotated the wrong way.

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Voltmeter

Measures voltage across two points. Confirms correct supply voltage at disconnects and equipment terminals, verifies low-voltage control circuits (typically 24 V), and diagnoses voltage drop in long conductor runs or undersized wire.

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Always verify the circuit is de-energised before using an ohmmeter or megohmmeter

Resistance measurements require the circuit to be completely de-energised and isolated. Taking resistance readings on live circuits damages the meter and can cause serious injury. Megohmmeter testing applies its own high voltage to the winding — other components must be disconnected first to prevent damage.

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Worked Example — Diagnosing a Compressor That Won’t Start

A single-phase 240 V compressor fails to start. The technician follows a systematic electrical test sequence:

Voltmeter at the disconnect: 241 V confirmed — supply voltage is correct.
Voltmeter at the compressor terminals during attempted start: 238 V — no significant voltage drop, so wiring is acceptable.
Ohmmeter (circuit de-energised): compressor common-to-run = 3.2 Ω, common-to-start = 5.7 Ω — windings intact, no open circuit.
Capacitor tester: start capacitor reads 82 µF vs. rated 108 µF (24% low) — defective start capacitor identified.
Capacitor replaced with correct rating; compressor starts and draws rated FLA.

6.1.3 — Pressure & Refrigerant Instruments

Refrigerant pressure and vacuum measurements provide the most direct window into cycle performance. These instruments are used on every service call.

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Compound Gauge (Low Side)

Reads both positive pressure (psig) and vacuum (in. Hg) on a single dial. Connected to the suction service valve or low-side Schrader port. Displays suction pressure for superheat calculations and refrigerant condition assessment.

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High-Pressure Gauge

Reads positive pressure only on the high side. Connected to the discharge or liquid service valve. Displays condensing pressure for subcooling calculations and condenser performance assessment.

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Digital Manifold Set

Electronic version of the traditional manifold gauge set. Provides digital pressure readings, built-in P–T charts for dozens of refrigerants, automatic superheat and subcooling calculations, and data logging. Reduces calculation errors and speeds up diagnosis significantly.

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Micron Gauge (Vacuum Gauge)

Measures deep vacuum in microns (1 micron = 1/1000 of a millimetre of mercury). Used during system evacuation to confirm the system has reached an acceptable vacuum level (≤500 microns is typical for moisture-free work; ≤300 microns for critical systems). Also used for vacuum decay testing to detect leaks and verify system integrity before charging.

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Manifold gauge hoses add refrigerant to the system — minimise use

Every time a manifold gauge set is connected and disconnected, a small volume of refrigerant is trapped in the hoses and released. On modern low-charge systems this matters. Always use hoses with depressor pins and low-loss fittings, minimise the time gauges are connected to a charged system, and remove gauges promptly after readings are taken.

6.1.4 — Hand Tools for Basic Maintenance

Measuring instruments tell you what is wrong. Hand tools fix it. A complete service kit for 313A/313D maintenance work includes:

Mechanical & Piping Tools

Screwdrivers and nut drivers (panel fasteners, terminal screws)
Adjustable and combination wrenches (piping, flare fittings)
Hex keys / Allen keys (set screws on pulleys, dampers, motor mounts)
Tubing cutter (clean cuts on copper and aluminium lines)
Flaring tool (field fabrication of flare fittings)
Tube bender (routing replacement tubing without kinks)
Straightedge or laser alignment tool (pulley alignment)

Electrical & General Tools

Wire strippers and crimping tool (field wiring, terminal connections)
Pliers — needle-nose and lineman’s (wiring, component handling)
Cordless drill / driver (panel removal, bracket installation)
Flashlight or headlamp (equipment rooms, tight spaces)
Service valve wrench (opening and closing Schrader cores)
Refrigerant recovery/charging scale (accurate weight-based charging)
Nitrogen regulator and hose (pressure testing, purging during brazing)

6.1.5 — Choosing the Right Tool for the Task

A technician arriving on a maintenance call needs to know which instruments to reach for first. This decision tree summarises the most common situations:

Complaint or Task	First Instrument	Why
System not cooling adequately	Anemometer + thermometer	Verify airflow and temperature split before connecting gauges. Airflow problems mimic low-charge symptoms.
High energy bills	Clamp-on ammeter	Measure running current on compressor and fans. Compare to FLA. High current = component stress or dirty coils.
Compressor won’t start	Voltmeter then ohmmeter	Confirm voltage present, then check capacitor and winding resistance before condemning compressor.
Humid space despite A/C running	Psychrometer	Measure supply and return air wet-bulb and dry-bulb. Calculate latent capacity. Verify correct airflow and refrigerant charge.
Pressure gauge readings abnormally high	Thermometer + manifold gauges	Compare condensing pressure to P–T chart expected value. A higher-than-expected discharge pressure vs. ambient temperature suggests non-condensables or dirty condenser.
Motor runs hot or trips overload	Clamp-on ammeter + phase rotation meter	Check current draw and phase balance. An overloaded or reverse-rotating motor trips overloads within seconds of start.
After replacing a motor or compressor	Phase rotation meter	Always verify phase rotation before energising. Incorrect rotation can destroy a scroll compressor in under 30 seconds.
Scheduled system evacuation	Micron gauge	Manifold gauges cannot resolve deep vacuum. A micron gauge confirms acceptable evacuation depth and vacuum decay testing detects residual leaks.