Tools, Materials, and Equipment
This domain tests selection, safe use, and interpretation of the instruments and materials used on appliances. Expect questions about which meter, gauge, or tool suits a task, and what a reading actually means.
Measurement and test equipment
- DMM: choose by CAT rating and voltage. True-RMS matters on non-linear loads; LoZ helps identify ghost voltage; the fuse and leads must match the category.
- Clamp meter: current without breaking the circuit; confirm the jaw is closed and only one conductor is captured.
- Megohmmeter: insulation resistance on motors and heating elements; a low reading indicates moisture or breakdown, not necessarily a short at operating voltage.
- Manometer: gas pressures in inches of water column; refrigerant gauges read system pressures but are not vacuum instruments.
- Micron gauge: connected at the pump or a dedicated port, not through long manifold hoses; evacuation target commonly 500 microns with a decay test.
- Leak detection: electronic detector, UV dye, or soap solution; each has limits and requires confirmation.
- Torque wrench, flare and swage tools (45° SAE flare), tube cutters, benders, and a nitrogen regulator for purge brazing.
- Scale for charging by weight; recovery machine and certified cylinder.
Materials
- Gaskets, seals, O-rings, and hoses must be compatible with the fluid and temperature.
- Use gas-approved sealant on pipe threads; never use pipe dope on flare faces or on the back of a flare nut.
- Connectors, terminals, and heat-shrink must match wire gauge and current; do not solder where a mechanical connection is specified.
- Brazing filler: silfos for copper-to-copper; stay-brite for lower-temperature joints where allowed.
Worked example
A 240 V, 4500 W element is suspected. Expected current = 4500/240 = 18.75 A and resistance = 240²/4500 = 12.8 Ω at operating temperature. A clamp reading of 13 A with 240 V present points to a partially failed element; a resistance check of about 13 Ω cold is plausible, but 30 Ω or open is not. You verify with the element isolated and the meter zeroed, then compare with the nameplate.
Traps
- Using manifold gauges to judge vacuum.
- Over-torquing flares and splitting the nut.
- Assuming a new instrument is calibrated.
- Using an IR thermometer on shiny metal without correcting emissivity.