Core: Safety, Tools, and Refrigeration/Electrical Fundamentals
Safety, tools, and the fundamentals behind every question
Start with the hazards: lockout/tagout before opening any disconnect, PPE (goggles, gloves, insulated tools), and refrigerant handling under EPA Section 608. Refrigerant vapor is heavier than air and displaces oxygen in pits and basements; liquid refrigerant causes frostbite; never pressurize a system with oxygen or compressed air. Treat a capacitor as live until you have proven it discharged.
Tools to recognize: manifold gauge set (compound low-side gauge, high-side gauge), micron gauge, vacuum pump, clamp meter, multimeter, manometer, and digital thermometers. Common traps include reading a capacitor without discharging it, leaving the manifold center port open during a leak check, measuring vacuum at the pump instead of at the system, and mixing wet-bulb with dry-bulb readings.
Refrigeration basics: the four components (compressor, condenser, metering device, evaporator), the pressure-temperature chart for each refrigerant, superheat at the evaporator outlet, subcooling at the condenser outlet, and the state of the refrigerant through each part of the cycle. Electrical basics: Ohm's law (E = I x R), series versus parallel circuits, 24-volt control circuits, contactors, start and run capacitors, and telling a load from a switch on a wiring diagram.
Worked example: a 24-volt contactor coil measures 24 ohms across its terminals. I = E/R = 24/24 = 1 amp. If that same coil draws 2 amps, its resistance has roughly halved, so the coil is shorted and the control-circuit fuse or transformer is at risk.