Electrical & Controls
Capacitors, contactors, motors, thermostat wiring, boards.
AC Compressor Not Starting: Humming, Clicking or Nothing at All
Diagnose a compressor that won't start by what it does: humming points to capacitor or locked rotor, clicking to overload, silence to the control circuit.
Condenser Fan Not Spinning: Capacitor, Motor or Control?
Find out why an outdoor condenser fan won't run, from the fan capacitor and seized bearings to the contactor, wiring and heat pump defrost.
How to Test an AC Contactor: Coil, Contacts and Voltage Drop
Test a condenser contactor the right way, from 24 V at the coil and coil resistance to pitted contacts and voltage drop under load.
How to Test a Run Capacitor: Meter Method and Under-Load Method
Test HVAC run capacitors two ways, with the meter's capacitance setting and under load with amps × 2652 ÷ volts, and know when to replace one.
Thermostat Wiring: Terminal Letters and Wire Colors Explained
What each thermostat terminal does (R, Rc, Rh, C, W, W2, Y, Y2, G, O/B, E, AUX), the usual wire colors, and how to verify a hookup.