Electrical Components
Capacitors, contactors, fuses, motors and boards.
How to Test a Blower Motor: PSC, Constant-Torque ECM and Variable-Speed ECM
How to tell which kind of blower motor you have and test it the right way, from capacitor and amp checks on PSC motors to control signals on constant-torque and variable-speed ECMs.
How to Test an HVAC Transformer: 24-Volt Checks, VA Rating and Shorts
How to test the 24-volt control transformer in a furnace or air handler, how to size a replacement by VA, and how to find the short that killed the last one.
Replacing a Run Capacitor or Contactor: How to Pick the Right Part
How to choose a replacement run capacitor (µF, voltage, dual vs. single, size) and contactor (coil voltage, poles, amp rating), with the common mistakes that bring callbacks.
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.
AC Breaker Keeps Tripping: How to Find Out Why
How to diagnose an air conditioner or heat pump that keeps tripping its breaker: a grounded compressor, a locked rotor, a shorted fan motor, wiring faults, high head pressure or a weak breaker.
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.
Furnace Control Board Fuse Blown (3A): Finding the 24V Short
Why a furnace control's low-voltage fuse blows and how to find the short in thermostat, outdoor unit or accessory wiring before replacing it.
Working Safely on Mini-Split Inverter Boards
Why mini-split inverter boards stay dangerous after power-off, how to verify the DC bus is discharged, and how to approach IPM, voltage and compressor drive error codes.