Error Codes & Blinking Lights
Board LEDs and display codes.
Furnace Blowing Cold Air: A Diagnostic Order That Finds It Fast
Why a gas furnace blows cold or lukewarm air, in the order to check it: thermostat fan setting, lockouts, flame proving, limits, gas supply, and duct leaks.
Furnace Inducer Motor: Testing, Noises and When It's Really the Pressure Switch
How a furnace draft inducer works, how to test one that won't start, runs noisy or runs but won't prove, and how to tell an inducer problem from a pressure switch or venting problem.
Heat Pump Defrost: How It Works and How to Troubleshoot It
How heat pump defrost works on time-temperature and demand defrost boards, what's normal during defrost, and how to diagnose a heat pump that ices up or defrosts too often.
Mini-Split Not Cooling or Heating: A Diagnostic Order for Ductless Systems
How to troubleshoot a ductless mini-split that runs but won't cool or heat: error codes, mode and remote settings, filters and blower wheels, the outdoor unit, sensors, communication and charge.
Furnace Blinking Light Codes: How to Read Them on Any Brand
How furnace control boards report faults with LED flashes, how to read the code correctly, and what the common code categories point to.
How to Test a Mini-Split Thermistor (Temperature Sensor)
Test a mini-split room, coil, discharge or outdoor temperature sensor with an ohmmeter and the manufacturer's resistance table, and find out whether the sensor, wiring or board is bad.
Mini-Split Communication Errors: How to Troubleshoot Indoor-to-Outdoor Faults
A step-by-step approach to mini-split communication faults between the indoor and outdoor units, covering wiring, polarity, voltage and boards.