Thermostat
Thermostat wiring, settings and placement.
AC Short Cycling: Why the Compressor Turns On and Off Too Often
How to diagnose an air conditioner or heat pump that short cycles, using how long it runs and what stops it: thermostat problems, safety switches, low charge, airflow, and oversizing.
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.
Heat Pump Auxiliary Heat vs. Emergency Heat: When Each Runs and Why Aux Runs Too Much
The difference between auxiliary heat and emergency heat on a heat pump, what's normal, and how to diagnose a heat pump that runs on aux heat constantly or never brings it on.
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.
Millivolt Wall Heaters and Floor Furnaces: Thermopile and Gas Valve Troubleshooting
How millivolt (powerpile) systems on wall heaters, floor furnaces and fireplaces work, how to test the thermopile, and how to find the voltage drop that keeps the main burner from lighting.
Thermostat Blank or No Power: Finding the Missing 24 Volts
How to troubleshoot a blank thermostat: batteries, the C wire, the furnace door switch, a blown board fuse, a tripped float switch, the transformer and power to the air handler.
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.
Furnace Short Cycling: 7 Causes and How to Pin Down Which One
Diagnose a gas furnace that lights and shuts off too soon, from flame sensing and limit trips to oversizing and thermostat settings.
Heat Pump Blowing Cold Air in Heat Mode: What's Normal and What's Not
Tell normal heat pump behavior (cool-feeling air, defrost) from real faults like reversing valve, O/B setup, low charge and aux heat problems.
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.