HVAC diagrams

Every diagram on the site, free to view and print. Each one links to the guides that use it. Looking for thermostat wiring? See the thermostat wiring diagrams.

Refrigeration & charging

Evacuation rig setup and how to read a vacuum decay test

Refrigeration cycle with superheat and subcooling measurement points

Temperature glide: bubble point and dew point for a refrigerant blend

Where refrigerant leaks usually are on a split system

Gas furnaces

Checking furnace gas pressure: inlet tap, outlet (manifold) tap and regulator

Gas furnace sequence of operation and what fails at each step

Standing pilot and thermocouple: how the pilot safety works and where to test

Where a gas furnace's safety switches and ignition parts are

Where to measure furnace temperature rise

Electrical & controls

Compressor winding resistance test: common, start and run

How to read an HVAC ladder wiring diagram: a condensing unit example

How to tell PSC, constant-torque ECM and variable-speed ECM blower motors apart

Motor rotation: lead end (LE) vs. shaft end (SE)

Run capacitor wiring: one dual capacitor vs. two single capacitors

The 24-volt control circuit: transformer, fuse, thermostat, and the loads it switches

Typical single-phase condensing unit wiring: contactor, dual run capacitor, compressor and fan

Airflow & condensate

Condensate drain on a draw-through coil: pan, trap, vent, slope and float switch

Where to measure total external static pressure

Why an oversized AC leaves a house humid: short cycles vs long cycles

Heat pumps & mini-splits

Ductless mini-split layout: line set, flare joints, interconnect cable and sensors

Heat pump defrost sequence: what each part does before, during and after defrost

Heat pump reversing valve: refrigerant flow in cooling and heating