Rooftop AC 3D wiring model

Coleman-Mach 120 V, cool mode

An AC is a chain of switches to the compressor, with the fan running off the selector switch. Capacitors help the motors start.

Parts in this model

Breaker: If it trips, voltage stops here. Find out why before you reset it.
Selector switch: The mode switch. Cool positions connect the line to the fan and to the compressor path.
Compressor relay: Closes when the thermostat calls for cooling. On the P.C. board it is COM and N.O.
Freeze switch: Opens if the coil gets too cold, which kills the compressor and leaves the fan running. Low airflow and a dirty filter are the usual reasons.
Overload: Inside the compressor, in series with the common terminal. It opens on high current or high temperature.
Fan motor
Fan capacitor: On the fan motor's brown wires. An open fan capacitor leaves the fan unable to start properly.
Start cap + ptcr: Helps the compressor start. Wired in parallel with the run capacitor.
Run capacitor: Gives the compressor starting torque and keeps it running. An ohm meter can only tell good, open, shorted or grounded. You need a capacitor tester to check the µF.

Off. The selector is off, so nothing is running.
Selector on COOL: fan runs. Power goes through the breaker and the selector to the fan. The fan capacitor helps the fan motor start and run.
Thermostat calls: compressor starts. The compressor relay closes. Power now flows through the freeze switch and the compressor's own overload. The start capacitor and PTCR help it start, and the run capacitor keeps it going.
Cooling. Fan and compressor run together. If the coil ices up, the freeze switch opens and the compressor stops while the fan keeps running.
Thermostat satisfied. The compressor relay opens. The fan keeps running until you switch it off.