For some HI’S it is helpful to understand how something operates some don’t care as long as they can operate from the Stat and it comes on that is all they desire to know and that is just fine with me but for those that desire to understand more read on.
For the other type of HI go past go don’t collect the $200.00 and go straight to the not for everyone thread.
The posted pic has some arrows that I will refer to by color. The green arrow is from the line side or 240 volt side of the contactor and is how the compressor stays warm when in the off cycle. Power is applied to the compressor thru this bar when no crank case heater is in use on a A/C unit. The red arrow is the other side of the line voltage 240 volts. For your info if one was to press down with a insulated screw driver on the points where the red arrow is indicating the A/C unit would operate the compressor and the outdoor fan would turn on the indoor fan would not activate.
The yellow arrow indicates the wire from the neutral side or common side of the step down 24 volt transformer.
The blue arrow indicates the hot side of the step down transformer which travels from the transformer thru the thermostat and in series with any safety devices on the unit such as low or high pressure switches. When the thermostat calls for cooling and all of the safety switches are in the normally closed position, 24 volts is applied to the holding coil on the contactor and the unit starts.
Keep in mind when the disconnect is in the on position for the A/C unit with this type of contactor the compressor has 120 volts applied at all times. This type of contactor is referred to as a single pole contactor. Double pole contactors are also found on A/C unit and of course the double pole breaks both sides of the 240 volt power source thus the compressor has no voltage applied during the off cycle