Ok, so this machine is not being told to turn on. You should be wondering, where is the 24 volt signal?
Now find where the small low volt thermostat wires are coming into the air conditioner and find the 2 little wire nuts.
Remove those wire nuts and test for 24 volts right there.
If, there is no 24 volts right there. Then the problem starts inside at the indoor furnace. So, grab tools and head indoors to the furnace. The furnace is either in your garage or in the attic.
Yes, there is 24 Volts coming in to ac unit.
You know the unit has 24 volts coming in but it does not make it to the contactor coil. The only thing in between the 24 volt input and the contactor on a straight cool system is a pressure switch.
(Note: You should be thinking,” Is the pressure switch bad?” or “Is the suction pressure low, causing the pressure switch to open.”)
Let’s go find out why the pressure switch is open.
Hook your digital refrigerant gauges up to the system now.
Now jumper the two wires leading to the pressure switch, so the system will turn on.
Read your suction pressure if its below 40 psi or 20 degrees then you just might have a refrigeration problem and your pressure switch is simply doing its job and opening to protect the compressor so move to page 18 now to analyze your pressures.
My suction pressure is over 40 psi or over 20 degrees then your pressure switch should not have opened. So it may be bad after all, move to page 13 now where you’ll learn how to change a pressure switch on any AC system.