You have a small transformer on the roadside of the AC after you take the shroud off. This transformer steps 125 volts (my current measurement) down to 24 volts and sends the current down to the thermostat on the wall. The compressor is intended to operate on 115 volts, 60 cycle current and if voltage is under 103 volts, the compressor may not start. Make sure the themostat is set below room temp. Turn the rotary switch of the AC on. The comp. relay should be energized. If not, short between Y and R terminals (noted on your wall thermostat after removing the cover) with a short piece of jumper wire. This is a low voltage circuit. If the comp. relay closes, thermostat is defective or circuit to transformer is faulty. I found no current at my thermostat and less than 9 volts of current on the stepdown side of my transformer. I went to an electrical supply house (taking the old transformer with me) and found one to match which was only slightly larger in exterior dimensions than the original. I made a new mounting bracket, wired it in and the compressor fired up as soon as I turned the AC on. Be careful if you are not connected to a 30 amp circuit. An extension cord to a 15 amp circuit and dogleg adapter to 30 amp male plug can be used to check the unit but should not be run for more time than to see if the fan is running and the compressor kicks on. You may be lucky and find it is only the transformer. Also check that all wires are tight at the thermostat. Let us know what you find.
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