You made a COMMON error in your first part of your post. You stated you checked the Voltage and spot ON at 120. I could run a 500 foot extension cord and with no load I would have 120 volts. VOLTS is NOT AMPS available. Storage yards rarely have anything above 15 amps and that is usually nominal. Now, you stated your Genset would not start the compressor, so yes, old AC and LOW voltage may have hurt the compressor. IF the AC is over 10 years old and you are doing a makeover, I would just replace the Upper AC unit. Doug