There may be circuitry to not let the Compressor on the A/C unit to start under low Voltage or the Compressor will just not start at a low Voltage . The Inverter may even have something to do with it also with protection circuitry for output You could also have defective Batteries & as you pointed out , it may be the Balmar Panel , maybe for some reason it was not up to date on Battery charge % .
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