Upon arrival, I found that the outdoor unit was not turning on. I search the diagnostic section of the thermostat and found an odd older code. It had to do with liquid refrigerant returning to the compressor. I inspect the old filter. It was pretty dirty, but it wasn’t awful. Customer stated he changed it today. I inspected the evaporator coil and recommended doing a minor cleaning on it. I power cycled the unit. Once I rebooted, it began to cool normally. I checked the charge and amps to find the system is cooling well.