Has any circuit breaker tripped?
Look for tripped breakers in the units wherever there is a possibility. Turn the tripped breaker to the “off” position. Now turn the breaker “on”. If the breaker trips again, then call a professional for help. Most of the time tripped breakers are due to a short circuit or a grounded circuit. In some cases you may require to replace the circuit breaker as it has worn out with time after multiple trips.
Is the condensate drain clean?
The condensate drain is located outside the house. It is usually a PVC pipe that has a cross-section of 3 inches. Now take a vacuum cleaner and connect it to the condensate hose and turn it on to suck out any obstruction. In most cases, these drains get clogged due to algae. When you power on the AC condensation forms on the evaporator coils, where the hot air gets cooled. This condensate water needs to be vented out of the house. If the water is unable to move, it starts dripping. Cases of HVAC fires have been reported that were caused due to dripping water. However today you have units with drain float switch that will shut down your AC if the condensate water rises above the danger limit to overflow.