Aircondition will not run and the digital thermostat is blank. Unit was running all day.

aircondition will not run and the digital thermostat is blank. unit was running all day.

Check battery and 24 volt transformer .

A blank thermostat indicates a loss of low voltage which originates in your indoor unit. The simplest of reasons would be a blown low voltage fuse or a tripped low voltage circuit breaker.
It could also be that a safety device has tripped, like a float switch... check to see that your unit is draining properly. Is your unit in the attic? Check for a float switch in the pan under it. Is it in the basement? Check for a condensate pump with a float in it.
Also check for a float switch on the condensate drain where it exits the indoor unit.
If any of these are tripped, it could indicate that the drain is clogged.