Are you running the fan speed on low??? This (on SOME units) has caused the insides/guts of the A/C to freeze up.
Freezes up, melts, rains inside.
Older units, with A/C installed on the slope of the roof, had trouble with certain low profile A/C units.
We did, we thought one of the yorks did not make it outside, we found a puddle pretty much under the A/C unit. Al was beginning the mopping up procedure when the A/C unit peed all over his back.
He sure yelped, guess the water was a bit cold??
Checking the drain as suggested is also a good idea.