The main causes of the conditioner condenser not draining is may be Incorrect thermostat setting, no power to unit, airflow problem, duct system unbalancing, circuit breakers, need of refrigerant etc.
It sound as if you've got a clog. Usually you should pour some bleach once a month into the pipe to keep it clear. I recommend getting a technician out to give your a/c unit a thorough maintenance check.
