if it is blowing cold for awhile then all of the sudden changing to ambient air than more than possibly a motor is cutting out on the outdoor unit. See if you can tell when it happens next time - go outside and you may catch the condenser fan off and the compressor maybe running (albeit for a short period till it cuts out on internal overload) if so pull disconnect (http://www.thermal-medics.com/my-videos/how-to-use-the-disconnect/)
both will already be off
compressor off and just the condenser fan motor running
the reason they come back to life later is the overload has time to cool and reset and all seems normal again...
if any of the scenarios are happening get it sorted out because it is quickly taking time off the life of the compressor for sure
does it happen during the hottest time of day?