When I switch the unit to cool,it will come on but shuts down after a few minutes ,then a minute or two later it tries to start but doesn't,then a few seconds later it tries again but doesn't,then on the third try it does come on but doesn't seem as though it cools.the if it does cool down and satisfies as soon as it calls for cool,it goes through that same routine.Sometimes it does not cool at all.

Could be a bad contactor, low Freon or other problems. Have an HVAC tech look at it.