a/c starts and stops working

If you mean the compressor clutch stopped spinning then I understand. If the system is low on freon the compressor will cycle on and off just as you are experiencing. Buy a can of freon and adaptor hose,locate the LOW side line which is located near the heater core, it should have a BLACK CAP on the valve. NEVER, NEVER touch the RED CAP at that is the high pressure side. Remove the Black Cap and follow the instructions on the freon can. Only use what you need. The compressor should continue to work with the controls set to cool. If it again stops or intermittingly works, you have a leak that must be repaired.

If your vehicle has automatic temperature control (where you set a temperature) the blower will stop when the vehicle reaches the temp you have it set at. It works just like a home furnace or central air unit.