There are a few instances when the clutch will engage and disengage. 1. if you are low on refrigerant. 2. To keep it from freezing up. 3. When the engine is at WOT it will shut down the compressor. That said you could have a leak, although I am surprised the service center did not detect it when they serviced your car. If you know it is warm enough outside and the system should be running continuously, I would have it checked for leaks. This test is not conclusive by any means, but you can turn the AC on max, turn up the fan to high and keep the windows down to insure a steady supply of warm air to the evaporator. If it is still cycling it is probably low on refrigerant As for the hissing, it is normal to a degree, but I have never really noticed it in the Accord.