ok the motor is running fine then or does it has a slight rough idle ?
can you tell me the last time the tune up has been done and the valves adjusted?
ok this noise only happens when the a/c is used or all the time ?
what this a honda a/c or done at a out side shop with after market parts.
ok then i the best advice i can offer you today is to try and isolate the noise and it maybe a a/c clutch or the compressor is failing. and since this is causing the engine to strain its a very strong indication of a a/c failure. in the a/s compressor assy.
can you see if the a/c belt is tight and not loose ? that might lead to the load noise heard,if the belt is tight then you need to return the car back to the shop so they can correct the problem.