engine/air cond problem ???? HELP

I'm looking to buy a 95 Toyota Supra and my father pointed one thing out, (keep in mind he's always looking for things wrong) and he said that when he turns the air conditioner on (low) the car revs to 1.3ish and stays there for about 10 seconds till it goes super low to 0.5 and then finally after a minute, maintains itself at 0.8 (typical idle rpm). Can anyone help me find the problem so that I can report it and hopefully it could be fixed without a problem. Thanks in advance.

The car is supposed to do that. It has to compensate for the voltage it needs to run the A/C, so it changes idle for a while, no problem.