Lexus Repair: AC Humming on Hot Day, vacuum leak, dangerous level

Question
Hello Zak,
My 95 SC400 ,has 150K+ miles, makes humming noise when AC is running. The noise is more odvious when AC is running on a hot day. And when AC is turned off with brakes applied the RPM would drop to dangerous level. And the car did stall prior the air intake manifold got cleanup. And hot air can be felt coming from underneat the car. Once again the problems are more profound on hot day.
Thank you
Sean  

Answer
Hello Sean, Well if the compressor is the original one I would say it has lived a long life. Here in Arizona they only last about 80k miles. As far as the low idle while braking it is hard to say what that may be, possible brake booster causing vacuum leak.