I need help please. I know nothing about cars.
 

Hello Everyone,
This is my first time using this forum with the hope that I will get the right diagnosis. I drive a Camry 2007 LE, 4 cylinders(133k miles), and in the past three weeks my AC suddenly stopped blowing cold air, only hot air. I have a friend who checked my Freon level looking for any gas leakage, but it wasn't the case. While driving recently, a very annoying grinding noise is coming out of the hood. I checked the source and asked a mechanic and he said that my AC compressor needs to be replaced. The noise is coming off the compressor and the belt area.However, I am not convinced that the compressor itself should be replaced. The annoying grinding noise that I am talking about happens when my AC is off. Well, of course the noise gets louder when I turn the AC on, but isn't this the case in any normal functioning car. The grinding sound starts as soon as I start my engine, even when the ac is turned off. Do you guys think that the compressor needs to be replaced or are there any other tests that I can run to detect if its the compressor that's malfunctioning. I am sorry if my assumption is wrong. I am a medical student and I know nothing about cars, so I hope I can get some help from you guys.I jumped into this forum because I don't want to replace my compressor before being sure that it is the source of the problem. BTW, I live in Texas and it is extremely hot at this time, in case it is relevant.
Thank you in advance,
David.

Have your radiator fans checked too.

I think that your compressor is shot by the sounds of it.
Your car (the same as mine) has a single serpentine belt that all of the accessories are run off of, like A/C compressor, alternator.
Even when your A/C is not turned on, this single belt is cycling along in accordance with engine speed. When your A/C is off, the compressor's clutch is not engaged, thus allowing the pulley to spin freely but not actually turn the compressor. Just the pulley where the belt rides spins.
When you turn on the A/C, the clutch engages and now the compressor is actually functioning and circulating the refrigerant through the HVAC system.
Your situation sounds like the clutch and/or bearings are bad in the unit. You should get this fixed because if the bearings seize, the pulley will stop turning. The belt will continue to be dragged over it and the belt will get destroyed very quickly.

Also had to replace my car's compressor and it was expensive.