Well the most common issue would be a low refrigerant in the system. Though If the rattling noise was related to the A/C it could be a compressor issue.
The reason why it is probably cold when your driving is because the condenser is being cooled by the air passing over it.
Without spending to much money you could check and try to add some refrigerant to the system. This can be purchased from most auto parts stores in small quantities and will have directions on how to put it in the system and measure how much.
checking and adding refrigerant is about the only thing you can do without taking it to a repair facility to have it hooked up to an A/C machine.
Hope this helps
Accepts greatly appreciated
i'm wondering if the noise was the compressor clutch. now, when i turn on the ac it doesn't make any noise, rather just blows hot. is there a way to check if the compressor is engaging without the refrigerant? can i feel it working if I touch it while its on, etc?
When the A/c is turned on. All you need to do is look at the side of the compressor, you can visually see if the clutch is engaging.
Though if you are to low or out of refrigerant the clutch will never engage because the pressure switch is telling the clutch that there is not enough refrigerant in the system.
When looking at the side of the compressor in the picture the clutch is #2 in the picture.
yes there is a charge valve, the low side pressure port. Somewhere on your A/C lines you will see 2 fittings. They will have a plastic cap on them usually(blue and red usually). You use 1 of these to charge the system. The freon charge should have step by step directions on it to help you.
1 can should be plenty to at least see if this is the issue and enough to kick the compressor on.
Picture to help show where low side charge port should be.
Accepts and feedback greatly appreciated