How do I diagnose my AC leak?

[MTL_4runner]

What would you recommend if I have a clicking sound coming from under my hood when the a/c is on?

The AC (or defroster) will cycle in use (except when AC is on full) and everytime it comes on or off you will hear a click coming from the engine bay. This should happen around once every few minutes. If you hear constant or rapid clicking it may be a sign you are low on refrigerant or you have a problem with the AC clutch (or electrical circuit). My first suggestion is to get your system serviced (evac and refilled) and see if that helps.

[4x4mike]

What would you recommend if I have a clicking sound coming from under my hood when the a/c is on?

If it's clicking on and off pretty frequently (maybe once every 1-2 minutes)the system is probably low and it's building pressure with a low system when requires more compressing. It could also be a malfunctioning pressure switch. If the PS is bad the system will protect itself by cutting current to the clutch hence the constant on and off.

[20005spd]

I'm no car expert but I know this is not normal. I have never heard it click before but my heater has started sucking lately and I'm expecting the a/c will suck too this summer. Is there any do it yourself checks I could do before I take it somewhere?

open the hood, run the a/c system full cold. watch your a/c compressor clutch to see if and how often the clutch cycles on and off. you can also buy a cheap set of a/c gauges to see what the psi is at. with the car off and hi and lo psi equalized you should have around the same psi reading in both hi and lo as the outside temp in Fahrenheit.

but you could save all your money and time and bring it somewhere and have them do all that work

edit: your heat also has nothing really to do with your a/c