Hi, I have a 2002 Mustang GT. Whenever I turn on the A/C and I drive there is a hissing noise coming from the hood. The noise stays for around 5 seconds or so, then it turns off. The noise comes off and on too. Is my A/C compressor going bad? Low on freon? What could it be?

 

You need to replace the A/C compressor, The clutch is worn out

 

Before you jump to the compressor, which could just be cycling on and off due to low refrigerant, I would take it to an AC mechanic for a check up. You might also have a leak which they can check for and fix for a lot less money than the cost of the compressor.
This is what you can do yourself:
1. Turn your car on with the windows down and turn your ac on max and fans on high.
2. Open your hood and and see if the clutch on the compressor is engaging. To tell this there are three round things on the pulley of your AC compressor. When the clutch is engaged these will spin. They should contiuously spin if serviced correctly. If they cycle on and off it's probably because of low refrigerant.
3. If you have a set of AC Guages or can borrow some. Look at what pressure your high and low side are. The high should be anywhere from 180-320 PSI while the low should stay between 30 and 40 PSI. This is while running. When the engine is off the pressures should equalize on both sides but are usually at least 70 PSI but it varies depending on outside temperature.
4. Find out where it's hissing from. If it's refrigerant leaking it may be visible to see, depending on the size and locaton of the leak.

Anyways it's always good to be informed when you talk to someone about your AC problem so you can save troubleshooting time and time costs money.

 

where is high and low sides located at? i found one towards the back of the engine? is this the high or the low? and where is the other one