Can someone answer a power supply fan question?

I have been dealing with my system locking up for about a week. My fans were filthy so I cleaned the power supply fan and the other fan inside very carefully. When I started the system back up, the power supply fan is not running. Does this fan only kick on when necessary or is it supposed to be running all the time? I feel air and I'm assuming it's coming from the smaller fan. I don't even remember whether the thing was running all the time before!

Any help would be greatly appreciated! Thank you.

 

Do you have a fan control header hooked up to it? Thats about the only time its off(when thermally controlled), otherwise it shold run at all times.

 

What is your system?
There are some ultra quiet systems where the psu fan is controlled, but in most this fan operates continually.
Are you SURE you meant the power supply fan? How did you clean it? Did you disassemble the psu unit? Most psu fan wires are soldered to their cicuit boards.
Many systems have several fans for the processor, case, graphics hard drives to name but a few.

Studio T