Exhaust fan

Was helping a friend build his system today, and for some reason my PSU came across my mind and the fact the exhaust fan doesn't blow on it. The PSU is an Antec TP2 500watt, the intake fan on it works as I can see it spinning, but the rear fan on the PSU I have never seen spin. I was wondering is this normal (As I have no powersupply experience) or is it perhaps faulty? Im not saying it doesn't spin, Im just saying iv never seen it spin . I can stick my hand to the rear exhaust of the PSU and feel warm air coming out, but I think this is due to the intake fan on it. So any help would be grateful.

Thanks in advance
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Lemings

Yes, it's normal. It only turns on if the internal temperature reaches a certain level.

You have an Antec SmartPower 500w, not TruePower, btw

Well thats new to me I just done away with the hassle of choosing a PSU by getting one pre-installed with the tx1050b. Thanks for clearing that up, I was getting worried there for a second . On a side note, is there any way I could lower to temp at which it kicks in? (Other than the bios). Again, thanks alot.

no, it's internally controlled. You'd need to do something to the thermistor/sensor inside the PSU.