cooling fans.

[bigyagi]

i have always thought that my fans are noisy, and recently, after completing some electrical work, i was checking the fuses and relays, and i gave each relay a good push, to make sure that they were seated ok.
anyhoo, driving along, i hear the familiar click, and suddenly, only one fan now on, whereas before, i always had the two running but my oh my, how quiet it is! another click, and its off. when i got home though, the one fan was running even after i turned off the engine. i reached under the dash, and gave the relay a prod, and the fan turned off. hmm. question? can anyone give me the proper explanation, of how the fan{s} are supposed to work? since i bought the car, the two fans have always switched on together, and off. when the engine is turned off, one fan runs at low speed for a minute, or so, then turns off, and that part is ok.
so, should it be one fan, or two?
bob.

[nynor]

one fan should run at low speed when car is turned off and hot. with AC on, both should run at high speed, when engine is hot, both should run at high speed. sounds like the relay may be crapping out. have similar problems with my fans.