In the end, there must be a decent amount of heat generated by the mechanical A pumps because there is a heat exchanger in one of the fuel tanks for cooling . And the book says that you will get an overheat if the associated fuel quantity is too low, yet there is no overheat warning for the A system.
But perhaps this is an unusual enough situation that it didn't warrant overheat lights. Why? If your fuel is that low, your engines(and therefore the mechanically driven A pumps) will be shutting down soon enough anyways unlike the B pumps which could be left on all day with the fuel quantity low, perhaps by maintenance or pilots after landing with not much fuel.
Both A and B pumps appear to have the third port for case drain.
Last edited by JammedStab; 2nd Nov 2012 at 15:13.