for the 737-200, the hydraulic is different in the sense that (comparing to -300 to -900)
1. System "A" is purely powered by EDP (engines)
2. System "B" is purely powered by EMDP
All pumps are on during normal operation.
Therefore, on the ground with only electrical power available, you can only pressurize system "B" with either 1 or both EMDP. If you on both EMDP, everything runs faster due to the greater flow.
System "A" is pressurized when you motor or run the engines
OR
There is something called an interconnect switch but only used on ground, mainly for maintenance purpose, which enables system "A" to be pressurized by system "B" EMDP.
But this is off track from the original topic...