Hi Allen
In theory your two controllers are driving 8+4=12 valves.
There are two considerations that might be conflicting with a replacement of these controllers with a single new controller.
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Valves may be driven by two types of operating voltage. Either AC or DC.
To make sure both controllers use the same operating voltage you can check the power supply on both controllers. It should read 24 V AC (usually) or 24V DC (rarely).
Better yet, use a voltmeter and verify by probing between ‘Common’ and any one of the controller terminals ‘1’…‘12’. -
Create a map of your sprinklers and verify that every controller output is connected to one (and only one) sprinkler. You want to make sure that the current installation has no built-in ‘trick-circuits’ to create some logic like run sprinkler 3 when both controllers are active on it.
If the above points are verified you are free to replace with any controller that can drive your valves (AC or DC).
Cheers, Sebastian