Hello el_steak,
I am in the middle of installing my Aqualogic PS4.
The main difference is in the number of outputs
P4 - 4 relays, 3 valves outputs, 1 heater control, 3 temperature inputs
PS4 - 4 relays, 4 valve outputs, 2 heater controls, 3 temperature inputs
http://www.poolwarehouse.com/Aqua-Logic ... trols.html
The PS4 unit uses the same internal relay for both Valve 4 and Heater 2 - you can't use both at the same time. I am not familiar with the P4 main circuit board, but at least on the PS4 main circuit board, if you don't need a Valve 4/heater 2, there is a fairly inexpensive way to use this 28 Volt AC output to control a fifth relay.
Also, the local display and remote displays are different between the P4 and PS4
P4 -
http://www.haywardnet.com/products/Manu ... ual196.pdf
PS4 -
http://www.haywardnet.com/products/Manu ... ual200.pdf
Either the P4 or the PS4 is able to deal with Pool Only, Spa Only, or Pool/Spa combinations. However, P4 can only handle Pool/Spa combinations where the Pool/Spa equipment (filter pump, etc) is shared. The PS4 is a little more advanced where it can handle Pool/Spa combinations where there is separate (dual) equipment for both the pool and spa.
Also, it appears that the PS4 can do "Group" functions, which seems to be AquaLogic's term for a macro function. The P4 doesn't appear to have a "Group" function.
Remember that a base P4 (or PS4) still needs valve actuators (GoldLine GVA-24 or equivalent Jandy or Pentair). Also, the base units do not come with remote displays and/or floating (and waterproof!!) wireless spa remotes.
The best prices I have found (except for my lucky Leslie's Pool purchase) is $629 for a PS4, $79 for GVA-24 valve actuators, $165 for wireless spaside remote, and $269 for wireless table top remote at
www.aquapoolstore.com. The best price is $115 for the wireless base unit is at
www.h20poolproducts.com, alothough the first store is not far behind for this piece at $119. CAVEAT: I have never done business with either store, and I didn't have the time to compare shipping charges in this price search/comparison.
I hope this helps.
Titanium