If you have DIP switch 2 off (default) for Solar Heat, and you have a temperature sensor connected to the solar sensor terminals then you should have a Solar Heat function show up that you can enable and disable. When Solar heat is used it is hard coded to VSP speed 7. As Allen said, show us your VSP speed table. What does speed 7 say, it should be named Solar heat unless you have changed it, regardless the pump will go to speed step 7 if, 1- you have a temp sensor across the solar terminals, 2 - you have solar heat enabled, 3 - the pool is calling for heat, 4 - the solar temp sensor is at least 5 degrees above the pool temp, and lastly 5 - if speed step 7 is set to a faster speed then your regular 2000 rpm.
With the aqualink system the fastest active speed always takes presidency. If speed step 7 is set to less than 2000 rpm then nothing will happen when the solar activates as you are already going faster than speed step 7.
Please show us the VSP speed setting screen as Allen displayed so that we can figure out what is going on. For example here is that screen from my system.

Here you can see that speed 7 is setup for Solar Heat (the default name) and it's set to be faster than the default pool speed of 2100 RPM.