is it nessecary to remove the dashboard to replace evaporator and expansion valve

I don't believe you need to remove the dash to replace the expansion valve. I don't have particular info regarding the expansion valve but the entire heater-A/C unit appears to come out easy enough and I'd think the valve is in there. I'd have to see the car to be sure about where the valve is but I'm pretty sure you don't have to remove the dash. Sounds like the previous compressor let loose some metal debris into the system and it contaminated the expansion valve. It's probably a good idea to replace the accumulator and flush the system to avoid future problems. If you want to find a specialist, here's our directory link for you: https://repairpal.com/toyota-repair-in-valrico-florida