An evaporator problem doesn't come and go. The problem they have is that they leak.
Find an independent that will do a florescent leak test. Have them find out if the system is low and then refill it and see how long it lasts and then find the leak for sure with a black light.
There are plenty of electrical reasons for the system to not function and then function. Not so with a leak.
Bosch Master, ASE Master, L1
33 years MB technician