I've been working on older true prep table. The evaporator keeps freezing up. I've replaced the cap tube with same size and length and dryer. Ive brazed in access fittings on high and low it's a R134a system. The thermostat went bad on it also so I replaced it. Then I've replaced the evaporator fan too. At start my cabinet temp was 80 degrees. My ambient 95 degrees. My suction was 17 degrees and head 250. Any help would be appreciated!