frick ice maker

Hi guys
Im re-commisioning an old frick shell ice maker.The hot gas powered piston valves staying shut after harvest,no NH3 in tubes 2nd make,no cam timer installed time relay,s.
1:Should liquid return defrost valve re-open after ice drops and re-starter bar starts ice making to equalize
pressure in order to drop pistons.I can manually re-open piston valves by removing all hot gas from ice maker releaving pilot line.
2:Hot gas may have bought dirt if so clean valves.
3:If piston valves worn are there tolerances available for machining or replacemants.