Alpha-1,2-specific exomannosidase involved in endoplasmic reticulum-associated degradation (ERAD). Delivers misfolded glycoproteins to proteasomes. Forms a complex with PDI1 to process unfolded protein-bound Man8GlcNAc2 oligosaccharides to Man7GlcNAc2, promoting degradation in unfolded protein response. Hydrolysis of terminal, non-reducing alpha-D-mannose residues in alpha-D-mannosides. Protein modification; protein glycosylation. Interacts with PDI1. Present with 656 molecules/cell in log phase SD medium. Belongs to the glycosyl hydrolase 47 family.