The EPR is designed to keep a minimum pressure of about 30 psig in the evaporator to keep the refrigerant temp above freezing. This means it will shut off the port to the compressor until the pressure in the suction line, from the evaporator, rises to 30 psig. So at atmospheric pressure the EPR would be shut and turning the compressor would pull an vacuum inside the compressor thus result in little flow out the compressor discharge. The only way the “bench test” would be to rig up an old compressor suction fitting and setup a means to add pressure to the fitting. It’s just not to very feasible.
Ron