As you've noted there are two hoses that attach to the evaporator. One connects directly. The other, which runs all the way from the drier/condensor at the rear of the car, connects to the expansion valve which is connected to the evaporator. It sounds like your car is missing the expansion valve. Any of the vendors have them but you should also replace the drier prior to charging the system - assuming there are no other obvious AC problems.
Dave Bell
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