Air Conditioner Problems on 1994 Dodge Ram Van B250

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I have a A/C problem. My compressor is running and the hi side line is frosting over to the splitter where it goes back to the rear AC coils, the line that goes to the front coils does not get cold past the splitter I spoke of before.The rear coils are getting cold and cooling. This is in a conversion van and the only controls are in the dashboard, the rear fan switch is in the dash as well. I hope somebody can give me some ideas as to where to look or start.
(1) Answer
I sounds like you may have a defective expansion valve at the front HVAC housing. A valve that does not open or is plugged will not allow refrigerant to flow through the evaporator, thus, no cooling.