AC ventilation question
I very recently replaced the evaporator core/expansion valve along with installing a new receiver/dryer in my 1990 325i sedan. The system has already been converted to R134a. It has no leaks and actually cools effectively most of the time considering the hot summers here in Houston. However, there is an intermittent problem with cold air actually circulating across the evaporator core. Symptoms include only "cool-ish" air coming out of the vents, and ice forming on the metal low pressure return hose. 
What could possibly be causing this? Perhaps something is effecting the proper opening and closing of the flaps that direct cabin air across either the heater core or the evaporator coil; or perhaps there's a valve from the heater line that isn't closing, resulting in hot air being mixed with the cold air???
Thanks for any help!
What could possibly be causing this? Perhaps something is effecting the proper opening and closing of the flaps that direct cabin air across either the heater core or the evaporator coil; or perhaps there's a valve from the heater line that isn't closing, resulting in hot air being mixed with the cold air???
Thanks for any help!