problem with hvac

[rfmohlma]

1991 has a problem with the HVAC system. When A/C is set it will begin by blowing cold air then switch to hot. If set on anything other than auto, it will run for a time and then switch itself to auto, where it may blow hot or cold. At dealer repair shop these items have been replaced--actuator motor, f-prog rem, and 2 different sensors. Anyone have any advice?
Thanks

[fatherlarry]

A/C CYCLING PRESSURE SWITCH
Used with fixed orifice systems, this switch is used in place of a thermostatic cycling switch to prevent evaporator icing. It is often located in the accumulator/drier, although it may be located anywhere in the low-pressure side of the system. The switch compares low-side pressure to atmospheric pressure, and may be used, not only to prevent evaporator icing, but also as a low-pressure cut-off in the event that the system loses its refrigerant. This prevents damage to the compressor that results by running it without lubrication.



A/C PRESSURE CUT-OFF SWITCH

A pressure-limiting device that keeps refrigerant pressures below a point where they would blow the pressure relief valve by turning off the compressor, turning on the condenser fan, or both.

Hope this helps