For 1989-93 models an H-type expansion valve is used to meter refrigerant onto the evaporator in accordance with cooling requirements. A low-pressure cut-off switch is mounted on the expansion valve assembly. The cut-off switch is wired in series with the compressor clutch. The switch cuts off the power supply to the clutch when refrigerant pressure drops off below a given point.
REMOVAL & INSTALLATION
See Figure 1
- Discharge the refrigerant system. Refer to Routine Maintenance for the proper safe procedure.
- Disconnect the negative battery cable. Disconnect the wires from the low pressure cut-off switch.
- Remove the center refrigerant line assembly mounting plate screw. Carefully pull the mount and lines toward the front of the truck, away from the H-valve.
- Remove the valve mounting screws, while holding the valve so that it will not fall. Remove the valve.
- Clean the mounting surface on the line mounting assembly and evaporator.
- Install new mounting gaskets, at the evaporator and line mount.
- Remove the sealing cap from the evaporator side of the new expansion valve. Install the H-valve to the evaporator. Tighten the mounting screws to 30 inch lbs. (11 Nm).
- Remove the sealing cap from the line side of the H-valve. Mount the line assembly to the H-valve. Tighten the screws to 200 inch lbs. (23 Nm).
- Connect the low pressure cut-off switch and the negative battery cable. Evacuate, charge and leak test the system.