GEAR AS 2418273 - Caterpillar

System Condition 2
Low-pressure gauge reading is below normal. For normal operating pressures, refer to Table 1.
High-pressure gauge reading is below normal. For normal operating pressures, refer to Table 1.Note: Ambient temperature is above 21° C (70° F).
When the air conditioner is operated at maximum cooling, the cooling performance is insufficient.
Moisture (water) or frost is on the expansion valve inlet or orifice tube assembly.Probable Cause
The problems that are described in Step 1 through Step 4 can be caused by the following faults:Note: The following faults will cause a restriction of the flow of refrigerant to the evaporator.
Improper operation of the expansion valve (stuck valve)
Blockage at the evaporator inlet
No charge in temperature sensing bulb
Illustration 2 g00409166
Expansion valve in the Open position (Typical Example)
(1) Capillary tube
(2) Expansion valve diaphragm chamber
(3) Inlet
(4) Outlet
Illustration 3 g00415456
Expansion valve in the Closed position (Typical Example)
(1) Capillary tube
(2) Expansion valve diaphragm chamber
(3) Inlet
(4) OutletNote: The inlet to the expansion valve will be warm during normal operation.
If the expansion valve inlet is cool to the touch, perform the following procedure:
Set the air conditioner temperature control switch to the maximum COOL position and set the fan switch to the HIGH position.
Cool the head of the expansion valve diaphragm chamber and capillary tube with ice or liquid nitrogen. Record the low-pressure gauge reading. The low-pressure gauge should indicate a vacuum.
If a vacuum is indicated on the low-pressure gauge, place a hand over the expansion valve diaphragm chamber. The hand will warm the expansion valve diaphragm chamber. To ensure the correct operation of the expansion valve, cool the head of the expansion valve diaphragm chamber and the capillary tube with ice or liquid nitrogen again. If the operation of expansion valve is correct, refer to Step 2.
If the low-pressure gauge does not indicate proper operation of the expansion valve, remove the refrigerant from the system. Refer to Testing and Adjusting, "Refrigerant Recovery".
Replace the expansion valve. Refer to Service Manual, SENR5664, "Expansion Valve - (Air Conditioner) Remove and Install" section in Disassembly and Assembly.Note: The sensing bulb must be installed correctly to ensure the correct operation of the expansion valve. Clean the location for the sensing bulb with steel wool or emery paper. Use a 8P-6355 Clip to attach the sensing bulb securely to the evaporator coil outlet pipe. Completely cover the assembly with 5P-7070 Strip Insulation.
Evacuate the system. Refer to Testing and Adjusting, "Refrigerant System - Evacuate".
Charge the system with the correct amount of refrigerant. Measure the refrigerant by weight. Refer to Testing and Adjusting, "Refrigerant System - Charge".
After the system is charged and operated for a minimum of 10 minutes, perform a performance check. Refer to Testing and Adjusting, "Air Conditioning Performance - Test".
If the low-pressure gauge indicates the correct operation of the expansion valve, perform the following procedure:
The sensing bulb must be in the correct position on the evaporator outlet pipe and the sensing bulb must be the correct distance away from the evaporator outlet. The bulb should be upstream from the pressure sensing connection in the evaporator