How to Check step by step Refrigerant Circuit Problems part 6

Refrigerant Circuit Problems

System Condition 10
1. Low pressure gauge reading is too low.

2. High pressure gauge reading is too low.

Note: Ambient temperature is above 21°C (70°F).

3. The temperature of the air flow from the evaporator is partially cool or warm.

4. 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

Note: The inlet to the expansion valve will be warm during normal operation.

1. If the expansion valve inlet is cool to the touch, perform the following procedure:

* Position the air conditioner temperature control knob to the maximum COOL position and 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. In order 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 the Service Manual, SENR5664, "Refrigerant Recovery" section in Testing and Adjusting.

* Replace the expansion valve. Refer to the Service Manual, SENR5664, "Expansion Valve - (Air Conditioner) Remove and Install" section in Disassembly and Assembly.

Note: The sensing bulb must be installed correctly in order 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 in order 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 the Service Manual, SENR5664, "Refrigerant System - Evacuate" section in Testing and Adjusting.

* Charge the system with the correct amount of refrigerant. Measure the refrigerant by weight. Refer to the Service Manual, SENR5664, "Refrigerant System - Charge" section in Testing and Adjusting.

* After the system is charged and operated for a minimum of ten minutes, perform a performance check. Refer to "Performance Checks for the Air Conditioning System" section.

2. 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 outlet pipe. The insulation must be around the sensing bulb and the clip on the evaporator outlet pipe.

* In order to ensure the correct systems operation, perform a performance check.

3. Replace the in-line dryer or replace the orifice tube.

* Evacuate the system. Refer to the Service Manual, SENR5664, "Refrigerant System - Evacuate" section in Testing and Adjusting.

* Charge the system with the correct amount of refrigerant. Measure the refrigerant by weight. Refer to the Service Manual, SENR5664, "Refrigerant System - Charge" section in Testing and Adjusting.

* After the system is charged and operated for a minimum of ten minutes, perform a performance check. Refer to "Performance Checks for the Air Conditioning System" section.


Illustration can look at above

Expansion valve in the closed position (Typical Example)

(1) Capillary tube

(2) Expansion valve diaphragm chamber

(3) Inlet

(4) Outlet

Note: For expansion valve systems, refer to Step 1. For orifice tube systems, refer to Step 3.