System Condition 4
1. Low pressure gauge reading is below normal. For normal operating pressures, refer to Table 1.
2. High pressure gauge reading is normal to the below normal range. For normal operating pressures, refer to Table 1.
Note: Ambient temperature is above 21°C (70°F).
3. The temperature of the air flow from the evaporator is partially cool.
4. The high side liquid line or the receiver-dryer is frosted. The high side liquid line or the receiver-dryer is cool to the touch.
Probable Cause
Restriction in the high pressure liquid line can cause the refrigerant to be removed from the evaporator at a faster rate. The restriction can cause the evaporator to be low on refrigerant from the receiver-dryer or from the in-line dryer. Clogged filters or a failure of the blower motor can cause possible restrictions to the air flow.
* Recover the refrigerant. Refer to the Service Manual, SENR5664, "Refrigerant Recovery" section.
* If the restriction is found at the receiver-dryer, replace the receiver-dryer. Refer to the Service Manual, SENR5664, "Receiver-Dryer - Remove and Install" section in Disassembly and Assembly.
* If the restriction is found at the in-line dryer, replace the in-line dryer.
* If the restriction is found at the liquid line, replace the liquid line.
* Cap all the open lines and fittings.
Note: Restrictions of the refrigerant flow are identified by frost or cold spots in the line. Also, restrictions of the refrigerant flow are identified by frost or cold spots in the receiver-dryer or the in-line dryer.
* Replace filters or remove any of the restrictions.
* 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.
System Condition 5
Note: The system only cools the cab in the morning and in the evening. The system does not cool the cab during the hot part of the day.
1. Low pressure gauge reading is normal, but the gauge reading may drop into the vacuum range during the testing procedure. For normal operating pressures, refer to Table 1.
2. The high pressure gauge reading is normal, but the gauge reading is below normal when the low pressure gauge drops into the vacuum range. For normal operating pressures, refer to Table 1.
Note: Ambient temperature is above 21°C (70°F).
3. Air flow from the evaporator is very cold, but the air flow will become warm when the low pressure gauge drops into vacuum.
Probable Cause
The system has a large amount of moisture. The desiccant in the receiver-dryer or the in-line dryer is full of water. The water is released during high ambient temperatures. Ice collects in the orifice or the expansion valve and the ice can block the flow of refrigerant.
* Recover the refrigerant from the system. Refer to the Service Manual, SENR5664, "Refrigerant Recovery" section in Testing and Adjusting.
* Replace the receiver-dryer or the in-line dryer. Refer to the Service Manual, SENR5664, "Receiver-Dryer - Remove and Install" section in Disassembly and Assembly. For in-line dryers, refer to the Service Manual, SENR5664, "In-Line Refrigerant Dryer - Remove and Install" section in Disassembly and Assembly.
* Remove the moisture from 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.
Note: Low pressure (suction) drops into vacuum when ice forms in the expansion valve. High pressure (discharge) drops when low pressure drops into vacuum.
