Refrigerant Compressor - Test
Identifying compressors that function is the purpose of this instruction. Compressors that function should be identified before the compressors are removed from a machine. Compressors that function should produce both high pressure and low pressure. If the compressor fails any one of Steps 3, 5, 7, or 8, then the compressor is considered to be a "failed" compressor. Please indicate the steps which were failed by the compressor in the Warranty Claim Story.
Note: If the compressor fails one of the steps, then the air conditioning system should be diagnosed in order to find the root cause of the failure. The root cause of the failure should be repaired. If the compressor is considered to be "good", then additional assistance with the diagnosis of the air conditioning system can be found in Service Manual, SENR5664, "Air Conditioning and Heating R134a for all Caterpillar Machines" or by contacting your Caterpillar dealer.
Procedures
1. Check the air filters. If the complaint of the customer is poor cooling of the cab, past experience has shown that plugged air filters can often be the cause. Most air conditioning systems have return air filters and fresh air filters. Be sure to check both the return air filters and fresh air filters.
Air Filters Checked? Yes or No.
2. Test the voltage. While the engine is running and the air conditioning is switched ON, check the voltage at the compressor. The voltage at the compressor should be a minimum of 11.5VDC for a 12VDC system or 23 volts for a 24VDC system. The routinely used electrical loads should be turned ON. For example, a lighting system which is added by the customer could cause available voltage to decrease below the minimum specification.
Voltage Checked? Yes or No.
Measured Voltage Level: ____ (volts)
Note: When the air conditioning is switched ON, for air conditioning systems with a Compressor Protection System (CPS), there is approximately a 30 second delay before a voltage signal is detected at the compressor. Air conditioning systems with CPS can be identified by the use of either the 169-7443 On Delay Timer As or the 212-2204 Air Conditioner Control Gp . In most applications, the electronic control group is located near the compressor.
3. Test the resistance. Measure resistance of the clutch coil at the compressor connector. For 12VDC models, measured resistance should be within -0.3 to +1.1 ohms of the amount which is listed in the Specifications section of Service Manual, SENR5664, "Air Conditioning and Heating R134a for all Caterpillar Machines", "Refrigerant Compressor". For 24VDC models, measured resistance should be within -1.3 to +5.5 ohms of the amount which is listed in Specification section of Service Manual, SENR5664, "Air Conditioning and Heating R134a for all Caterpillar Machines", "Refrigerant Compressor". The resistance ranges which are listed above compensate for the effect of temperature on the clutch coil. The values which are listed in the Specifications section of Service Manual, SENR5664, "Air Conditioning and Heating R134a for all Caterpillar Machines", "Refrigerant Compressor" are nominal for 20 °C (68 °F).
Resistance Checked? Yes or No.
Measured Level of Resistance: ____ (ohms)
4. Check the belt tension. For new belts and old belts, use the 144-0235 Belt Tension Gauge . For a new belt installation, the initial belt tension for a compressor which drives the system without an auto tensioning device should be 534 N (120 lb). For used belts, the belt tension should be 400 N (90 lb).
Belt Tension Checked? Yes or No.
Measured New Belt Tension: ____ (N) or (lbs)
Measured Old Belt Tension: ____ (N) or (lbs)
Note: The electrical power supply to the compressor should be switched OFF in order to perform this test.
# Test the rotation. Rotate the compressor in the direction of belt travel by turning the nut on the end of the main shaft of the compressor. Rotation should be smooth with no binding.
Rotation Checked? Yes or No.
Rotation Smooth? Yes or No.
1. Check the charge level. The air conditioning system must be correctly charged per Caterpillar specification or an incorrect diagnosis will occur. Recovering, evacuating, and recharging with clean refrigerant to the correct level is the best method of achieving the correct refrigerant charge for the system. Charging the air conditioning system must be conducted by weighing refrigerant with a calibrated scale in order to ensure accuracy. Also, be sure to replace the oil which was removed during refrigerant recovery with new oil. Reference Service Manual, SENR5664, "Air Conditioning and Heating R134a for all Caterpillar Machines", "Refrigerant Compressor" for procedures regarding refrigerant charging and capacity of Caterpillar air conditioning systems.
Charge Level Checked? Yes or No.
Volume of Oil that was Removed During Recovery: ____ (ml) or (oz)
Weight of Refrigerant Charge: ____ (Kg) or (lbs)
2. Test for low pressure. The test for low pressure should be performed with ambient temperatures of less than 30 °C (86 °F). Park the machine in an area that is not in direct sunlight. Close all cab doors and windows. Block the flow of fresh air into the cab. If the air conditioning system is so equipped, bypass the low pressure switch . Start the machine. Operate the machine at high idle. Turn ON the air conditioning. Set the cab blower on LOW. After 10 to 15 minutes of operation, measure the low-side pressure at the refrigerant compressor. If the pressure reading is less than 69 kPa (10 psi) then the suction valves of the compressor are operating correctly.
Low Pressure Checked? Yes or No.
Low Pressure Reading: ____ (kPa) or (Psig)
Note: If the cab temperature is above 25 °C (77 °F), then the cab blower may need to be set to HIGH in order to reduce the temperature before starting the procedure.
3. Test for high pressure. Start the engine and set the speed at approximately 1200 rpm. Turn ON the air conditioning. Place a sheet of cardboard over the condenser in order to block the flow of air. Limiting the flow of air over the condenser will cause the discharge pressure of the compressor to increase. Check if the discharge of the compressor is able to increase up to 2414 kPa (350 psi). Once the specified pressure is reached, immediately remove the cardboard. If the compressor passes the test, the discharge valves are operating correctly.
High Pressure Checked? Yes or No.
High Pressure Reading: ____ (kPa) or (Psig)
4. The functional test is now complete. If this test procedure results in inconclusive results, your dealership's Technical Communicator can report the problem by using the on-line Dealer Solution Network. The Dealer Solution Network will provide your Technical Communicator with additional troubleshooting support.
5. Illustrations 1 through 4 are provided as Good Air Conditioning System Practices and Troubleshooting Tips.
