CUP-DUST 1726423 - Caterpillar

All Machines with Air Conditioned CabsDescription of Change: The air conditioning systems on Caterpillar Inc. machines use pressure switches to protect the air conditioning compressor. To further protect other electrical components in the air conditioning system, arc suppressors are applied to discharge inductive loads when the compressor de-actuates. Arc suppressor failure can affect the reliability of the pressure switch, and cause it to fail. The following procedures are for testing pressure switches and arc suppressor components attached to the air conditioning system:
Equipment Needed:
* 146-4080 Digital Multimeter, or similar digital multimeter with diode testing capability* Multimeter Probe KitTesting Pressure Switches:
114-5333 And 114-5334 High/Low Pressure Switches (NORMALLY OPEN)
In general, the two pressure switches used to protect the air conditioning compressor on Caterpillar machines are part numbers 114-5333, and 114-5334. The only difference in these switches is the connector. Functionally, they are the same. Only one of these is used per machine. These high/low pressure switches have three potential switch positions. These positions are:
1. Open Indicating low system pressure2. Close Correct system pressure present3. Open Indicating high system pressurePositions 1 and 3 protect the air conditioning system by preventing the compressor from actuating when potentially harmful pressure conditions exist. Position 2 is the normal operating switch position.
The following table details the pressure switch logic of these two switches:
Note A: Pressure must pass through the hysteresis band to provide correct contact condition.
To test the switch:
1. Disconnect the switch from the machine harness.2. Connect the 146-4080 Multimeter to the two connector pins, and place the meter in the Ohms position.3. Measure the switch resistance.4. If the system is charged to above 275 kPa, and below 1750 kPa, the meter will display less than 1 ohm.5. If the resistance displayed is "OL" (high resistance), and the system pressure is within acceptable limits, replace the switch.6. Every time the switch fails, also test for arc suppressor functionality.7. If the switch is removed, ensure the new switch wires are securely cable-wrapped to prevent vibration damage. The meter can display "OL" if the switch contacts are dirty. The switch contacts can become dirty if the arc suppressor is no longer functioning. The meter