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 suppressers 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. This instruction show you guide on how to test air condition system electrical components for Caterpllar 924G wheel loader 3DZ.
All Caterpillar machine service manuals and EPC parts please refer to:2021 CAT SIS EPC+Service Manual Free Download
And for Caterpillar machine diagnostics,please use CAT ET 2022 Diagnostic Software
Procedures:
The following procedures are for testing pressure switches and arc suppresser components attached to the air conditioning system:
Equipment needed:
* 146-4080 Digital Multimeter, or similar digital multimeter with diode testing capability
* Multimeter Probe Kit
Testing 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 pressure
2.Closed Correct system pressure present
3.Open Indicating high system pressure
Positions 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: 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 Mulimeter 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 275kPa, and below 1750kPa, the meter will display less than 1 ohm.
5.If the resistance displayed is
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