BRACKET-THROTTLE 2655625 - Caterpillar

Test Procedure for Testing Electrical Components in the Air Conditioning System
The air conditioning systems on Cat machines use pressure switches to protect the air conditioning system. Some air conditioning systems on Cat machines use pressure switches and on delay timer assembly for the refrigerant compressor to protect the air conditioning system. Arc suppressors protect other electrical components in the air conditioning system. Arc suppressors are applied to discharge electrical inductance when the compressor disengages. Failure of the arc suppressor can affect the reliability of the pressure switch. Failure of the arc suppressor may cause failure of the pressure switch.The following procedures are for the testing of the on delay timer assembly, pressure switches, and components of the arc suppressor.
Table 1
Required Tools
Part Number Part Description
257-9140 Digital Fluke (Fluke 87V Multimeter) Pressure Switch Tests
Test Procedure for 114-5333 Pressure Switch / 355-3148 Pressure Switch and 114-5334 Pressure Switch (NORMALLY OPEN)
Pressure switches are used in order to protect the a/c compressor. The three most commonly used pressure switches are the 114-5333 Pressure Switch / 355-3148 Pressure Switch and the 114-5334 Pressure Switch. The only difference between the three switches is the connector. Only one of these switches is used per machine. The high pressure and low-pressure switches have three possible switch positions which are given below:OPEN - System pressure is low.CLOSED - System pressure is correct.OPEN - System pressure is high.The two OPEN positions of the pressure switch protect the air conditioning system. The OPEN position prevents the compressor from actuating when potentially harmful pressures exist in the system. The CLOSED position is the normal operating switch position. The following table contains the logic for the pressure switches:
Table 2
Pressure Range Contact Position (Pressure Rise) Contact Position (Falling Pressure)
High Position 3 Above 2800 kPa (406 psi) OPEN OPEN
Hysteresis Band(1) 1750 kPa (254 psi) to 2800 kPa (406 psi) CLOSED OPEN
Middle (Position 2) 275 kPa (40 psi) to 1750 kPa (254 psi) CLOSED CLOSED
Hysteresis Band(1) 170 kPa (25.0 psi) to 275 kPa (40 psi) OPEN CLOSED
Low Position 1 0 kPa (0 psi) to 170 kPa (25.0 psi) OPEN OPEN
(1) Pressure must pass through the hysteresis band in order to provide the correct conditions for the switch contact.
Illustration 5 g00651406Use the following procedures in order to test the pressure switch:
Disconnect the pressure switch from the machine harness.
Connect the 257-9140 Digital Multimeter to the two connector pins. Set the multimeter to the OHMS test mode.
Measure the resistance of the pressure switch.
If the system pressure is between 275 kPa (40 psi) and 1750 kPa (254 psi), the multimeter will display a value that is less than 1 ohm.
If the resistance that is displayed is a value of OL (high resistance), and the system pressure is within acceptable limits, replace the pressure switch.
When the pressure switch fails, test the arc suppressor for proper operation.
If the pressure switch is removed, make sure that the wires on the new pressure switch are tie-wrapped. Securing the pressure switch prevents damage that may be caused