Air Conditioning and Heating R-12 All Caterpillar Machines – Troubleshooting Heating and Air Conditioning Control System

------ WARNING! ------

Personal injury can result from contact with refrigerant.

This system is under pressure at all times, even if the engine is not running. Heat should never be applied to a charged system.

Contact with refrigerant can cause frost bite. Keep face and hands away to help prevent injury.

Protective goggles must always be worn when refrigerant lines are opened, even if the gauges indicate the system is empty of refrigerant.

Always use caution when a fitting is removed. Slowly loosen the fitting. If the system is still under pressure, evacuate the system recovering the refrigerant before removing the fitting.

Personal injury or death can result from inhaling refrigerant through a lit cigarette.

Inhaling air conditioner refrigerant gas through a lit cigarette or other smoking method or inhaling fumes released from a flame contacting air conditioner refrigerant gas, can cause bodily harm or death.

Do not smoke when servicing air conditioners or wherever refrigerant gas may be present.

Before any checks of the air conditioning and heating system are made, move the machine to a smooth horizontal surface. Lower all implements to the ground. Make sure the transmission is in neutral or park and that the parking brake is engaged. Keep all other personnel away from the machine or where they can be seen.

----------------------

Heating System

In order to conduct a performance check of the heating system, perform the following procedure.

  1. Run the engine at 1000 rpm.
  1. Adjust the temperature control knob to the setting for maximum heating.
  1. Put the fan switch in the HIGH position on heat.
  1. When the engine coolant temperature is in the normal operating range, the temperature of the air that is flowing from the louvers (air ducts) should be warm.

    If the temperature of the air that is flowing is not warm within 10 minutes of operation, refer to “Problem 2” section.

Problem 1

There is little warm air flow or no warm air flow when the heater control knob is set for maximum heating.

  1. Perform the following procedure:
    1. Check the engine coolant temperature. The temperature of the coolant must be at normal operating range.
    1. The heater control valve must be functioning properly. Check for the correct linkage adjustment from the temperature control lever to the heater control valve. The heater control valve must open completely when the temperature control knob is set for maximum heating.
    1. Check for blockage and check for bends in the heater hoses. Blockages and bends in the heater hoses would stop the flow of coolant through the system.
    1. Inspect the petcocks that connect the heater hoses to the engine block. Make sure that the petcocks are adjusted so that the petcocks are fully open.
  1. Make repairs to the components or replace any damaged component.

Electrical System

Problem 2

There is no flow to the operator’s compartment. The evaporator blower motors do not operate when the fan switch is activated.

  1. Perform the following procedure:
    1. Inspect the circuit breaker or inspect the fuses for an open circuit.
    1. Perform a visual inspection of all wire connections. Use the electrical schematic for the respective machine.
    1. Check for blockages at the fan blade.
    1. Check for the proper function of the fan switch at each setting. The evaporator blower motor will run at each setting. The evaporator blower motor should be operating in the cold mode and in the heating mode.
    1. Use a 5P-7277 Voltage Tester or use a 9U-7330 Multimeter in order to check the voltages in all components of the electrical system. Refer to the electrical schematic section for additional information for the machine.
  1. If necessary, make repairs or replace the components.

Test Procedure for Testing Electrical Components in the Air Conditioning System

The air conditioning systems on Caterpillar machines use pressure switches in order to protect the air conditioning system. Some air conditioning systems on Caterpillar machines use pressure switches and the on delay timer assembly for the refrigerant compressor in order to protect the air conditioning system. Arc suppressors protect other electrical components in the air conditioning system. Arc suppressors are applied in order 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    
146-4080     Digital Multimeter (RS-232)    

On Delay Timer Assembly for the Refrigerant Compressor Tests

In order to diagnose a faulty on delay timer assembly for the refrigerant compressor, the engine start switch must be in the ON position and the air conditioning switch activated.

Note: The on delay timer assembly will delay the power supply to the compressor clutch coil for 30 seconds after the air conditioning switch is activated.




Illustration 1 g00754249

(1) Output (signal voltage)

(2) Chassis ground

(3) Compressor clutch

(4) Power supply

  1. Separate the 4-pin connector from the wiring harness.
  1. Set the 146-4080 Digital Multimeter to DC voltage. Connect the positive probe to pin (4) on the wiring harness and connect the negative probe to a suitable ground. The multimeter should read 24 volts.

    Note: If the voltage is below 18 volts or the voltage is above 32 volts the on delay timer assembly will not supply power to the compressor.

  1. Set the 146-4080 Digital Multimeter to OHMS. Connect the positive probe to pin location (2) on the wiring harness and connect the negative probe to a suitable chassis ground. The multimeter will display OL if the ground is not present.
  1. Set the 146-4080 Digital Multimeter OHMS. Connect the positive probe to pin location (1) on the wiring harness and connect the negative probe to a suitable chassis ground. If the multimeter displays OL one of the three switches are open. Check each of the switches if an open condition occurs.

    Note: There must be refrigerant in the air conditioning system in order to close both of the pressure switches.

  1. In order to check that power is getting from the on delay timer assembly to the compressor clutch coil, reconnect the on delay timer assembly to the wiring harness. Set the 146-4080 Digital Multimeter to DC voltage. Remove the 2-pin connector from the compressor clutch coil. Connect the negative probe to a suitable chassis ground. Check each one of the two pins on the wiring harness for voltage. One of the two pins should supply 24 volts.
  1. In order to check the ground path from the compressor clutch coil to the chassis, turn off the air conditioning switch in the cab. Set the 146-4080 Digital Multimeter OHMS. Remove the 2-pin connector from the compressor clutch coil. Connect the negative lead to a suitable ground. Check each of the two pins on the 2-pin connectors for continuity. One of the two pins should display OL.
  1. If both the correct voltage and ground are present check the resistance of the compressor clutch coil. Refer to the Service Manual, SENR 3334, “Refrigerant Compressor” section in Specifications.

Pressure Switch Tests

Test Procedure for 114-5333 Pressure Switch and 114-5334 Pressure Switch (NORMALLY OPEN)

Pressure switches are used in order to protect the air conditioning compressor. The two most commonly used pressure switches are the 114-5333 Pressure Switch and the 114-5334 Pressure Switch. The only difference between the two 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 2 g00651406

Use the following procedures in order to test the pressure switch:

  1. Disconnect the pressure switch from the machine harness.
  1. Connect the 146-4080 Digital Multimeter to the two connector pins. Set the multimeter to the OHMS test mode.
  1. Measure the resistance of the pressure switch.
  1. 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.
  1. 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.
  1. When the pressure switch fails, test the arc suppressor for proper operation.
  1. 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 by vibration.

Note: The multimeter may display OL if the contacts on the pressure switch are dirty. The contacts on the pressure switch can become dirty if the arc suppressor is no longer functioning.

Note: The multimeter will display OL if the pressure switch is not threaded into the air conditioning system.

8T-8639 Low Pressure Switch (NORMALLY OPEN)



Illustration 3 g00651418
Table 3
Specifications for Pressure Switch    
Actuation Pressure (2)     344 ± 34 kPa (50 ± 5 psi)    
Deactuation Pressure (3)     172 ± 21 kPa (25 ± 3 psi)    
( 2 ) Close when pressure increases.
( 3 ) Open when pressure decreases.

Use the following procedures in order to test the pressure switch:

  1. Disconnect the pressure switch from the machine harness.
  1. Connect the 146-4080 Digital Multimeter to the two connector pins. Set the multimeter to the OHMS test mode.
  1. Measure the resistance of the pressure switch.
  1. If the system pressure is above 344 ± 34 kPa (50 ± 5 psi), the multimeter will display less than 1 ohm.
  1. If the resistance that is displayed is a value of OL (high resistance), and the system pressure is not below the acceptable limit, replace the pressure switch.
  1. When the pressure switch fails, test the arc suppressor for proper operation.
  1. 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 by vibration.

Note: The multimeter may display OL if the contacts on the pressure switch are dirty. The contacts on the pressure switch can become dirty if the arc suppressor is no longer functioning.

Note: The multimeter will display OL if the pressure switch is not threaded into the air conditioning system.

149-6371 Low Pressure Switch (NORMALLY OPEN)



Illustration 4 g00651452
Table 4
Specifications for Pressure Switch    
Actuation Pressure (2)     103 ± 14 kPa (15 ± 2 psi)    
Deactuation Pressure (3)     35 ± 7 kPa (5 ± 1 psi)    
( 2 ) Close when pressure increases.
( 3 ) Open when pressure decreases.

Use the following procedures in order to test the pressure switch:

  1. Disconnect the pressure switch from the machine harness.
  1. Connect the 146-4080 Digital Multimeter to the two connector pins. Set the multimeter to the OHMS test mode.
  1. Measure the resistance of the pressure switch.
  1. If the system pressure is above 103 ± 14 kPa (15 ± 2 psi), the multimeter will display less than 1 ohm.
  1. If the resistance that is displayed is a value of OL (high resistance), and the system pressure is not below the acceptable limit, replace the pressure switch.
  1. When the pressure switch fails, test the arc suppressor for proper operation.
  1. 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 by vibration.

Note: The multimeter may display OL if the contacts on the pressure switch are dirty. The contacts on the pressure switch can become dirty if the arc suppressor is no longer functioning.

Note: The multimeter will display OL if the pressure switch is not threaded into the air conditioning system.

3E-6462 High Pressure Switch (NORMALLY CLOSED)



Illustration 5 g00651464
Table 5
Specifications for Pressure Switch    
Actuation Pressure (4)     2400 ± 140 kPa (348 ± 20 psi)    
Deactuation Pressure (5)     1725 ± 100 kPa (250 ± 15 psi)    
( 4 ) Open when pressure increases.
( 5 ) Close when pressure decreases.

Note: A pressure switch that is NORMALLY CLOSED will open when the system pressure increases. The pressure switch will close when the system pressure decreases.

Use the following procedures in order to test the pressure switch:

  1. Disconnect the pressure switch from the machine harness.
  1. Connect the 146-4080 Digital Multimeter to the two connector pins. Set the multimeter to the OHMS test mode.
  1. Measure the resistance of the pressure switch.
  1. If the system pressure is below 2400 ± 140 kPa (348 ± 20 psi), the multimeter will display less than 1 ohm.
  1. If the resistance that is displayed is a value of OL (high resistance), and the system pressure is not above the acceptable limit, replace the pressure switch.
  1. When the pressure switch fails, test the arc suppressor for proper operation.
  1. 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 by vibration.

Note: The multimeter may display OL if the contacts on the pressure switch are dirty. The contacts on the pressure switch can become dirty if the arc suppressor is no longer functioning.

Note: The multimeter will display OL if the pressure switch is not threaded into the air conditioning system.

7X-1076 High Pressure Switch (NORMALLY CLOSED)



Illustration 6 g00651571
Table 6
Specifications for Pressure Switch    
Actuation Pressure (4)     2412 ± 140 kPa (350 ± 20 psi)    
Deactuation Pressure (5)     1723 ± 100 kPa (250 ± 15 psi)    
( 4 ) Open when pressure increases.
( 5 ) Close when pressure decreases.

Use the following procedures in order to test the pressure switch:

  1. Disconnect the pressure switch from the machine harness.
  1. Connect the 146-4080 Digital Multimeter to the two connector pins. Set the multimeter to the OHMS test mode.
  1. Measure the resistance of the pressure switch.
  1. If the system pressure is below 2412 ± 140 kPa (350 ± 20 psi), the multimeter will display less than 1 ohm.
  1. If the resistance that is displayed is a value of OL (high resistance), and the system pressure is not above the acceptable limit, replace the pressure switch.
  1. When the pressure switch fails, test the arc suppressor for proper operation.
  1. 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 by vibration.

Note: The multimeter may display OL if the contacts on the pressure switch are dirty. The contacts on the pressure switch can become dirty if the arc suppressor is no longer functioning.

Note: The multimeter will display OL if the pressure switch is not threaded into the air conditioning system.


Test Procedures for Arc Suppressors:

106-8704 Arc Suppressor



Illustration 7 g00651378

106-8704 Arc Suppressor

  1. Place the multimeter in the DIODE test mode.
  1. Place the red probe in the red terminal (positive terminal) of the multimeter.
  1. Place the black probe in the black terminal (negative terminal) of the multimeter.
  1. Place the red probe on Pin 2 of the connector on the arc suppressor. Place the black probe on Pin 1 of the connector.
  1. The multimeter should display a value between 0.5 VDC and 1.0 VDC.
  1. Place the red probe on Pin 1 of the connector on the arc suppressor. Place the black probe on Pin 2 of the connector on the arc suppressor.
  1. The multimeter should display OL.
  1. If the above conditions do not exist, the component should be considered faulty. The component will not provide adequate protection if the above conditions do not exist.
  1. Replace the component if the component has failed.

3E-9169 Arc Suppressor and 130-8134 Arc Suppressor



Illustration 8 g00651923

Arc Suppressor with Sure Seal Connectors

(1) Pin 1

(2) Pin 2



Illustration 9 g00651621

Arc Suppressor with DT Connectors

(1) Pin 1

(2) Pin 2

  1. Place the multimeter in the DIODE test mode.
  1. Place the red probe in the red terminal (positive terminal) of the multimeter.
  1. Place the black probe in the black terminal (negative terminal) of the multimeter.
  1. Place the red probe on Pin 1 of either connector on the arc suppressor. Place the black probe on Pin 2 of either connector.
  1. The multimeter should display a value between 0.5 VDC and 1.0 VDC.
  1. Place the red probe on Pin 2 of either connector of arc suppressor. Place the black probe on Pin 1 of either connector on the arc suppressor.
  1. The multimeter should display OFL or OL.
  1. Place the red probe on pin 1 of the female connector. Place the black probe on pin 1 of the male connector.
  1. The multimeter should have a reading of less than 0.01 VDC.
  1. Place the red probe on Pin 2 of the female connector. Place the black probe on Pin 2 of the male connector.
  1. The multimeter should have a reading of less than 0.01 VDC.
  1. The component is faulty if any of the conditions do not exist.
  1. If the component is faulty, replace the component.

105-8827 Arc Suppressor and 130-0956 Arc Suppressor



Illustration 10 g00651923

Arc Suppressor with Sure Seal Connectors

(1) Pin 1

(2) Pin 2



Illustration 11 g00651621

Arc Suppressor with DT Connectors

(1) Pin 1

(2) Pin 2

  1. Place the multimeter in the DIODE test mode.
  1. Place the red probe in the red terminal (plus terminal) of the multimeter.
  1. Place the black probe in the black terminal (negative terminal) of the multimeter.
  1. Place the red probe on Pin 1 of either connector on the arc suppressor. Place the black probe on Pin 2 of either connector.
  1. The multimeter should display a value between 0.5 VDC and 1.0 VDC.
  1. Place the red probe on pin 2 of either connector of arc suppressor. Place the black probe on pin 1 of either connector on the arc suppressor.
  1. The multimeter should display OFL or OL.
  1. Place the red probe on pin 1 of the female connector. Place the black probe on pin 1 of the male connector.
  1. The multimeter should have a reading of less than 0.01 VDC.
  1. Place the red probe on pin 2 of the female connector. Place the black probe on pin 2 of the male connector.
  1. The multimeter should have a reading of less than 0.01 VDC.
  1. The component is faulty if any of the conditions do not exist.
  1. If the component is faulty, replace the component.

Correct Mounting of Arc Suppressors

Certain arc suppressors may experience failure of the wire leads due to vibration if the arc suppressor is not properly supported.

Use a 2U-4497 Strap to tie-wrap the arc suppressor. The arc suppressor should be securely tie-wrapped to a stationary support in order to prevent any motion of the body of the arc suppressor. Additionally, the connectors on both ends of the arc suppressor should be secured.

A suitable bracket for supporting an arc suppressor is the 116-6100 Plate. The addition of a 9R-2926 Plate should permit the mounting of the 116-6100 Plate around obstacles. Use the 9R-2926 Plate if the 116-6100 Plate cannot be installed directly in an existing application.

The Sure Seal connectors on the 3E-9169 Arc Suppressor and the 105-8827 Arc Suppressor should be secured with two 9G-9150 Clips in order to prevent movement of the connectors relative to the body of the arc suppressor. The DT connectors on the 130-0956 Arc Suppressor and 130-8134 Arc Suppressor should be secured with two 9U-2297 Clips. The clips should be bolted through the slotted holes on the 116-6100 Plate .

The 106-8704 Arc Suppressor is an integral arc suppressor. The integral arc suppressor can be found on the newer machines. The 106-8704 Arc Suppressor is lighter than the other arc suppressors. The 106-8704 Arc Suppressor can be strapped directly to the wiring harnesses that are connected to the arc suppressor.

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