307D, 311D, 312D, 313D, 315D, 318D, 319D, 320D, 323D, 324D, 325D, 326D, 328D, 329D, 330D, 336D, 340D, 345D, 349D, 374D, 390D and M325D Excavators Air Conditioning and Heating Air Conditioning System Troubleshooting Caterpillar


Air Conditioning System Troubleshooting
`
1.1. Poor Cooling
2.2. Air flow is short
3.2. The blower motor rotates
4.3. Diagnostics
5.2. The blower motor does not rotate
6.3. Diagnostics
7.2. Normal air flow
8.2. Compressor rotation is normal.
9.2. Pressure is normal
10.3. Diagnostics
11.2. Pressure is abnormal
12.3. Diagnostics
13.2. Compressor rotation is abnormal
14.3. Diagnostics
15.1. Specifications

Poor Cooling

If the air flow is normal, see "Normal air flow". If the air flow is short, see "Air flow is short".

Air flow is short

If the blower motor rotates, refer to "The blower motor rotates". If the blower motor does not rotate, see "The blower motor does not rotate".

The blower motor rotates

Diagnostics

  1. If the rotation is correct, see steps 2, 3, 4, 5, 6, and 8. If the rotation is slow, see steps 9, 10, 11, and 12.

  2. If the recirculation filter is clogged, clean the filter.

  3. If the fresh air filter is clogged, clean the filter.

  4. If an obstacle is logged at the inlet port, remove the obstacle.

  5. If the blower motor is distorted or broken, replace the blower motor.

  6. If the evaporator is frosted and there is voltage that is applied to the magnetic clutch, see 7. If the evaporator is frosted and there is no voltage that is applied to the magnetic clutch, the magnetic clutch is poor. Replace the magnetic clutch.

  7. Check the clutch circuit. If necessary, replace the clutch relay. Check the wiring of the frost sensor for a short. If necessary, repair the wiring. Check the characteristics of the frost sensor. If necessary, replace the frost sensor. Check the gap between the frost sensor and the evaporator. If necessary, adjust the distance for the gap. See "Specifications".

  8. If there is debris on the evaporator surface, clean the surface.

  9. If power voltage drops, check the battery or check the charging surface.

  10. If there is poor contact with the battery terminal, repair the terminal.

  11. If the blower motor is poor, replace the motor.

  12. If the blower high relay is poor, replace the relay.

The blower motor does not rotate

Diagnostics

  1. If the blower motor rotates only in the HI speed, see step 2. If the blower motor does not rotate in the HI, or Lo speeds, see steps 3, 4, 5, 6, 7, 8, and 9.

  2. If the resistor has an open circuit, replace the resistor.

  3. If a fuse has an open circuit, repair the fuse.

  4. If the power up relay of the vehicle is poor, replace the relay.

  5. If the blower motor is poor, replace the motor.

  6. If the blower motor is in contact with the case, repair the motor.

  7. If the blower switch is poor, replace the switch.

  8. If the body ground is poor, repair the ground.

  9. If the wiring is poor, repair the wiring.

  10. If the power transistor is poor, replace the transistor.

Normal air flow

If the compressor rotation is normal, see "Compressor rotation is normal.". If the compressor rotation is abnormal, see "Specifications".

Compressor rotation is normal.

If the pressure is normal, see "Pressure is normal". If the pressure is abnormal, see "Pressure is abnormal".

Pressure is normal

Diagnostics

  1. If fresh air is entering the cab, see steps 2 and 3. If the temperature control is poor, see step 4. If hot water from the heater is being circulated through the system, see step 5.

  2. Close the window or close the door.

  3. Adjust the damper for recirculation.

  4. Check the actuator for temperature control. If necessary, replace the actuator. Check damper operation. If necessary, replace the damper.

  5. Check the actuator for temperature control. If necessary, replace the actuator. Check the water valve. If necessary, replace the water valve.

Pressure is abnormal

Diagnostics

  1. If high side pressure is abnormally high, see steps 2, 3, 4, and 5. If low side pressure is abnormally high, see steps 4, 6, and 7. If high side pressure is abnormally low, see 8, 9, 10, and 11. If low pressure is abnormally low, see 8, 9, 11, 12, and 13. If the high side pressure is high and the low side pressure is high, see steps 3, and 4. If the high side pressure is low and the low side pressure is low, see step 15.

  2. If the outside temperature is abnormally high, there is an insufficient amount of cooling.

  3. If the condenser is not being cooled, the condenser could be clogged. Clean the condenser with water.

  4. If the refrigerant is overcharged, remove the fluid until the correct level is obtained.

  5. If the air is mixed in the freezing cycle, evacuate the refrigerant. Refill the refrigerant to the correct level.

  6. If the compression is poor, check the gasket at the head of the compressor for breakage. If necessary, replace the compressor. Check if the suction valve is broken or clogged. If necessary, replace the compressor.

  7. If the expansion valve opens too much, the valve could be poor. Replace the valve. Contact with the thermal tube could be poor. Repair the thermal tube.

  8. The outside temperature is abnormally low.

  9. If the refrigerant is low, there could be an insufficient refrigerant charge. Recharge the refrigerant to the correct level. If the refrigerant is low, there could be a gas leak. Perform the leak and the repair test. Recharge the refrigerant to the correct level.

  10. If the compressor is poor, the shoe for the cam plate could be locked. The piston could be locked. The suction valve could be poor and the delivery valve could be poor. Replace the compressor if anyone of the problems exists.

  11. If the expansion valve is poor, the valve could be clogged. The thermal tube could have a gas leak. Replace the valve. If the expansion valve is poor, the expansion valve is frozen. Replace the valve and the receiver. Evacuate the valve completely.

  12. If the receiver and the dryer are clogged repair the system. If the piping is clogged with debris, repair the system.

  13. If the evaporator is frosted and there is voltage that is applied to the magnetic clutch, see 14. If the evaporator is frosted and there is no voltage that is applied to the magnetic clutch, the magnetic clutch is poor. Replace the magnetic clutch.

  14. Check the clutch circuit. If necessary, replace the clutch relay. Check the wiring of the frost sensor for a short. If necessary, repair the wiring. Check the characteristics of the frost sensor. If necessary, replace the frost sensor. Check the gap between the frost sensor and the evaporator. If necessary, adjust the distance of the gap. See "Specifications".

  15. The refrigerant is poor. Replace the system.

Compressor rotation is abnormal

Diagnostics

  1. If the electrical system and the clutch do not function, check the wiring and see steps 2, 3, 4, 5, 6, and 7. If the magnetic clutch is poor, see steps 17, 18, 19, and 20. If the V-belt is worn or the V-belt slips replace the belt. If the compressor is locked up, replace the compressor.

  2. If the air conditioning switch is poor, replace the control panel.

  3. If the blower switch is poor, replace the control panel.

  4. If the clutch relay on the compressor is poor, replace the clutch relay.

  5. If the thermo-sensor is poor, replace the thermo-sensor.

  6. If the high and low pressure switch is poor replace the pressure switch.

  7. If high pressure is abnormally high, see steps 8, 9, 10, and 11. If high pressure is abnormally low, see steps 12, 13, 14, 15, and 16.

  8. If the outside temperature is abnormally high there is an insufficient amount of cooling.

  9. If the condenser is not being cooled, the condenser could be clogged. Clean the condenser with water.

  10. If the refrigerant is overcharged remove the fluid until the correct level is obtained.

  11. If the air is mixed in the freezing cycle, evacuate the refrigerant. Refill the refrigerant to the correct level.

  12. The outside temperature is abnormally low.

  13. If the refrigerant is low there could be an insufficient refrigerant charge. Recharge the refrigerant to the correct level. If the refrigerant is low there could be a gas leak. Perform the leak and the repair test. Recharge the refrigerant to the correct level.

  14. If the receiver and the dryer are clogged repair the system. If the piping is clogged with debris, repair the system.

  15. If the expansion valve is poor the valve could be clogged. The thermal tube could have a gas leak. Replace the valve. If the expansion valve is poor, the expansion valve is frozen. Replace the valve and the receiver. Evacuate the valve completely.

  16. Check the clutch circuit. If necessary, replace the clutch relay. Check the wiring of the frost sensor for a short. If necessary, repair the wiring. Check the characteristics of the frost sensor. If necessary, replace the frost sensor. Check the gap between the frost sensor and the evaporator. If necessary, adjust the distance of the gap. See "Specifications".

  17. If there is an open circuit in the stator coil replace the clutch.

  18. If the air gap is too much between the rotor and the stator replace the clutch or repair the clutch.

  19. If the clutch rattles check the key for breakage. If necessary, replace the key. Check the clutch surface for contamination. If necessary, replace the clutch. Check the battery for a voltage drop. If necessary, charge the battery.

  20. If there is debris that is trapped between the rotor and the stator, disassemble the clutch and repair the clutch.

Specifications

Check the distance of the gap between the frost sensor and the evaporator. ... 12 to 5 mm (0.472 to 0.197 inch)

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