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. Troubleshooting the System with the Manifold Gauge Set
2.1. Troubleshooting Abnormal Noises

Troubleshooting the System with the Manifold Gauge Set



Illustration 1g00862735
Control Panel Type 1


Illustration 2g03342362
Control Panel Type 2
(1) Power switch
(2) Automatic temperature control switch
(3) Air conditioning override switch
(4) Temperature select switches
(5) Preset temperature display
(6) Fan speed switches
(7) Air outlet select switch
(8) Air inlet select switch
(9) Control panel
(10) Switch for defroster

The following conditions must exist in order to perform the checking procedures:

Engine ... Normal operating temperature
Door ... Open
Air inlet select switch (8) ... Recirculation
Temperature of air at inlet ... 30° to 35°C (86° to 95°F)
Fan speed switch (6) ... HI
Engine rpm ... 1500 rpm
Temperature select switch (4) ... MAX COOL

The following readings are correct under normal operating conditions.



Illustration 3g00475933

(L) Low-pressure side 0.15 to 0.25 MPa (22 to 36 psi)

(H) High-pressure side 1.37 to 1.57 MPa (200 to 230 psi)

Problem

The system has an insufficient amount of refrigerant charge.

Symptoms

  • Pressure is low on the low side and the high side.

  • Bubbles continuously appear in the sight glass.

  • The cooling effect is poor.

Cause

A refrigerant leak exists. This leak causes the amount of refrigerant charge to be low.

Corrective Measures

  1. Isolate the leak and repair the refrigerant leak.

  2. Recharge the air conditioning system. Refer to the Testing and Adjusting, "Refrigerant System - Charge" section for the proper procedure.

Problem

The system is overcharged with refrigerant, which causes poor cooling by the condenser.

Symptoms

  • Pressure is high on the low side and the high side.

  • Bubbles do not appear in the sight glass even when the system is operated slowly.

  • The cooling effect is poor.

Cause

The system is overcharged with refrigerant and the condenser is not cooling well.

Corrective Measures

  1. Recover the refrigerant until the level is correct. Refer to the Specifications, "System Capacities for Refrigerant" section for the proper amount of charge.

  2. Clean the condenser.

  3. Check the engine cooling fan.

Problem

Moisture is present in the refrigerant circuit.

Symptom

  • After a few minutes of use, the low-pressure side gradually indicates negative pressure.

Cause

Moisture has entered the refrigerant circuit.

Corrective Measures

  1. Replace the receiver-dryer. Refer to the Operation and Maintenance Manual, "Refrigerant Receiver-Dryer - Replace" section for the proper procedure.

  2. Evacuate the system. Refer to the Testing and Adjusting, "Refrigerant System - Evacuate" section for the proper procedure.

  3. Charge the system. Refer to the Testing and Adjusting, "Refrigerant System - Charge" section for the proper procedure.

Problem

The compressor is supplying insufficient compression.

Symptoms

  • The manifold gauge set shows excessive high pressure on the low side.

  • The high-pressure side measures pressure that is too low.

  • Pressure equalizes when the compressor is turned OFF.

Cause

The compressor is failing.

Corrective Measure

Check and repair the compressor.

Problem

The refrigerant does not circulate properly.

Symptoms

  • Negative pressure is indicated immediately on the low side when the system is completely clogged.

  • Negative pressure is indicated gradually on the low side when the system is sometimes clogged.

  • Air temperature is different before clogging and after clogging.

Cause

Debris collects around the small holes of the expansion valve. Another possibility is that moisture is freezing around the expansion valve.

Corrective Measures

  1. Replace the receiver-dryer. Refer to the Operation and Maintenance Manual, "Refrigerant Receiver-Dryer - Replace" section for the proper procedure.

  2. Evacuate the system. Refer to the Testing and Adjusting, "Refrigerant System - Evacuate" section for the proper procedure.

Problem

Air is present in the refrigerant circuit.

Symptoms

  • Pressure is high on both sides of the manifold gauge set.

  • The low-pressure lines are not cold.

  • Bubbles appear at the sight glass.

Cause

The refrigerant circuit contains air.

Corrective Measures

  1. Recover the refrigerant. Refer to the Testing and Adjusting, "Refrigerant Recovery" section for the proper procedure.

  2. Evacuate the system. Refer to the Testing and Adjusting, "Refrigerant System - Evacuate" section for the proper procedure.

  3. Charge the system. Refer to the Testing and Adjusting, "Refrigerant System - Charge" section for the proper procedure.

Problem

The expansion valve is not opening properly.

Symptoms

  • Pressure is high on both sides of the manifold gauge set.

  • The low-pressure lines are frosting.

Cause

The expansion valve is malfunctioning.

Corrective Measure

Make sure that the thermal tube is installed correctly.

Troubleshooting Abnormal Noises

Table 1
Troubleshooting Abnormal Noises 
Component  Possible Cause 
V-Belt  Tension is low. The belt is loose. 
Magnetic clutch  The bearing is worn or the bearing is damaged. 
Contact exists between the stator and the rotor.
Idle pulley  Incorrect installation 
The bearings are worn or the bearings are damaged.
Blower motor  Foreign material is obstructing proper movement. 
The blower is loose.
Compressor  A mounting bolt is loose. 
Valves are bad.
The bearing is worn or the bearing is damaged.
Misalignment
Refrigerant lines  Mounting clamps are loose or installed incorrectly. 
Incorrect gap for safety

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