785G Off-Highway Truck/Tractor Electrical and Hydraulic Systems Caterpillar

Note: Refer to the Testing and Adjusting, UENR4125, "Machine Preparation for Testing and Adjusting" section before service work is performed on the air conditioning system.

Problem Solving

The following problem-solving section is provided to identify and correct problems that may occur in the air conditioning system. Several problems can have the same system condition or similar system conditions. Before starting the procedure to correct these problems, be complete in the diagnosis of the problems.

The problem-solving procedures are based on the system condition during the problem. To indicate the system pressures, the manifold gauge set must be installed. The manifold gauge set is only used to diagnose problems. The refrigerant lines can give an indication of system operation that is abnormal. Temperature differences between the high-pressure side and the low-pressure side can be an indication of abnormal operation in a line. This problem can also be found by cold spots (frost) on the line. In R134a air conditioning systems, the lines can have spots of frost and the system can be operating normally. Frost will most often form after the orifice and on the lower portion of the accumulator. The temperature of the air flow from the evaporator will also indicate a problem with the system. Knowing the complete system condition is an important step in making a correct diagnosis.

Note: R134a air conditioning system problem diagnosis requires a combination of symptoms or indicators to identify and solve problems correctly.

Problem-Solving Procedure

1. Install the manifold gauge set. Refer to the Testing and Adjusting, UENR4125, "Manifold Gauge Set (Refrigerant) - Install" section in Testing and Adjusting.

2. Run the engine at 1000 rpm. Put the air conditioner temperature control knob at Maximum COOL position. Put the fan switch at HIGH position on the AIR CONDITIONING side. To stabilize the system, operate the engine for a minimum of 10 minutes.

3. Adjust the engine speed to approximately 1300 rpm to 1400 rpm. Record the readings on the low-pressure gauges and the high-pressure gauges. The gauge readings will be a partial indication of the system condition.

4. Compare the discharge and suction pressures on the manifold gauge set to the Pressure Ranges that are in Table 1. Determine if the system is functioning correctly for the current ambient temperature. Use the table to determine if the system is operating normally. If the pressures are high or the pressures are low, refer to the system conditions listed in "Refrigerant Circuit Problems" table.

   During normal operation of the air conditioning system in 21 °C (70 °F) weather, the discharge pressure will be 820 kPa (119 psi) to 1300 kPa (189 psi).

   The pressure on the suction side will be 70 kPa (10 psi) to 130 kPa (19 psi).

   The outside temperature and humidity effects pressure. If the outside temperature is high, the discharge pressure will be high. In hot weather, the suction and the discharge pressures will be high. In cooler weather, the suction and the discharge pressure will be normal or the pressure can be lower.

   Note: All pressures are given as a guide only. Weight is the only absolute means of determining proper refrigerant charge. Improper refrigerant charge will cause premature failure of the compressor.

   Show/hide table

   Table 1

   Pressure Range (1)
   Ambient Air Temperature C° (F°)	High-pressure Test Fitting kPa (psi)(2)(3)	Low-pressure Test Fitting kPa (psi)(4)(5)(6)
   21°C (70°F)	820 kPa to 1300 kPa (119 psi to 190 psi)	70 kPa to 138 kPa (10 psi to 20 psi)
   27°C (80°F)	950 kPa to 1450 kPa (138 psi to 210 psi)	70 kPa to 173 kPa (10 psi to 25 psi)
   32°C (90°F)	1175 kPa to 1650 kPa (170 psi to 240 psi)	105 kPa to 210 kPa (15 psi to 30 psi)
   38°C (100°F)	1300 kPa to 1850 kPa (189 psi to 268 psi)	105 kPa to 210 kPa (15 psi to 30 psi)
   43°C (110°F)	1450 kPa to 2075 kPa (210 psi to 300 psi)	105 kPa to 210 kPa (15 psi to 30 psi)

   Show/hide table

   (1)	This table is only for reference.
   (2)	Pressure may be slightly higher in humid conditions and lower in dry conditions.
   (3)	The AC High-pressure Test Fitting is located near the Evaporator Inlet. The pressure reading will be 83 kPa to 103 kPa (12 psi to 15 psi) lower.
   (4)	Pressure before clutch disengagement.
   (5)	The AC Low-pressure Test Fitting is located near the Evaporator Outlet. The pressure reading will be 14 kPa to 21 kPa (2 psi to 3 psi) higher.
   (6)	The AC Low-pressure Test Fitting is located near the Evaporator Inlet. The pressure reading will be in the range of 138 kPa (20 psi) higher.

Indications from the Compressor Pressures

Use Table 2 to diagnose indications from the pressures.

Refrigerant Circuit Problems

There is no or only little cool temperature to the air flow from the evaporator.

System Condition 1

1. Low-pressure gauge reading is below normal. For normal operating pressures, refer to Table 1.

2. High-pressure gauge reading is below normal. For normal operating pressures, refer to Table 1.

   Note: Ambient temperature is above 21°C (70°F).

3. From the evaporator, the temperature of the air flow is partially cool.

Probable Cause

Leaks in the refrigerant circuit will cause the system to be low on refrigerant.

• Perform a leak test. refer to the Testing and Adjusting, UENR4125, "Refrigerant Leakage - Test" section in Testing and Adjusting.

• If leaks are found, recover the refrigerant. Refer to the Testing and Adjusting, UENR4125, "Refrigerant Recovery" section.

• Repair leaks.

• If a large amount of refrigerant was lost, fill the compressor.

• Perform a partial charge of the system.

• Evacuate the system. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Evacuate" section in Testing and Adjusting.

• Charge the system with the correct amount of refrigerant. Measure the refrigerant by weight. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Charge" section in Testing and Adjusting.

• After the system is charged and operated for a minimum of 10 minutes, perform a performance check. Testing and Adjusting, UENR4125, "Air Conditioning Performance - Test".

System Condition 2

1. Low-pressure gauge reading is normal. For normal operating pressures, refer to Table 1.

2. High-pressure gauge reading bounces or the reading is unsteady.

Probable Cause

Air is in the system.

• Reclaim the refrigerant from the air conditioning system.

• Evacuate the air conditioning system.

• Recharge the air conditioning system.

System Condition 3

1. Low-pressure gauge reading is below normal. For normal operating pressures, refer to Table 1.

2. High-pressure gauge reading is above normal. For normal operating pressures, refer to Table 1.

   Note: Ambient temperature is above 21°C (70°F).

3. The temperature of the air flow from the evaporator is warm.

Probable Cause

Air or moisture (water) in the system.

• Recover the refrigerant. Refer to the Testing and Adjusting, UENR4125, "Refrigerant Recovery" section.

• Replace the receiver-dryer or the in-line dryer. The desiccant may be full of moisture. This condition will release water into the system. Refer to the Disassembly and Assembly, UENR4125, "Receiver-Dryer - Remove and Install" section. For in-line dryers, refer to the Disassembly and Assembly, UENR4125, "In-Line Refrigerant Dryer - Remove and Install" section.

• Evacuate the system. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Evacuate" section.

• Charge the system with the correct amount of refrigerant. Measure the refrigerant by weight. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Charge" section in Testing and Adjusting.

• After the system is charged and operated for a minimum of 10 minutes, perform a performance check. Testing and Adjusting, UENR4125, "Air Conditioning Performance - Test".

System Condition 4

1. Low-pressure gauge reading is below normal. For normal operating pressures, refer to Table 1.

2. High-pressure gauge reading is normal to the below normal range. For normal operating pressures, refer to Table 1.

   Note: Ambient temperature is above 21°C (70°F).

3. The temperature of the air flow from the evaporator is partially cool.

4. The high side liquid line or the receiver-dryer is frosted. The high side liquid line or the receiver-dryer is cool to the touch.

Probable Cause

Restriction in the high-pressure liquid line can cause the refrigerant to be removed from the evaporator at a faster rate. The restriction can cause the evaporator to be low on refrigerant from the receiver-dryer or from the in-line dryer. Clogged filters or a failure of the blower motor can cause possible restrictions to the air flow.

• Recover the refrigerant. Refer to the Testing and Adjusting, UENR4125, "Refrigerant Recovery" section.

• If the restriction is found at the receiver-dryer, replace the receiver-dryer. Refer to the Disassembly and Assembly, UENR4125, "Receiver-Dryer - Remove and Install" section in Disassembly and Assembly.

• If the restriction is found at the in-line dryer, replace the in-line dryer.

• If the restriction is found at the liquid line, replace the liquid line.

• Cap all the open lines and fittings.

Note: Restrictions of the refrigerant flow are identified by frost or cold spots in the line. Also, restrictions of the refrigerant flow are identified by frost or cold spots in the receiver-dryer or the in-line dryer.

• Replace filters or remove any of the restrictions.

• Evacuate the system. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Evacuate" section in Testing and Adjusting.

• Charge the system with the correct amount of refrigerant. Measure the refrigerant by weight. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Charge" section in Testing and Adjusting.

• After the system is charged and operated for a minimum of 10 minutes, perform a performance check. Testing and Adjusting, UENR4125, "Air Conditioning Performance - Test".

System Condition 5

Note: The system only cools the cab in the morning and in the evening. The system does not cool the cab during the hot part of the day.

1. Low-pressure gauge reading is normal, but the gauge reading may drop into the vacuum range during the testing procedure. For normal operating pressures, refer to Table 1.

2. The high-pressure gauge reading is normal. But the gauge reading is below normal when the low-pressure gauge drops into the vacuum range. For normal operating pressures, refer to Table 1.

   Note: Ambient temperature is above 21°C (70°F).

3. Air flow from the evaporator is cold, but the air flow will become warm when the low-pressure gauge drops into vacuum.

Probable Cause

The system has a large amount of moisture. The desiccant in the receiver-dryer or the in-line dryer is full of water. The water is released during high ambient temperatures. Ice collects in the orifice or the expansion valve and the ice can block the flow of refrigerant.

• Recover the refrigerant from the system. Refer to the Testing and Adjusting, UENR4125, "Refrigerant Recovery" section.

• Replace the receiver-dryer or the in-line dryer. Refer to the Disassembly and Assembly, UENR4125, "Receiver-Dryer - Remove and Install" section in Disassembly and Assembly. For in-line dryers, refer to the Disassembly and Assembly, UENR4125, "In-Line Refrigerant Dryer - Remove and Install" section.

• Remove the moisture from the system. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Evacuate" section.

• Charge the system with the correct amount of refrigerant. Measure the refrigerant by weight. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Charge" section.

• After the system is charged and operated for a minimum of 10 minutes, perform a performance check. Refer to Testing and Adjusting, UENR4125, "Air Conditioning Performance - Test".

Note: Low-pressure (suction) drops into vacuum when ice forms in the expansion valve. High-pressure (discharge) drops when low-pressure drops into vacuum.

System Condition 6

1. The low-pressure gauge reading does not change. The pressure should rise when the compressor is not in operation. For normal operating pressures, refer to Table 1.

2. High-pressure gauge reading is at the high end of the normal range.

   Note: Ambient temperature is above 21°C (70°F).

3. The temperature of the air flow from the evaporator is partially cool.

Probable Cause

The system has air or moisture in the system. The system does not have a full charge of refrigerant.

• Perform a leak test and carefully test around the compressor seal. Refer to the Testing and Adjusting, UENR4125, "Refrigerant Leakage - Test" section.

• Recover the refrigerant from the system. Refer to the Testing and Adjusting, UENR4125, "Refrigerant Recovery" section.

• Repair leaks.

• Check the compressor for loss of oil.

• Evacuate the system. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Evacuate" section.

• Charge the system with the correct amount of refrigerant. Measure the refrigerant by weight. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Charge" section.

• After the system is charged and operated for a minimum of 10 minutes, run a performance check. Refer to Testing and Adjusting, UENR4125, "Air Conditioning Performance - Test".

System Condition 7

1. Low-pressure gauge reading is above normal. For normal operating pressures, refer to Table 1.

2. High-pressure gauge reading is above normal. For normal operating pressures, refer to Table 1.

   Note: Ambient temperature is above 21°C (70°F).

3. High-pressure (liquid line) is hot.

4. The compressor may become noisy and the drive belt may slip.

   Note: The compressor is not operating under ambient temperatures that are extreme. The compressor is not operating under high humidity that is extreme.

Probable Cause

The system is overcharged.

• Recover the remaining refrigerant. Refer to the Testing and Adjusting, UENR4125, "Refrigerant Recovery" section.

• Charge the system with the correct amount of refrigerant. Measure the refrigerant by weight. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Charge" section in Testing and Adjusting.

• Perform a performance check. Refer to Testing and Adjusting, UENR4125, "Air Conditioning Performance - Test".

Note: Perform the following procedure if the system has not been serviced for an extended period. Perform the following procedure if the pressures of the system are not within the correct specifications.

• Recover the refrigerant. Refer to the Testing and Adjusting, UENR4125, "Refrigerant Recovery" section.

• Evacuate the system. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Evacuate" section. If service work has not been performed for an extended period, replace the receiver-dryer or the in-line dryer.

• Charge the system with the correct amount of refrigerant by weight. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Charge" section.

• After the system is charged and operated for a minimum of 10 minutes, perform a performance check. Refer to Testing and Adjusting, UENR4125, "Air Conditioning Performance - Test".

System Condition 8

1. Low-pressure gauge reading is above normal. For normal operating pressures, refer to Table 1.

2. High-pressure gauge reading is below normal. For normal operating pressures, refer to Table 1.

   Note: Ambient temperature is above 21°C (70°F) and the system has a refrigerant charge that is full.

3. The temperature of the air flow from the evaporator is partially cool.

Probable Cause

The compressor has internal leaks. The reed valve has leakage. The compressor piston, rings, or cylinders are worn.

• Check the compressor drive belt for the correct tension.

• Perform a leak test. Isolate the problem to the compressor. Refer to the Testing and Adjusting, UENR4125, "Refrigerant Leakage - Test" section.

If an internal leak is found, perform the following procedure.

• Replace the compressor. Refer to the Disassembly and Assembly, UENR4125, "Refrigerant Compressor - Remove and Install" section.

• Replace the receiver-dryer. Refer to the Disassembly and Assembly, UENR4125, "Receiver-Dryer - Remove and Install" section in Testing and Adjusting.

• Evacuate the system. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Evacuate" section.

• Charge the system with the correct amount of refrigerant by weight. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Charge" section.

• After the system is charged and operated for a minimum of 10 minutes, perform a performance check. Refer to Testing and Adjusting, UENR4125, "Air Conditioning Performance - Test".

If an external leak such as a hose connection is found, perform the following procedure.

• Recover the refrigerant. Refer to the Testing and Adjusting, UENR4125, "Refrigerant Recovery" section.

• Repair leaks.

If a large amount of refrigerant is lost, check the compressor for the loss of oil.

• Evacuate the system. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Evacuate" section.

• Charge the system with the correct amount of refrigerant. Measure the refrigerant by weight. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Charge" section.

• After the system is charged and operated for a minimum of 10 minutes, perform a performance check. Refer to Testing and Adjusting, UENR4125, "Air Conditioning Performance - Test".

System Condition 9

1. Low-pressure gauge reading is above normal. For normal operating pressures, refer to Table 1.

2. High-pressure gauge reading is normal or low. For normal operating pressures, refer to Table 1.

   Note: Ambient temperature is above 21°C (70°F) and the system has a refrigerant charge that is full.

3. The temperature of the air flow from the evaporator is warm.

4. The suction hose and the evaporator are covered with moisture (sweating).

Probable Cause

Replace the expansion valve.

To ensure that the system operates correctly, perform a performance check. Refer to Testing and Adjusting, UENR4125, "Air Conditioning Performance - Test".

Illustration 1	g00409166
Expansion valve in the open position (Typical Example) (1) Capillary tube (2) Expansion valve diaphragm chamber (3) Inlet (4) Outlet

System Condition 10

1. Low-pressure gauge reading is too low. For normal operating pressures, refer to Table 1.

2. High-pressure gauge reading is too low. For normal operating pressures, refer to Table 1.

   Note: Ambient temperature is above 21°C (70°F).

3. The temperature of the air flow from the evaporator is partially cool or warm.

4. Moisture (water) or frost is on the expansion valve inlet or orifice tube assembly.

Probable Cause

The problems that are described in Step 1 through Step 4 can be caused by the following faults:

Note: The following faults will cause a restriction of the flow of refrigerant to the evaporator.

• Improper operation of the expansion valve (stuck valve).

• Blockage at the evaporator inlet.

• No charge in temperature sensing bulb.

Note: The inlet to the expansion valve will be warm during normal operation.

1. Replace the expansion valve.

   Note: The sensing bulb must be installed correctly to ensure the correct operation of the expansion valve. Clean the location for the sensing bulb with steel wool or emery paper. Use a 8P-6355 Clip to attach the sensing bulb securely to the evaporator coil outlet pipe. Completely cover the assembly with 5P-7070 Strip Insulation.

   Replace the expansion valve.

   • Evacuate the system. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Evacuate" section.

   • Charge the system with the correct amount of refrigerant. Measure the refrigerant by weight. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Charge" section.

   • After the system is charged and operated for a minimum of 10 minutes, perform a performance check. Refer to Testing and Adjusting, UENR4125, "Air Conditioning Performance - Test".

2. Replace the in-line dryer or replace the orifice tube.

   • Evacuate the system. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Evacuate" section.

   • Charge the system with the correct amount of refrigerant. Measure the refrigerant by weight. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Charge" section.

   • After the system is charged and operated for a minimum of 10 minutes, perform a performance check. Refer to Testing and Adjusting, UENR4125, "Air Conditioning Performance - Test".

Illustration 2	g00415456
Expansion valve in the closed position (Typical Example) (1) Capillary tube (2) Expansion valve diaphragm chamber (3) Inlet (4) Outlet

Note: For expansion valve systems, refer to Step 1. For orifice tube systems, refer to Step 2.

System Condition 11

1. Low-pressure gauge reading is too high. For normal operating pressures, refer to Table 1.

2. High-pressure gauge reading is too high. For normal operating pressures, refer to Table 1.

   Note: Ambient temperature is above 21°C (70°F).

3. The temperature of the air flow from the evaporator is warm.

Probable Cause

The condenser is not functioning properly.

Note: The system may have a normal or overcharge of refrigerant.

1. Check for a blockage in the flow of air through the condenser.

2. If a blockage is found in the condenser, remove all blockages and perform a performance check. The performance check will ensure proper system operation. Refer to Testing and Adjusting, UENR4125, "Air Conditioning Performance - Test".

3. If the problem still exists, perform the following procedure. Check the system for an overcharge of refrigerant.

   Note: Do not operate the engine.

   • Recover the refrigerant. Refer to the Testing and Adjusting, UENR4125, "Refrigerant Recovery" section.

   • Evacuate the system. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Evacuate" section.

   • Recharge the system with the correct amount of refrigerant. Measure the refrigerant by weight. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Charge" section.

   Note: With the ambient temperature above 21°C (70°F), the normal gauge reading for the low-pressure side is 70 kPa to 138 kPa (10 psi to 20 psi) when the normal gauge reading for the high-pressure side is 820 kPa to 1300 kPa (119 psi to 189 psi).

   • To ensure the correct systems operation, perform a performance check. Refer to Testing and Adjusting, UENR4125, "Air Conditioning Performance - Test".

4. If the low-pressure gauge reading and the high-pressure gauge readings are too high, perform the following procedure:

   • Recover the refrigerant from the system. Refer to the Testing and Adjusting, UENR4125, "Refrigerant Recovery" section.

   • Replace the receiver-dryer or replace the in-line dryer. Refer to the Disassembly and Assembly, UENR4125, "Receiver-Dryer - Remove and Install" section. For in-line dryers, refer to the Disassembly and Assembly, UENR4125, "In-Line Refrigerant Dryer - Remove and Install" section in Disassembly and Assembly.

   • If the receiver-dryer or the in-line dryer is not equipped with quick couplers, evacuate the system. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Evacuate" section.

   • Charge the system with the correct amount of refrigerant. Measure the refrigerant by weight. Refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Charge" section in Testing and Adjusting.

   • After the system is charged and operated for a minimum of 10 minutes, perform a performance check. Refer to Testing and Adjusting, UENR4125, "Air Conditioning Performance - Test".

System Condition 12

• Water is in the vents.

• Water is leaking from the unit.

Probable Cause

• The non-return valve of the drain.

1. Check the non-return valve for proper positioning and proper direction.

The Compressor will not Engage

If the machine is equipped with the refrigerant compressor protection system, refer to the Testing and Adjusting, UENR4125, "Compressor Protection System - Test" to test the refrigerant compressor on delay timer assembly.

System Condition 13

1. Low-pressure gauge reading is above normal. For normal operating pressures, refer to Table 1.

2. High-pressure gauge reading is below normal. For normal operating pressures, refer to Table 1.

   Note: Ambient temperature is above 21°C (70°F).

3. Air flow to the operator compartment is warm.

Probable Cause

1. The evaporator sensor is stuck open. This condition does not allow the magnetic clutch to cycle the compressor.

   1. Check the wire connectors on the evaporator sensor and the magnetic clutch.

2. The connection of the wire leads on the sensor is improper. The connection of wire leads on the magnetic clutch is improper.

   1. Check for insulation that is broken. The insulation failure can expose the wires from the sensor to the magnetic clutch.

3. The wire that connects the sensor to the magnetic clutch has an opening.

   1. Check the resistance of the coil with a multimeter. Refer to the Testing and Adjusting, UENR4125, "Refrigerant Compressor - Test" section.

   2. Check for the proper electrical ground at the magnetic clutch.

   3. Touch the two wires on the sensor together. Check for the proper operation of the magnetic clutch.

   4. To check the electrical components, refer to Testing and Adjusting, UENR4125, "Machine Preparation For Testing and Adjusting".

      If the problem is a loose wire on the sensor or a loose wire on the magnetic clutch, make the repairs that are needed. If the wires to the clutch are damaged, the damaged wires can cause the sensor to remain open. Make the needed repairs to the damaged wires. To ensure the correct system operation, complete a performance check. Testing and Adjusting, UENR4125, "Air Conditioning Performance - Test".

The Compressor Continues to Cycle or the Clutch will not Disengage.

Note: The cause of the problem may be one of the following conditions: low charge, overcharge, and evaporator freeze-up.

System Condition 14

1. Low-pressure gauge reading is below normal. For normal operating pressures, refer to Table 1.

2. High-pressure gauge reading is below normal. For normal operating pressures, refer to Table 1.

   Note: Ambient temperature is above 21°C (70°F).

3. The air flow to the operator compartment is cold, or the air flow may be restricted completely at times.

Probable Cause

The thermostat switch is held closed. There is a short in the wire to the magnetic clutch. The magnetic clutch will not release.

• Check the wire that goes to the magnetic clutch. The wire may have an electrical short.

• Make the necessary repairs to the magnetic clutch.

Additional Refrigerant Circuit Problems for Orifice Tube System

System Condition 15

The compressor clutch is engaged but the system has insufficient cooling.

Probable Cause

• The system is improperly charged.

• Restrictions, insects, foreign material in the condenser, or any restriction of air flow can cause insufficient cooling.

• A restriction in a liquid line or a low amount of refrigerant charge can cause insufficient cooling.

1. Install the manifold gauge set. Refer to the Testing and Adjusting, UENR4125, "Manifold Gauge Set (Refrigerant) - Install" section.

2. Start the engine. Operate the engine at 1400 rpm. Move the temperature control knob to the Maximum position and the fan to the High position. Close all windows and doors. To stabilize the system, operate the system for a minimum of 10 minutes.

   Note: Ambient temperature is above 21°C (70°F).

3. The outlet on the accumulator should be cold to the touch. If the outlet is not cold, check the readings on the manifold gauges.

   • If the low side reading is above 345 kPa (50 psi), check for a missing orifice tube. Refer to Disassembly and Assembly, UENR4125, "Orifice Tube (Air Conditioner) - Remove and Install".

   • If the low side reading is into vacuum, check for a plugged orifice tube or a restriction in the line.

   • A restriction in the liquid line can be detected by running a hand along the line until there is a change in temperature. A change in temperature in the line will usually indicate the location of the restriction.

4. If the inlet and the outlet on the accumulator are warm, refer to the Testing and Adjusting, UENR4125, "Refrigerant System - Charge" section in Testing and Adjusting. Also, refer to the Testing and Adjusting, UENR4125, "Refrigerant Leakage-Test" section in Testing and Adjusting.

False Seizure of the Compressor

On the initial start-up of the air conditioner system, slipping and broken drive belts may be experienced if the air conditioner system has not been used for an extended period. Also, scored clutch surfaces may be experienced. Scoring would indicate a seized compressor. However, replacement of the compressor may not be necessary.

Changes in temperature can cause expansion of the refrigerant in the compressor during extended periods of non-use. Also, changes in temperature can cause contraction of the refrigerant in the compressor during extended periods of non-use. During this movement, lubricating oil that is carried by the refrigerant migrates. The lubricating oil moves away from highly polished surfaces in the compressor. Without lubricating oil at the polished surfaces, the polished surfaces rub together, appearing as a seized compressor.

The compressor should be checked for seizure before the compressor is replaced. Use the procedures that follow to check the compressor for seizure.

1. With a spanner wrench on the clutch drive plate, rock the shaft in the opposite direction of normal rotation.

2. After the clutch drive plate is movable, rotate the clutch drive plate at least three complete revolutions in the counterclockwise direction.

3. Start the engine. Operate the compressor for a minimum of 1 minute.

   This procedure will not correct a seized compressor. However, this procedure should be attempted before you replace a compressor that has been idle for a month or longer.