For 1990-2009 cars

## TXV Air Conditioning (A/C) System Diagnosis Insufficient Cooling

### General Information

Certain conditions which are normal to proper air conditioning system operation may lead an owner to wrongly suspect a problem.

The air that discharges from the air conditioning system may not feel as cold as expected under conditions of high humidity. The reason is that the vaporized moisture in humid air heats more effectively than dry air does, making the humid air harder to cool.

In terms of overall comfort, however, the dryer dehumidified air coming from the air conditioning system during hot, humid weather evaporates more moisture on a person's skin, providing more of a cooling effect than might be felt from cooler but more humid air.

This fact should be explained to an owner if no mechanical cause is found for a persistent complaint of insufficient cooling.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 |

1. Turn the ignition switch to LOCK.
2. Test for an open A/C fuse with a J 34764-A . Replace the fuse if necessary.
3. Set the parking brake.
4. Start the engine.
5. Set the blower speed selector switch to any speed except OFF.
6. Press the A/C switch to ON.
7. Turn the blower speed to OFF.
8. Turn the ignition switch to LOCK.
9. Test the A/C fuse with the J 34764-A one more time.

Is the A/C fuse open again?

--

Go to Step 19

Go to Step 2

2 |

1. Turn the ignition switch to ON.
2. Turn the blower speed to the following positions in the following order:

2.1. | OFF

2.2. | LOW

2.3. | MEDIUM 1

2.4. | MEDIUM 2

2.5. | HIGH

2.6. | OFF

3. Turn the ignition switch to LOCK.

Does the blower motor speed increase at each speed level when the blower speed selector is turned towards HIGH and decrease when the blower speed selector switch is turned towards LOW?

--

Go to Step 3

Go to Step 20

3 | Inspect the temperature door operation by turning the temperature control lever quickly from COLD to HOT and back to COLD. Do you hear the temperature door slamming at each end? | -- | Go to Step 4 | Go to Step 21
4 | Inspect for a loose, damaged or missing compressor drive belt. Repair or replace the belt if necessary. Refer to Drive Belt Replacement in Engine Mechanical. Is the inspection complete? | -- | Go to Step 5 | --
5 | Inspect the engine coolant fan operation. Repair if necessary. Is the inspection complete? | -- | Go to Step 6 | --
6 | Inspect the condenser for restricted air flow. Clean or repair as necessary. Is the inspection complete? | -- | Go to Step 7 | --
7 |

1. Verify that the ambient air temperature is at least 16°C (60°F) before continuing to the nest step.
2. Start the engine.
3. Set the air mode to VENT.
4. Set the blower speed to HIGH.
5. Set the temperature control to full COLD.
6. Press the A/C switch to ON.

Does the compressor clutch engage?

--

Go to Step 8

Go to Step 10

8 |

1. Monitor the compressor closely for unusual knocking, loud moaning noises and compressor drive belt slipping.
2. Cycle the compressor clutch by pressing the A/C switch to OFF and back to ON. Verify any noise.
3. Determine if the compressor drive belt is slipping.

Is there excessive compressor noise?

--

Go to Step 22

Go to Step 9

9 | Feel the liquid line between the condenser and the receiver/dryer. The line should feel warm to the touch. Does the line feel cold? | -- | Go to Step 23 | Go to Step 13
10 |

1. Turn the ignition switch to LOCK.
2. Obtain a properly calibrated J 39183-C R-134a manifold gauge set.
3. Connect the LOW and HIGH side pressure gauges to the service ports on the vehicle.
4. Test the system LOW and HIGH side pressures. Both pressures should be almost equal to each other.

Are both LOW and HIGH pressures the same as or higher than the specified value?

345 kPa (50 psi)

Go to Step 24

Go to Step 11

11 | Monitor and compare the LOW and HIGH side pressure readings. Are the LOW and HIGH side pressures within the specified ranges? | 69-345 kPa (10-50 psi) | Go to Step 23 | Go to Step 12
12 |

1. Add 0.45 kg (1 lb) of refrigerant.
2. Inspect the system for refrigerant leaks. Refer to Leak Testing .

Do any refrigerant leaks exist?

--

Go to Step 25

Go to Step 27

13 | Feel the evaporator inlet pipe (the small pipe) and the evaporator outlet pipe at the bulkhead. The evaporator inlet pipe should feel warm to the touch. Does the inlet evaporator feel colder than the evaporator pipe? | -- | Go to Step 14 | Go to Step 17
14 | Inspect the system for refrigerant leaks. Refer to Leak Testing . Does a refrigerant leak exist? | -- | Go to Step 25 | Go to Step 15
15 |

1. Add 0.45 kg (1 lb) of refrigerant.
2. Monitor the compressor clutch cycle rate.

Does the compressor clutch cycle at more than 8 cycles per minute?

--

Go to Step 26

Go to Step 16

16 |

1. Start the engine.
2. Set the air mode control lever to VENT.
3. Set the blower speed selector switch to HIGH.
4. Set the temperature control lever all the way to COLD.
5. Press the A/C switch to ON.
6. Feel the evaporator inlet pipe (the small pipe) and the evaporator outlet pipe at the bulkhead again. The evaporator inlet pipe should feel warm to the touch.

Does the evaporator inlet pipe feel colder than the evaporator outlet pipe?

--

Go to Step 26

Go to Step 27

17 | Test the HIGH pressure. Does the compressor engage within the specified ranges? | 196-3140 kPa (28-455 psi) | Go to Step 18 | Go to Step 28
18 | Run the compressor and monitor both the clutch operation and the HIGH pressure for 5 minutes. Does the compressor stay engaged when the HIGH pressure is outside of the specified ranges? | 196-3140 kPa (28-455 psi) | Go to Step 28 | Go to Step 29
19 | Refer to the applicable procedure for the electrical diagnosis of the compressor magnetic clutch.

• | HVAC Compressor Clutch Does Not Engage

• | HVAC Compressor Clutch Does Not Disengage

Is the action complete?

--

Go to Step 2

--

20 | Refer to the appropriate procedure for the diagnosis of the blower motor.

• | Blower Motor Inoperative at Any Speed

• | Blower Motor Low Speed Inoperative

• | Blower Motor Inoperative Med-1

• | Blower Motor Inoperative Med-2

• | Blower Motor Operates at High Speed Only

• | Blower Motor High Speed Inoperative

• | Blower Motor Always On

Is the action complete?

--

Go to Step 3

--

21 | Refer to the Temperature Control Cable Adjustment . Is the action complete? | -- | Go to Step 4 | --
22 | Refer to Noise Diagnosis and determine the cause of the excessive compressor noise. | -- | Go to Step 9 | --
23 | Repair the restriction in the HIGH side of the refrigerant system. Visually inspect for a line/pipe frost spot in order to locate the restriction. Is the action complete? | -- | Go to Step 13 | --
24 | Refer to the applicable procedure for the electrical diagnosis of the compressor magnetic clutch.

• | HVAC Compressor Clutch Does Not Engage

• | HVAC Compressor Clutch Does Not Disengage

Is the action complete?

--

Go to Step 8

--

25 | Repair the refrigerant leak. Refer to Leak Testing . Is the action complete? | -- | Go to Step 29 | --
26 |

1. Discharge the system.
2. Inspect for a plugged expansion valve or a restriction in the HIGH side of the system. Refer to Thermal Expansion Valve Replacement .

Is the action complete?

--

Go to Step 29

--

27 | Discharge and recharge the system. Refer to Refrigerant Recovery and Recharging . Is the action complete? | -- | Go to Step 29 | --
28 | Replace the A/C refrigerant pressure switch. Refer to Pressure Cycling Switch Replacement . Is the action complete? | -- | Go to Step 29 | --
29 | Perform the A/C performance test. Refer to System Performance Test . Is the action complete? | -- | Go to HVAC System Check | --

## TXV Air Conditioning (A/C) System Diagnosis Reference Table

Symptom | Cause | Correction
--- | --- | ---
High Side Pressure Above Specifications | The refrigerant is overcharged. | Discharge and recharge the refrigeration system. Refer to Refrigerant Recovery and Recharging .
The expansion valve is frozen or clogged. |

1. Remove and inspect the expansion valve.
2. Clean the expansion valve.
3. If the expansion valve is already clean, replace the expansion valve. Refer to Thermal Expansion Valve Replacement .

The is a restriction in the high side . | Inspect the high side hoses/pipes for a restriction. Repair as necessary.
The condenser fan is malfunctioning. | Refer to Condenser Fan Inoperative .
The condenser fins are dirty or bent. | Clean or repair the condenser as necessary. Refer to Condenser Replacement .
The compressor is malfunctioning. | Test the compressor and repair as necessary. Refer to Air Conditioning Compressor Replacement .
The engine is overheating. | Refer to Engine Overheating in Engine Cooling.
High Side Pressure Below Specifications | There is insufficient refrigerant or leakage. | Leak test the system and recharge. Refer to Leak Testing and Refrigerant Recovery and Recharging .
The expansion valve opens too wide. | Refer to Thermal Expansion Valve Replacement .
The compressor is malfunctioning. | Test the compressor and repair as necessary. Refer to Air Conditioning Compressor Replacement .
Low Side Pressure Above Specifications | The expansion valve opens too wide. | Refer to Thermal Expansion Valve Replacement .
The heat sensing tube of the expansion valve is mounted improperly. | Inspect the heat sensing tube location and repair as necessary. Refer to Thermal Expansion Valve Replacement .
The compressor is malfunctioning. | Test the compressor and repair as necessary. Refer to Air Conditioning Compressor Replacement .
Low Side Pressure Below Specifications | There is insufficient refrigerant or leakage. | Leak test the system and recharge. Refer to Leak Testing and Refrigerant Recovery and Recharging .
The expansion valve does not open wide enough. | Refer to Thermal Expansion Valve Replacement .
There is a hose/pipe restriction. | Inspect the hoses/pipes for a restriction. Repair as necessary.
Center Outlet Air Temperature Above Specifications | The refrigerant system is improperly charged. | Discharge and recharge the refrigeration system. Refer to Refrigerant Recovery and Recharging .
The evaporator fins are dirty or bent. | Clean or repair the evaporator as necessary. Refer to Air Conditioning Evaporator Core Replacement .
There is air leakage in the air distribution system. | Refer to HVAC System Check .
The temperature control door is malfunctioning. | Refer to Temperature Control Cable Replacement .
The compressor is malfunctioning. | Test the compressor and repair as necessary. Refer to Air Conditioning Compressor Replacement .
Center Outlet Air Temperature Below Specifications | There is insufficient air volume (blower malfunction). | Refer to HVAC System Check .
The evaporator temperature sensor is malfunctioning. | Refer to HVAC System Check .