On-Vehicle Inspection

HINT:

This is a method where a manifold gauge set is used to help locate the problem.

1. Read the manifold gauge pressure when the following conditions are established.

   Test conditions:

   • Temperature at the air inlet with the switch set at RECIRC is 30 to 35°C (86 to 95°F).
   • Engine is running at 1500 rpm.
   • Blower speed control switch is at "HI".
   • Temperature control dial is at "COOL".
   • A/C switch is ON.
   • Doors are fully open.
   1. Normally functioning refrigeration system

      Gauge Reading 

      REFRIGERATION VOLUME AND PRESSURE REFERENCE
      
      

      Pressure Side	Refrigerant Volume
      Low	0.15 to 0.25 MPa (1.5 to 2.5 kgf/cm2 , 21 to 36 psi)
      High	1.37 to 1.57 MPa (13.9 to 16.0 kgf/cm2 , 198 to 227 psi)

   2. Moisture is present in refrigeration system.
      Fig 1: Checking A/C Refrigeration Pressure

      Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      Fig 2: Checking A/C Refrigeration Pressure For Moisture Is Present In Refrigeration System

      Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      PROBLEM SYMPTOM CHART
      
      

      Symptom	Probable Cause	Diagnosis	Corrective Action
      During operation, pressure on low pressure side cycles between normal and vacuum	Moisture in the A/C system will freeze at the expansion valve orifice, causing the refrigeration cycle to temporarily stop After the system stops, and warms up again, the ice will melt and normal operation will be temporarily restored	Cooler dryer (integrated into the condenser tank) in over saturated state Moisture in the refrigeration system freezes at the expansion valve orifice and blocks circulation of refrigerant	Replace the cooler dryer Remove moisture in the system by repeatedly evacuating air Supply a proper amount of new refrigerant

   3. Insufficient cooling
      Fig 3: Checking A/C Refrigerant Pressure For Insufficient Cooling

      Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      PROBLEM SYMPTOM CHART
      
      

      Symptom	Probable Cause	Diagnosis	Corrective Action
      Pressure is low on both low and high pressure sides Insufficient cooling performance	Gas leakage from the refrigeration system	Insufficient refrigerant Refrigerant leaking	Check for gas leaks and repair if necessary Supply a proper amount of new refrigerant If the gauge indicates a pressure of close to 0, then it will be necessary to evacuate the system after repairing the leak

   4. Poor circulation of refrigerant
      Fig 4: Checking A/C Refrigerant Pressure For Poor Circulation Of Refrigerant

      Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      PROBLEM SYMPTOM CHART
      
      

      Symptom	Probable Cause	Diagnosis	Corrective Action
      Pressure is low on both low and high pressure sides Frost exists on pipe from condenser to unit	Refrigerant flow is obstructed by dirt inside the pipes of the condenser core	Receiver is clogged	Replace the condenser

   5. Refrigerant does not circulate.
      Fig 5: Checking A/C Refrigerant Pressure For Refrigerant Does Not Circulate

      Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      PROBLEM SYMPTOM CHART
      
      

      Symptom	Probable Cause	Diagnosis	Corrective Action
      Vacuum is indicated on low pressure side and very low pressure is indicated on high pressure side Frost or condensation is seen on piping on both sides of receiver/drier or expansion valve	Refrigerant flow is obstructed by moisture or dirt in the refrigeration system Refrigerant flow is obstructed by gas leaking internally through the expansion valve	Refrigerant does not circulate	Check the expansion valve Replace the expansion valve Replace the condenser Evacuate air and supply a proper amount of new refrigerant For internal gas leak at the expansion valve, replace the expansion valve

   6. Refrigerant is overcharged or cooling effectiveness of the condenser is insufficient.
      Fig 6: Checking A/C Refrigerant Pressure For Refrigerant Overcharged

      Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      PROBLEM SYMPTOM CHART
      
      

      Symptom	Probable Cause	Diagnosis	Corrective Action
      Pressure is too high on both low and high pressure sides	Unable to develop sufficient performance due to an excessive use of refrigeration system Cooling effectiveness of the condenser is insufficient	Excessive refrigerant in cycle → excessive refrigerant was added during recharging Condenser cooling effectiveness is insufficient → condenser fins are clogged at the cooling fan	Clean the condenser Check the operation of the condenser cooling fan If 1 and 2 are normal state, check the amount of refrigerant and supply the proper amount of refrigerant

   7. Air is present in the refrigeration system.
      Fig 7: Checking A/C Refrigerant Pressure For Air Present In Refrigeration System

      Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      PROBLEM SYMPTOM CHART
      
      

      Symptom	Probable Cause	Diagnosis	Corrective Action
      Pressure is too high on both low and high pressure sides The low pressure piping is too hot to touch	Air in the system	Air present in the refrigeration system Insufficient vacuum purging	Check compressor oil to see if it is dirty or insufficient Evacuate the system and recharge it with new or purified refrigerant

   8. Expansion valve malfunction
      Fig 8: Checking A/C Refrigerant Pressure For Expansion Valve Malfunction

      Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      PROBLEM SYMPTOM CHART
      
      

      Symptom	Probable Cause	Diagnosis	Corrective Action
      Pressure is too high on both low and high pressure sides Frost or a large amount of condensation on piping on low pressure side	Expansion valve may be sticking	Excessive refrigerant in low pressure piping Expansion valve opened too wide	Check expansion valve

   9. Insufficient compressor compression
   Fig 9: Checking A/C Refrigerant Pressure For Insufficient Compressor Compression

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
   PROBLEM SYMPTOM CHART
   
   

   Symptom	Probable Cause	Diagnosis	Corrective Action
   Pressure is too high both on low and high pressure sides Pressure is too low on high pressure side	Internal leak in the compressor	Low compression Leak from a damaged valve, or parts may be broken	Replace the compressor

   Gauge readings (Reference)

   Fig 10: A/C Refrigerant Pressure Graph

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002