7B
A/C System Performance Inspection
1) Conduct the A/C system performance inspection under the following conditions:
• No under direct sun
• No wind or no air circulation by other air conditioner
• Ambient temperature within 25 – 35 °C (77 – 95 °F)
• Relative humidity within 30 – 70%
2) Make sure that high pressure valve (1) and low pressure valve (2) of manifold gauge set (3) are firmly closed.
3) Connect high pressure charging hose (4) to high pressure service valve (5), and connect low pressure charging hose (6) to low pressure service valve (7).
4) Bleed the air in charging hoses (4), (6) by loosening their respective nuts on manifold gauge set (3), utilizing the refrigerant pressure. When a hissing sound is heard, immediately tighten nut.
CAUTION:
Do not interchange high and low pressure charging hoses by mistake.
5) Warm up engine to normal operating temperature (engine coolant temperature at 80 – 90 °C (176 – 194 °F)) and keep it at specified idle speed. (Radiator cooling fan should not be working when checking pressure and temperature.)
6) Turn A/C switch ON, and set blower switch at “HI” (4th position), temperature knob at “COOL”, air outlet control knob at “FACE” and fresh/circulation control knob at “CIRCULATION”. (Confirm that A/C compressor and radiator/condenser cooling fan are working.) Keep all windows, doors and engine food open.
Performance diagnosis condition
Ambient temperature 25 – 35 °C (77 – 95 °F)
Engine rpm At specified idle speed
Blower fan motor switch “H” (4th position)
Temperature control “Cool”
Air outlet control “Face”
Vehicle doors All open
Air inlet door position Recirculation
7) Place dry bulb thermometer (1) to contact center duct air outlet and a wet and dry bulb thermometer (2) near evaporator air inlet, read temperatures and confirm that both temperature and humidity are within the specified condition.
8) Check if each pressure on low side and on high side is within shaded range of the graph.
If each gauge reading is out of specified pressure, correct defective part referring to the following table.
NOTE:
Pressure registered on gauge varies with ambient temperature. Therefore, use the graph when determining if pressures are normal or not.
Low side and high side pressure example for M13 engine model
Gauges should read as follows when ambient temperature is 30 °C (86 °F).
Pressure on high pressure gauge 1480 – 1820 kPa
14.8 – 18.2 kg/cm²
210.5 – 259.0 psi
Pressure on low pressure gauge 290 – 390 kPa
2.9 – 3.9 kg/cm²
41.5 – 55.5 psi
Low side and high side pressure example for K9K engine model
Gauges should read as follows when ambient temperature is 30 °C (86 °F).
Pressure on high pressure gauge 1400 – 1750 kPa
14.0 – 17.5 kg/cm²
199.1 – 248.9 psi
Pressure on low pressure gauge 230 – 350 kPa
2.3 – 3.5 kg/cm²
32.7 – 49.8 psi
9) Check inlet port temperature-to-outlet port temperature relationship using the graph.
For example, if evaporator inlet port temperature is 30 °C (86 °F) and center duct air outlet temperature is 20 °C (68 °F), their crossing point is within acceptable range as shown in the graph.
If crossing point is out of acceptable range, diagnose trouble referring to the following table.
M13 engine model
K9K engine model
High pressure gauge
Condition Possible cause Correction
Pressure is higher than acceptable range
(“A” area) 		Refrigerant overcharged Recharge.
Expansion valve frozen or clogged Check expansion valve.
Clogged refrigerant passage of high side Clean or replace.
Condenser cooling fan malfunction (Insufficient cooling of condenser) Check condenser cooling fan.
Dirty or bent condenser fins (Insufficient cooling of condenser) Clean or repair.
Compressor malfunction (Insufficient oil etc.) Check compressor.
Engine overheat Check engine cooling system referring to Engine Cooling System Inspection and Cleaning:M13A or Engine Cooling System Inspection and Cleaning:K9K .
Pressure is lower than acceptable range
(“B” area) 		Insufficient refrigerant (Insufficient charge or leakage) Check for leakage, repair if necessary and recharge.
Expansion valve malfunction (valve opens too wide) Check expansion valve.
Compressor malfunction (Insufficient compression) Check compressor.
Low pressure gauge
Condition Possible cause Correction
Pressure is higher than acceptable range
(“C” area) 		Expansion valve malfunction (valve opens too wide) Check expansion valve.
Compressor malfunction (Insufficient compression) Check compressor.
Pressure is lower than acceptable range
(“D” area) 		Insufficient refrigerant (Insufficient charge or leakage) Check for leakage, repair if necessary and recharge.
Expansion valve malfunction (valve opens too narrow) Check expansion valve.
Clogged refrigerant passage (crashed pipe) Repair or replace.
Thermometer at center duct
Condition Possible cause Correction
Crossing point is higher than acceptable range (“E” area) Insufficient or excessive charge of refrigerant Check refrigerant pressure.
Dirty or bent A/C evaporator fins Clean or repair.
Air leakage from cooling (heater) unit or air duct Repair or replace.
Malfunctioning, switch over function of door in cooling (heater) unit Repair or replace.
Compressor malfunction Check compressor.
Crossing point is lower than acceptable range (“F” area) Insufficient air volume from center duct (Heater blower malfunction) Check blower motor and fan.
Compressor malfunction Check compressor.
NOTE:
• If ambient temperature is approximately 30 °C (86 °F), it is possible to diagnose A/C system in detail referring to the following table.
• The upper values without asterisk (*) are for M13 engine model.
• The lower values with asterisk (*) are for K9K engine model.
Condition Possible cause Correction
Manifold gauge MPa (kg/cm²) (psi) Detail
Lo Hi
0.29 – 0.39
(2.9 – 3.9)
(42 – 56)
0.27 – 0.37*
(2.7 – 3.7)*
(39 – 53)* 		1.48 – 1.82
(14.8 – 18.2)
(211 – 259)
1.48 – 1.80*
(14.8 – 18.0)*
(211 – 256)* 		Normal condition — —
Negative pressure 0.5 – 0.6
(5 – 6)
(71.2 – 85.3) 		The low pressure side reads a negative pressure, and the high pressure side reads an extremely low pressure.
Presence of frost around tubing to and from receiver/dryer and expansion valve. 		Dust particles or water droplets are either stuck or frozen inside expansion valve, preventing the refrigerant from flowing. Clean expansion valve.
Replace it if it cannot be cleaned.
Replace receiver/dryer.
Evacuate the A/C system and recharge with fresh refrigerant.
Normal:
0.29 – 0.39
(2.9 – 3.9)
(42 – 56)
0.27 – 0.37*
(2.7 – 3.7)*
(39 – 53)*
↑ ↓
Abnormal:
Negative pressure 		Normal:
1.48 – 1.82
(14.8 – 18.2)
(211 – 259)
1.48 – 1.80*
(14.8 – 18.0)*
(211 – 256)*
↑ ↓
Abnormal:
0.69 – 0.98
(7 – 10)
(100 – 142) 		During A/C operation, the low pressure side sometimes indicates negative pressure, and sometimes normal pressure. Also high pressure side reading fluctuates between the abnormal and normal pressure. Expansion valve is frozen due to moisture in the system, and temporarily shuts off the refrigeration cycle. Replace expansion valve.
Replace receiver/dryer.
Evacuate A/C system and recharge with fresh refrigerant.
0.05 – 0.15
(0.5 – 1.5)
(4.2 – 21.3) 		0.69 – 0.98
(7 – 10)
(100 – 142) 		Both low and high pressure sides indicate low readings.
Continuous air bubbles are visible through sight glass.
Output air is slightly cold. 		Insufficient refrigerant in system
(Refrigerant leaking). 		Using leak detector, check for leaks and repair as necessary.
Recharge refrigerant to a specified amount.
If the pressure reading is almost 0 when the manifold gauges are attached, check for any leaks, repair them, and evacuate the system.
0.4 – 0.6
(4 – 6)
(56.9 – 85.3) 		Pressure on low pressure side is high.
Pressure on high pressure side is low.
Both pressure becoming equal right after A/C is turned OFF. 		Internal leak in compressor. Inspect compressor and repair or replace as necessary.
0.35 – 0.45
(3.5 – 4.5)
(50 – 64) 		1.96 – 2.45
(20 – 25)
(285 – 355) 		Pressure on both low and high pressure sides is high.
Air bubbles are not visible even when engine RPM is lowered. 		Overcharged A/C system. Adjust refrigerant to specified amount.
Faulty condenser cooling operation. Clean condenser.
Faulty condenser cooling fan operation. Inspect and repair condenser cooling fan.
Pressure on both low and high pressure sides is high.
Low pressure side tubing is not cold when touched.
Air bubbles are visible through sight glass. 		Presence of air in A/C system
(Improperly evacuated). 		Replace receiver/dryer.
Inspect quantity of compressor oil and presence of contaminants in oil.
Evacuate system and recharge with fresh refrigerant.
0.45 – 0.55
(4.5 – 5.5)
(64 – 78) 		Pressure on both low and high pressure sides is high.
Large amount of frost or dew on the low pressure side tubing. 		Faulty expansion valve.
Refrigerant flow is not regulated properly. 		Replace expansion valve.