Trouble Diagnosis for Abnormal Pressure

Petrol Model

NOTE:

Normal pressure for high pressure gauge (HI) and low pressure gauge (LO) in the following table are those measured when the ambient temperature is about 30 °C (86 °F). As normal pressure for both gauges vary depending on the ambient temperature, perform the following steps before starting diagnosis of troubles.

1.Measure the ambient temperature and using that temperature, read the normal high and low pressure from the graph given in Step 9 of A/C System Performance Inspection:Manual Type.
2.Use these values in place of the normal pressure in the following table.

Condition			Possible cause	Correction
Manifold gauge (kPa (kgf/cm²) (psi))		Detail
LO	HI	Detail
HFC-134a model: 250 – 390 (2.5 – 4.0) (36.2 – 56.5) HFO-1234yf model: 230 – 340 (2.3 – 3.5) (33.5 – 49.3)	HFC-134a model: 1400 – 1730 (14.3 – 17.6) (203 – 250) HFO-1234yf model: 1270 – 1630 (13.0 – 16.6) (184 – 236)	Normal condition	—	—
Negative pressure	500 – 600 (5.1 – 6.1) (72.5 – 87.0)	LO gauge reads negative pressure, while HI gauge reads extremely low pressure. Presence of frost around tubing to and from condenser assembly and expansion valve.	Dust particles accumulate or water droplets are frozen inside expansion valve, preventing refrigerant from flowing.	Replace expansion valve. Replace condenser assembly. Evacuate A/C system and recharge system with fresh refrigerant.
HFC-134a model normal condition: 250 – 390 (2.5 – 4.0) (36.2 – 56.5) ↑ ↓ HFC-134a model Abnormal condition: Negative pressure HFO-1234yf model normal condition: 230 – 340 (2.3 – 3.5) (33.5 – 49.3) ↑ ↓ HFO-1234yf model Abnormal condition: Negative pressure	HFC-134a model normal condition: 1400 – 1730 (14.3 – 17.6) (203 – 250) ↑ ↓ HFC-134a model Abnormal condition: 700 – 1000 (7.1 – 10.2) (102 – 145) HFO-1234yf model normal condition: 1270 – 1630 (13.0 – 16.6) (184 – 236) ↑ ↓ HFO-1234yf model Abnormal condition: 700 – 1000 (7.1 – 10.2) (102 – 145)	During A/C operation, LO gauge sometimes indicates negative pressure, and sometimes normal pressure. Also HI gauge reading fluctuates between abnormal and normal pressures.	Expansion valve is frozen due to moisture in system, temporarily shutting off refrigeration cycle.	Replace expansion valve. Replace condenser assembly. Evacuate A/C system and recharge system with fresh refrigerant.
50 – 150 (0.5 – 1.5) (7.25 – 21.8)	700 – 1000 (7.1 – 10.2) (102 – 145)	Both LO and HI gauges indicate low readings. Output air is slightly cold.	Insufficient refrigerant in system (refrigerant leakage).	Using leak detector, check for leakage and repair if necessary. Recharge system with refrigerant to specified amount. If pressure reading is almost 0 when manifold gauges are attached, check for any leakage, repair them, and evacuate system.
400 – 600 (4.1 – 6.1) (58.0 – 87.0)	700 – 1000 (7.1 – 10.2) (102 – 145)	Pressure on LO gauge is high. Pressure on HI gauge is low. Both pressures become equal right after A/C is turned OFF.	Internal leakage in compressor.	Check compressor and repair or replace if necessary.
400 – 450 (4.1 – 4.6) (58.0 – 65.3)	2000 – 2500 (20.4 – 25.5) (290 – 363)	High pressure readings on both LO and HI gauges.	Overcharged A/C system.	Adjust refrigerant to specified amount.
			Faulty radiator cooling operation.	Clean condenser.
			Faulty radiator cooling fan operation.	Check and repair radiator cooling fan.
		High pressure reading on both LO and HI gauges. Low pressure tubing is not cold when touched.	Presence of air in A/C system (improperly evacuated).	Replace condenser. Check quantity of compressor oil and presence of contaminants in oil. Evacuate system and recharge system with fresh refrigerant.
450 – 550 (4.6 – 5.6) (65.3 – 79.8)		High pressure reading on both LO and HI gauges. Large amount of frost or dew on low pressure tubing.	Faulty expansion valve. Refrigerant flow is not regulated properly.	Replace expansion valve.

Diesel Model

NOTE:

Normal pressure for pressure gauge (HI) and low pressure gauge (LO) in the following table are those measured when the ambient temperature is about 30 °C (86 °F). As normal pressure for both gauges vary depending on the ambient temperature, perform the following steps before starting diagnosis of troubles.

Condition			Possible cause	Correction
Manifold gauge (kPa (kgf/cm²) (psi))		Detail
LO	HI	Detail
HFC-134a model: 220 – 300 (2.2 – 3.1) (31.9 – 43.5) HFO-1234fy model 230 – 340 (2.3 – 3.5) (33.3 – 49.3)	HFC-134a model: 1400 – 1870 (14.3 – 19.1) (203 – 271) HFO-1234yf model 1350 – 1870 (13.8 – 19.1) (195 – 271)	Normal condition	—	—
Negative pressure	500 – 600 (5.1 – 6.1) (72.5 – 87.0)	LO gauge reads negative pressure, while HI gauge reads extremely low pressure. Presence of frost around tubing to and from condenser assembly and expansion valve.	Dust particles accumulate or water droplets are frozen inside expansion valve, preventing refrigerant from flowing.	Replace expansion valve. Replace condenser assembly. Evacuate A/C system and recharge system with fresh refrigerant.
HFC-134a model normal condition: 220 – 300 (2.2 – 3.1) (31.9 – 43.5) ↑ ↓ HFC-134a model abnormal condition: Negative pressure HFO-1234yf model normal condition: 230 – 340 (2.3 – 3.5) (33.3 – 49.3) ↑ ↓ HFO-1234yf model abnormal condition: Negative pressure	HFC-134a model normal condition: 1400 – 1870 (14.3 – 19.1) (203 – 271) ↑ ↓ HFC-134a model abnormal condition: Negative pressure HFO-1234yf model normal condition: 1350 – 1870 (13.8 – 19.1) (195 – 271) ↑ ↓ HFO-1234yf model abnormal condition: 700 – 1000 (7.1 – 10.2) (102 – 145)	During A/C operation, LO gauge sometimes indicates negative pressure, and sometimes normal pressure. Also HI gauge reading fluctuates between abnormal and normal pressures.	Expansion valve is frozen due to moisture in system, temporarily shutting off refrigeration cycle.	Replace expansion valve. Replace condenser assembly. Evacuate A/C system and recharge system with fresh refrigerant.
50 – 150 (0.5 – 1.5) (7.25 – 21.8)	700 – 1000 (7.1 – 10.2) (102 – 145)	Both LO and HI gauges indicate low readings. Output air is slightly cold.	Insufficient refrigerant in system (refrigerant leakage).	Using leak detector, check for leakage and repair if necessary. Recharge system with refrigerant to specified amount. If pressure readings are almost 0 when manifold gauges are attached, check for any leakage, repair them, and evacuate system.
400 – 600 (4.1 – 6.1) (58.0 – 87.0)	700 – 1000 (7.1 – 10.2) (102 – 145)	Pressure on LO gauge is high. Pressure on HI gauge is low. Both pressures become equal right after A/C is turned OFF.	Internal leakage in compressor.	Check compressor and repair or replace if necessary.
400 – 450 (4.1 – 4.6) (58.0 – 65.3)	2000 – 2500 (20.4 – 25.5) (290 – 363)	High pressure readings on both LO and HI gauges.	Overcharged A/C system.	Adjust refrigerant to specified amount.
			Faulty radiator cooling operation.	Clean condenser.
			Faulty radiator cooling fan operation.	Check and repair radiator cooling fan.
		High pressure reading on both LO and HI gauges. Low pressure tubing is not cold when touched.	Presence of air in A/C system (improperly evacuated).	Replace condenser. Check quantity of compressor oil and presence of contaminants in oil. Evacuate system and recharge system with fresh refrigerant.
450 – 550 (4.6 – 5.6) (65.3 – 79.8)		High pressure reading on both LO and HI gauges. Large amount of frost or dew on low pressure tubing.	Faulty expansion valve. Refrigerant flow is not regulated properly.	Replace expansion valve.