Gauge indication | Refrigerant cycle | Probable cause | Corrective action
Both high‐ and low‐pressure sides are too high. | The pressure returns to normal is reduced soon after water is splashed on condenser. | Excessive refrigerant charge in refrigeration cycle. | Reduce refrigerant until specified pressure is obtained.
Air suction by cooling fan is insufficient. | Insufficient condenser cooling performance. ↓

1. Condenser fins are clogged.
2. Improper fan rotation of cooling fan.

- Clean condenser.
- Check and repair cooling fan if necessary.

- Low‐pressure pipe is not cold.
- When compressor is stopped, high‐pressure reading quickly drops by approximately 196 kPa (2 kg/cm2, 28 psi). It then decreases gradually thereafter.

Poor heat exchange in condenser
(After compressor operation stops, high-pressure decreases too slowly).
↓
Air in refrigeration cycle.
Evacuate repeatedly and recharge system.
Engine tends to overheat. | Engine cooling systems malfunction. | Check and repair each engine cooling system.

- An area of the low‐pressure pipe is colder than areas near the evaporator outlet.
- Low‐pressure pipe is sometimes covered with frost.

- Excessive liquid refrigerant on low‐pressure side.
- Excessive refrigerant discharge flow.
- Expansion valve is open a little compared with the specification.

↓
Improper expansion valve adjustment.
Replace expansion valve.
High‐pressure side is too high and low‐pressure side is too low. | Upper side of condenser and high‐pressure side are hot, however, liquid tank is not so hot. | High‐pressure tube or parts located between compressor and condenser are clogged or crushed. |

- Check and repair or replace malfunctioning parts.
- Check lubricant for contamination.

High‐pressure side is too low and low‐pressure side is too high. | High‐ and low‐pressure sides become equal soon after compressor operation stops. | Compressor pressure operation is improper. ↓ Damaged inside compressor packings. | Replace compressor.
No temperature difference between high‐ and low‐pressure sides. | Compressor pressure operation is improper. ↓ Damaged inside compressor packings. | Replace compressor.
Both high‐ and low‐pressure sides are too low. |

- There is a big temperature difference between liquid tank outlet and inlet. Outlet temperature is extremely low.
- Liquid tank inlet and expansion valve are frosted.

Liquid tank inside is slightly clogged.

- Replace liquid tank.
- Check lubricant for contamination.

- Expansion valve inlet temperature is extremely low as compared with areas near liquid tank.
- Expansion valve inlet is frosted.
- Temperature difference occurs somewhere in high‐pressure side.

High‐pressure pipe located between liquid tank and expansion valve is clogged.

- Check and repair malfunctioning parts.
- Check lubricant for contamination.

Expansion valve and liquid tank are warm or slightly cool when touched. | Low refrigerant charge. ↓ Leaking fittings or components. | Check refrigerant for leakages. Refer to Refrigerant Leakages.
There is a big temperature difference between expansion valve inlet and outlet while the valve itself is frosted. | Expansion valve closes a little compared with the specification. ↓

1. Improper expansion valve adjustment.
2. Malfunctioning expansion valve.
3. Outlet and inlet may be clogged.

- Remove foreign particles by using compressed air.
- Replace expansion valve.
- Check lubricant for contamination.

An area of the low‐pressure pipe is colder than areas near the evaporator outlet. | Low‐pressure pipe is clogged or crushed. |

- Check and repair malfunctioning parts.
- Check lubricant for contamination.

Air flow volume is not enough or is too low. | Evaporator is frozen. |

- Check intake sensor circuit.
  Refer to Diagnosis Procedure.
- Replace compressor.
- Repair evaporator fins.
- Replace evaporator.
- Check the blower motor circuit. Refer to Diagnosis Procedure.

Low‐pressure side sometimes becomes negative. |

- Air conditioning system does not function and does not cyclically cool the compartment air.
- The system constantly functions for a period of time after compressor is stopped and restarted.

Refrigerant does not discharge cyclically.
↓
Moisture is frozen at expansion valve outlet and inlet.
↓
Water is mixed with refrigerant.

- Drain water from refrigerant or replace refrigerant.
- Replace liquid tank.

Low‐pressure side becomes negative. | Liquid tank or front/rear side of expansion valve’s pipe is frosted or wet with dew. | High‐pressure side is closed and refrigerant does not flow. ↓ Expansion valve or liquid tank is frosted. | Leave the system at rest until no frost is present. Start it again to check whether or not the malfunction is caused by water or foreign particles.

- Cooling is initially okay if water is the cause. Then the water freezes causing a blockage. Drain water from refrigerant or replace refrigerant.
- Remove expansion valve and remove the particles with dry and compressed air (not shop air) if due to foreign particles.
- Replace expansion valve if either of the above methods cannot correct the malfunction.
- Replace liquid tank.
- Check lubricant for contamination.