Gauge indication
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Refrigerant cycle
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Probable cause
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Corrective action
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Both high‐ and low‐pressure sides are too high.

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The pressure returns to normal is reduced soon after water is splashed on condenser.
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Excessive refrigerant charge in refrigeration cycle.
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Reduce refrigerant until specified pressure is obtained.
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Air suction by cooling fan is insufficient.
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Insufficient condenser cooling performance. ↓
- Condenser fins are clogged.
- Improper fan rotation of cooling fan.
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- Clean condenser.
- Check and repair cooling fan if necessary.
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- 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.
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Poor heat exchange in condenser (After compressor operation stops, high-pressure decreases too slowly). ↓ Air in refrigeration cycle.
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Evacuate repeatedly and recharge system.
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Engine tends to overheat.
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Engine cooling systems malfunction.
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Check and repair each engine cooling system.
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- An area of the low‐pressure pipe is colder than areas near the evaporator outlet.
- Low‐pressure pipe is sometimes covered with frost.
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- 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.
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Replace expansion valve.
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High‐pressure side is too high and low‐pressure side is too low.

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Upper side of condenser and high‐pressure side are hot, however, liquid tank is not so hot.
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High‐pressure tube or parts located between compressor and condenser are clogged or crushed.
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- Check and repair or replace malfunctioning parts.
- Check lubricant for contamination.
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High‐pressure side is too low and low‐pressure side is too high.

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

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- 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.
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Liquid tank inside is slightly clogged.
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- Replace liquid tank.
- Check lubricant for contamination.
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- 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.
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High‐pressure pipe located between liquid tank and expansion valve is clogged.
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- Check and repair malfunctioning parts.
- Check lubricant for contamination.
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Expansion valve and liquid tank are warm or slightly cool when touched.
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Low refrigerant charge. ↓ Leaking fittings or components.
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Check refrigerant for leakages. Refer to Refrigerant Leakages.
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There is a big temperature difference between expansion valve inlet and outlet while the valve itself is frosted.
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Expansion valve closes a little compared with the specification. ↓
- Improper expansion valve adjustment.
- Malfunctioning expansion valve.
- Outlet and inlet may be clogged.
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- Remove foreign particles by using compressed air.
- Replace expansion valve.
- Check lubricant for contamination.
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An area of the low‐pressure pipe is colder than areas near the evaporator outlet.
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Low‐pressure pipe is clogged or crushed.
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- Check and repair malfunctioning parts.
- Check lubricant for contamination.
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Air flow volume is not enough or is too low.
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Evaporator is frozen.
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Low‐pressure side sometimes becomes negative.

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- 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.
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Refrigerant does not discharge cyclically. ↓ Moisture is frozen at expansion valve outlet and inlet. ↓ Water is mixed with refrigerant.
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- Drain water from refrigerant or replace refrigerant.
- Replace liquid tank.
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Low‐pressure side becomes negative.

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Liquid tank or front/rear side of expansion valve’s pipe is frosted or wet with dew.
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High‐pressure side is closed and refrigerant does not flow. ↓ Expansion valve or liquid tank is frosted.
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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.
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