After stopping the compressor, the pressure drops about 299 kPa (28 psi) quickly, then falls gradually

There is air in the system.

Recover, evacuate, and recharge the system with the specified amount of refrigerant.

The condenser is excessively hot.

There is excessive refrigerant in the system.

Recover, evacuate, and recharge the system with the specified amount of refrigerant.

Reduced or no airflow through the condenser.

The condenser or the radiator fins are clogged.

Clean the condenser or the radiator fins.

The condenser or the radiator fan is not working properly.

The line to the condenser is excessively hot.

Restricted flow of refrigerant in the system.

Locate and repair the restriction.

The condenser is not hot.

Insufficient refrigerant in the system

High and low pressures are balanced soon after stopping the compressor.

Low-side pressure is higher than normal.

Faulty compressor pressure relief valve

Repair or replace the compressor.

Faulty compressor seal

The outlet of the expansion valve is not frosted, low pressure gage indicates vacuum

Faulty expansion valve

Replace the expansion valve.

Moisture in the system

Recover, evacuate, and recharge the system.

The condenser is not hot.

Insufficient refrigerant in the system

Repair the leaks. Recover, evacuate, and recharge the system.

The expansion valve is not frosted and the low pressure line is not cold.

The low pressure gage indicates a vacuum.

Frozen expansion valve

Replace the expansion valve.

Faulty expansion valve

The discharge temperature is low and the air flow from the vents is restricted.

The evaporator is frozen.

Clear the restricted evaporator case drain.

The expansion valve is frosted.

The expansion valve is clogged.

Clean or replace the expansion valve.

The receiver/drier outlet is cool and the inlet is warm.

The receiver/drier is clogged.

Replace the receiver/drier.

The low pressure hose and check joint are cooler than the temperature around the evaporator.

The expansion valve is opened for too long.

Replace the expansion valve.

A capillary tube is loose.

Suction pressure is lowered when the condenser is cooled by water.

There is excessive refrigerant in the system.

Recover, evacuate, and recharge the system.

High and low pressure are equalized as soon as the compressor is stopped and both gages fluctuate while the compressor is running.

A gasket is faulty.

Repair or replace the compressor.

The high pressure valve is faulty.

Foreign particles are stuck in the high pressure valve.

Reduced airflow through the condenser

The condenser or the radiator fins are clogged.

Clean the condenser and the radiator.

The radiator cooling fans are not working properly.

The condenser is excessively hot.

There is excessive refrigerant in the system.

Recover, evacuate, and recharge the system.

The low pressure hose and metal end areas are cooler than the evaporator.

Clogged or kinked low pressure hose

Repair or replace the low pressure hose.

The temperature around the expansion valve is low compared to that around the receiver/dryer.

The high pressure line is clogged.

Repair or replace the high pressure line.

The compressor clutch is dirty.

The compressor shaft seal is leaking.

Repair or replace the compressor.

The compressor bolts are dirty.

Leaking around a compressor housing bolt.

Tighten the bolt(s) or replace the compressor.

The compressor gasket is wet with oil.

The compressor gasket is leaking.

Repair or replace the compressor.