Pressure Test

PRESSURE TEST CHART

Test results	Related symptoms	Probable cause	Remedy
Suction and discharge pressures are normal	Warm air from the vents.	The A/C system contains too much refrigerant oil The air mix door is not operating properly	Recover refrigerant (see REFRIGERANT RECOVERY ), and evacuate the system (see SYSTEM EVACUATION ). Adjust the amount of oil in the system, then recharge the system (see SYSTEM CHARGING ). Check air mix door operation (see AIR MIX CONTROL MOTOR TEST ), and repair as needed.
Suction and discharge pressures are roughly equal and steady	The suction and discharge pressures equalize when the engine is revved.	The A/C compressor clutch or the drive belt is slipping, or the compressor shaft seal is leaking	Check whether the A/C compressor clutch or the drive belt is slipping. If the drive belt is slipping, replace the drive belt (see DRIVE BELT INSPECTION ). If the A/C compressor clutch is slipping, replace it (see A/C COMPRESSOR CLUTCH OVERHAUL ). Check the A/C compressor shaft seal. If it's leaking, replace the A/C compressor (see A/C COMPRESSOR REPLACEMENT ).
Suction and discharge pressures are roughly equal but fluctuate	Suction and discharge pressures fluctuate while running. Pressures equalize as soon as the A/C compressor disengages.	The compressor discharge valve or the compressor gasket is faulty	Replace the A/C compressor (see A/C COMPRESSOR REPLACEMENT ).
Suction and discharge pressures are roughly equal and abnormally low	The suction and discharge pressures do not change during continued operation.	The A/C system is undercharged	Recover refrigerant (see REFRIGERANT RECOVERY ), then do the refrigerant leak check (see REFRIGERANT LEAK CHECK ). Repair any leaks, then recharge the system (see SYSTEM CHARGING ).
Suction and discharge pressures are abnormally high, but normalize when the condenser is cooled	The suction pressure decreases when cool water is sprayed on the A/C condenser.	The A/C system is overcharged	Recover refrigerant (see REFRIGERANT RECOVERY ), evacuate the system (see SYSTEM EVACUATION ), and recharge the system to specifications (see SYSTEM CHARGING ).
Suction and discharge pressures are abnormally high, and refrigerant line temperatures are abnormal	The high pressure vapor line to the condenser is too hot. The low pressure liquid line from the expansion valve is not cold. There is an abrupt temperature drop along a refrigerant line, or in the condenser or evaporator.	The A/C system refrigerant flow is restricted	Replace the restricted line or component.
Suction and discharge pressures are abnormally high, but drop rapidly when the compressor disengages	After stopping the A/C compressor, the discharge pressure quickly drops about 196 kPa (28 psi), then falls gradually. The input and output temperatures at the expansion valve are not similar.	There is excess air in the A/ C system	Recover refrigerant (see REFRIGERANT RECOVERY ), evacuate the system (see SYSTEM EVACUATION ), and recharge the system (see SYSTEM CHARGING ).
Suction and discharge pressures are abnormally high, and there is little or no airflow through the A/C condenser		The condenser and/or radiator fins are clogged The condenser fins are damaged The condenser and/or radiator fans are not working properly	Clean debris from the condenser and/or radiator fins. Comb the condenser fins to repair any damage. Troubleshoot the A/C condenser fan and/or the radiator fan circuit(s).
The suction pressure is high and the discharge pressure is low. Both pressures are steady	The liquid line temperature is similar on both sides of expansion valve. System pressures do not vary at a steady engine speed.	The expansion valve is stuck open	Replace the expansion valve (see EXPANSION VALVE REPLACEMENT ).
The suction pressure is low, the discharge pressure is high, and the refrigerant temperature changes abnormally somewhere in the system	The high pressure liquid line going into the expansion valve is cold. There is an abrupt temperature drop in the line between the compressor and the condenser, or in the line between the condenser and the expansion valve.	The A/C system refrigerant flow is restricted	Replace the restricted line or component.
The suction pressure is high, the discharge pressure is low, and there are particle contaminants in the refrigerant lines	The expansion valve and/or the compressor discharge hose are contaminated with metal flakes or desiccant particles.	The A/C compressor is malfunctioning	Replace the A/C compressor (see A/C COMPRESSOR REPLACEMENT ). If the system is contaminated with desiccant, replace the receiver/dryer (see A/C LINE REPLACEMENT ).
The suction pressure is high, the discharge pressure is low, and the pressures quickly change when the A/C disengages	The discharge and suction pressures equalize soon after the A/C compressor stops.	The A/C compressor seal is faulty	Replace the A/C compressor (see A/C COMPRESSOR REPLACEMENT ).
Suction and discharge pressures are both low and none of the refrigerant lines are cold	There is no frost on the expansion valve, and the low-pressure liquid line is not cold.	The A/C system has a leak (very low refrigerant charge)	Do the refrigerant leak check (see REFRIGERANT LEAK CHECK ), repair any leaks, and recharge the A/C system (see SYSTEM CHARGING ).
Suction and discharge pressures are both low, and the expansion valve or the suction line is abnormally cold	The temperature around the expansion valve is too low compared to the temperature around the receiver/dryer. The low pressure (suction) hose/line is cooler than the evaporator.	The discharge hose/line is clogged or kinked, which is restricting refrigerant flow The suction hose/line is clogged or kinked, which is restricting refrigerant flow	Repair or replace the faulty A/C line (see A/C LINE REPLACEMENT ).
Initially, the suction and discharge pressure are normal, but both become abnormally low during operation	During extended operation, the air flow from the vents decreases.	The evaporator is freezing up	Run the fan with A/C compressor off to warm the evaporator, then test the evaporator temperature sensor (see EVAPORATOR TEMPERATURE SENSOR TEST ). If necessary, replace the evaporator temperature sensor.
Suction and discharge pressures are both low and there are abnormal temperature changes at the expansion valve	During extended operation, warm air comes out of the vents, the suction pressure decreases, and heavy frost occurs on the low pressure liquid line. The low pressure liquid line is cold at the expansion valve, but warm after the valve. There is frost on the expansion valve.	The expansion valve is stuck closed	Replace the expansion valve (see EXPANSION VALVE REPLACEMENT ), and the receiver/dryer (see A/C LINE REPLACEMENT ). Check the old expansion valve for contamination. If contaminants are found, replace the component that caused the contamination.
The discharge pressure is low, the suction pressure is extremely low, and the expansion valve outlet is abnormally warm	There is no frost on the expansion valve outlet, and the liquid line temperature changes significantly across the expansion valve.	There is excessive moisture in the A/C system	Recover refrigerant (see REFRIGERANT RECOVERY ), then replace the receiver/dryer (see A/C LINE REPLACEMENT ). Evacuate the system (see SYSTEM EVACUATION ), and recharge the A/C system (see SYSTEM CHARGING ).
The discharge pressure is low, the suction pressure is extremely low, and the suction line is abnormally cold	There is frost on the line from the evaporator to the compressor.	The evaporator is internally contaminated or plugged	Recover refrigerant (see REFRIGERANT RECOVERY ), then replace the evaporator. Evacuate the system (see SYSTEM EVACUATION ), and recharge the A/C system (see SYSTEM CHARGING ).
The discharge pressure is low, the suction pressure is extremely low, and the refrigerant temperature doesn't change going through the expansion valve	There is no frost on the expansion valve, and the low pressure liquid line is not cold. The liquid line temperatures are similar on both sides of expansion valve.	The expansion valve is faulty	Replace the expansion valve (see EXPANSION VALVE REPLACEMENT ).
The discharge pressure is low, the suction pressure is extremely low, and the expansion valve is abnormally cold	There is frost on the expansion valve.	Excessive moisture in the system is freezing the expansion valve	Recover refrigerant (see REFRIGERANT RECOVERY ), the replace the receiver/dryer. Evacuate the system (see SYSTEM EVACUATION ), and recharge the system (see SYSTEM CHARGING ).
The discharge pressure is low, the suction pressure is extremely low, and the high pressure liquid line is abnormally cold	There is frost on the line from the receiver/dryer to the expansion valve.	The receiver/dryer is clogged	Recover refrigerant (see REFRIGERANT RECOVERY ), then replace the receiver/dryer. Evacuate the system (see SYSTEM EVACUATION ), and recharge the A/C system (see SYSTEM CHARGING ).