Diagnosis By Refrigerant Pressure: Notes

WARNING: This page is about a different car, the 2014 Mitsubishi Outlander. However, it is still accessible from the selected car via links, so may be relevant.

A/C system symptom	Measurement circumstance				Cause	Measures
A/C system symptom	High pressure	Low pressure	Air outlet temperature	Note	Cause	Measures
Cooler is not effective.	Low	High	High	Pressure for low pressure side is high, and high pressure side is low. When the A/C operation is stopped, the pressures of low pressure side and high pressure side immediately become identical.	Leakage inside compressor Faulty compression of compressor	Check according to the compressor check. When no foreign object is present to the oil, and when the color is light grey, replace only the compressor. When foreign objects are mixed to the oil, and the color is black, replace the compressor and receiver. Perform the evacuation sufficiently to remove the foreign objects and moisture in the cycle. Fill the new gas to the specified amount.
Cooler is not effective.	High	High	High	Low pressure side/high pressure side pressure is too high. Low pressure side piping is too hot to touch.	Air is mixed to the refrigerant cycle. Evacuation is insufficient.	Perform the evacuation sufficiently, and remove the foreign objects and moisture in the cycle. Fill the new gas to the specified amount.
Sufficient cooling and insufficient cooling occur periodically.	Fluctuation	Fluctuation	Fluctuation	During the air conditioning operation, the low pressure side pressure alternates between the negative pressure and normal. (also in the high pressure side, the abnormal and normal statuses are alternated).	The moisture in the refrigerant cycle becomes frozen in the expansion valve, then the circulation of refrigerant is stopped temporarily. Subsequently, the status recovers to normal by the melting of ice.	Replace the receiver (drier). Perform the evacuation sufficiently, and remove the moisture in the cycle. Fill the new refrigerant to the specified amount.
Cooler is sometimes not effective. (works occasionally)	Low	Vacuum	Fluctuation	The low pressure side pressure indicates the vacuum, and the high pressure side indicates the low pressure. To the piping before and after the expansion valve, frost or dew is observed.	The foreign objects or moisture inside the refrigerant cycle deposits or freezes inside the expansion valve, and the refrigerant flow is disturbed. Because of the expansion valve operation failure, the refrigerant flow is disturbed.	Check the expansion valve. If foreign objects are present inside the expansion valve, remove them by using an air gun or others. When no foreign object is present, the expansion valve operation failure is suspected. Therefore, replace the expansion valve. Perform the evacuation sufficiently, and remove the foreign objects and moisture in the cycle. Fill the new refrigerant to the specified amount.
Cooling effectiveness is bad.	Low	Low	Slightly high	Low pressure side/high pressure side pressure is low. Outlet air temperature is high.	Gas leakage is present to somewhere in the refrigerant cycle. Refrigerant gas amount is insufficient.	When the pressure gauge indication is close to zero, check the leak position, and then repair the leakage. Also, when the value is lower than the standard pressure, check if the gas leakage is present, and repair if necessary. After checking the leak position, sufficiently perform the evacuation, then fill the new gas to the specified amount.
	High	High	Slightly high	Low pressure side/high pressure side pressure is too high.	Refrigerant amount is excessive. Condenser cooling is insufficient.	Clean the condenser fin (fouling, fin clogging) Check the condenser fan motor (radiator fan) operation. When 1 and 2 are normal, recover all the refrigerant. Then, perform a sufficient evacuation again, and fill the new gas to the specified amount.
	High	High	High	Low pressure side/high pressure side pressure is too high. Frost or dew is formed to the low pressure side.	Expansion valve trouble (valve opened excessively)	Replace the expansion valve.
	Normal	Normal	Slightly high	-	Because of the slight difference of measurement environment, secular change of vehicle, or others, it is possible that the outlet temperature fluctuation has occurred.	Check the status for a while, and if the status does not improve, recover all the refrigerant, then fill to the appropriate amount.