Auto A/C Terms - Glossary
Low Suction Pressure

Suction pressures refer to the low side pressure gauge readings on an A/C system. When those pressures drop below their expected normal range, they are considered low and the A/C system will require service in order to restore full cooling performance.

Understand that each of the A/C system designs will have different normal or expected low pressures. However, the low pressures should never be so low as to allow the condensation on the evaporator to freeze. Should that happen, air flow over the evaporator is reduced or eliminated and cooling performance is lost.

Low side suction pressures are usually a result of low refrigerant charge or a restriction in the system preventing enough refrigerant to enter the evaporator.

When encountering low suction pressures, the quickest test is to add some refrigerant to the system. If adding refrigerant improves suction pressures, then the system should be leak checked, vacuumed and recharged. If adding some refrigerant does not improve the suction pressures, the system most likely has a restriction at the expansion valve or receiver drier.