Rick's Free Auto Repair Advice

AC low side pressure is too high

AC low side pressure is too high — How to check

If you’ve attached gauges to your car’s AC system and the

AC manifold gauge

Manifold gauge set with hoses

pressure readings are steady but the AC low side pressure too high, here are the possibilities:

Possibility #1 AC low side pressure is too high because the system is overcharged

If you’ve recently added refrigerant to the system and are now seeing high low side pressure and warm air coming out of the vents, you may have added too much refrigerant. Evacuate the system and recharge with the exact amount of refrigerant based on the car maker’s specifications.

One way to check for an overcharged condition is to spray water over the condenser fins while the system is running. If low side pressure drop significantly, that’s an indication of an overcharged system.

Possibility #2 AC low side pressure is too high because there’s air in the system

An AC system is a closed system. If you’re low on refrigerant it’s because you have a leak. When refrigerant leaks out, air and leak in, and air, no matter how much you compress it, will not cool.

One way to check for air in the system is to watch the high-pressure reading. Run the system for about 5-mins and shut it off. If the high side pressure drops from around 150-200 to around 28-psi quickly and then falls gradually after that, you’ve got air in the system.

Possibility #3 AC low side pressure is too high because the condenser has reduced airflow

Clogged condenser fins or an inoperative condenser fan can cause low side pressure to be too high. Clean condenser fins and make sure the condenser fan is running at the proper speed.

©, 2020 Rick Muscoplat

Posted on by Rick Muscoplat



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