Rick's Free Auto Repair Advice

Abnormal AC manifold gauge readings

What does abnormal AC manifold gauge readings mean?

How to diagnose car AC with manifold gauges

Low side low/high side low: system low on charge

Low side reads 15-30-psi and high side reads 110-150

AC system low on charge

AC manifold gauges show system is low on charge

Low cooling

Low side is low. High side normal to slightly low


Low on refrigerant charge

Restriction in the low side of the system causing evaporator starvation.

Restricted or plugged orifice tube

Problem with expansion valve

Moisture in the system. Moisture collects and freezes on the expansion valve or orifice tube, cutting off flow of refrigerant into evaporator.

To test for moisture: Turn AC off for 10-15 mins, then back on. If gauge reading goes back to low low side reading, the orifice tube or expansion valve screen is likely plugged. If the gauge reading is normal when first turned on and stays normal for a few minutes, you get cold air and THEN low side goes low, that’s a sign of moisture in the system.

Evaporator icing due to starvation. Refrigerant dwells too long in evaporator and picks up superheat causing the evaporator to freeze and restricts airflow. Turn off AC and leave blower on high to melt ice. Once airflow comes back turn AC on. If the cycle repeats, the evaporator is icing up. Caused by low charge, low airflow (plugged cabin air filter), faulty expansion valve sensing bulb or faulty evaporator temp sensor.

In an expansion valve system where the valve is located on the evaporator outlet

Low side VERY low/high side low: restriction

car ac overcharged

bad ac compressorbbbb

Posted on by Rick Muscoplat

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