Rick's Free Auto Repair Advice

Car AC is charged, not cold

Car AC is charged, not cold

If your car AC is charged but not cold, here are the items to check

Did you add refrigerant from a DIY kit?

If your AC is charged but not cold, read this. Over time, most car AC systems develop leaks and lose a small AC Proamount of refrigerant. This happens most often in the winter when the seals and tubes contract. Then, when summer arrives and the tubes and seals expand, it’s hard to find the leak. Most DIYers think they can just top off their car AC system with no downside. WRONG!

Any time an AC system leaks refrigerant out, it also lets outside air in. Air in a car AC system decreases the system’s cooling ability because it takes up space in the condenser, yet it doesn’t condense. So it reduces the condensing capacity of the condenser. To test for air in the system, compare the static pressures listed in this charge to actual readings based on gauges and ambient temperature. See this post for static pressures at ambient temperatures.

Air in the system causes pressures on the high side to be higher than normal and causes the gauge needle to flutter.

But the decrease in cooling is even worse if the air carried in MOISTURE. Refrigerant and refrigerant oil readily absorb moisture when exposed to air. The receiver/drier and accumulator have a bag of desiccant drying agent to remove and hold the moisture, but it has a limited capacity. Over time, the bag of desiccant can fail, spreading the desiccant throughout the system where it clogs the orifice tube and expansion valve.

Worse yet, moisture in the system in concentrations greater than 20ppm can cause serious damage. A single drop of water is enough to push the entire system over the 20-ppm threshold. Water in an AC system reacts with the refrigerant to form hydrochloric acid (HCI). HCI corrodes steel, iron, copper and aluminum. As the metals oxidize, they release particles that combine with the refrigerant oil to form sludge. It’s that sludge that clogs the intake screens to the orifice tubes and expansion valves, preventing them from metering refrigerant into or out of the evaporator.

AC orifice tube

New and clogged AC orifice tube. Clogged tube shows evidence of “Black Death.”

If you frequently add refrigerant from a DIY recharge kit and have finally reached the point where the system is fully charged but not cold, chances are you’ve caused the damage yourself. At this point, the only fix is to open the system, flush the lines, replace the orifice tube/expansion valve, receiver/drier or accumulator, condenser and pull a vacuum for at least 45 minutes to pull all moisture from the system.

What are the symptoms of moisture in the system?

Car AC cools, then blows warm air

What’s happening? Moisture in the system is freezing at the metering valve and restricting the flow of refrigerant.

High condenser pressure is a sign of air in the system.

What to replace?


orifice tube

Orifice tubes are color coded. Buy the same color if you replace yours.

H-block style expansion valve

H-block style expansion valve

+accumulator, receiver dryer

©, 2018 Rick Muscoplat

Posted on by Rick Muscoplat

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