Rick's Free Auto Repair Advice

Symptoms of a bad expansion valve

What are the symptoms of a bad expansion valve?

Car AC system isn’t cooling enough or won’t cool at all

Whether you have an H-block or remote sensing bulb expansion valve, a loss of gas in the power head can prevent the valve from opening. That results in no cooling. So the air will be noticeably less cold or blow warm.

High side pressure is high

The compressor is compressing refrigerant, sending it to the receiver drier and condenser and the high pressure refrigerant is flowing to the expansion valve. Unfortunately, the valve is closed. So you see very high side pressures. High pressure alone doesn’t mean the expansion valve is bad. High pressure can also be caused by a restriction in the condenser. However, in that case you should get some cooling in the AC vents.

Air coming from vents is frosty

If the expansion valve allows too much refrigerant flow, the evaporator will get so cold that it forms frost or even ice on the fins. Moisture in the cabin air can freeze into ice crystals and blow out the vents.

AC blows cold, then hot

This can be a symptom of a low refrigerant charge. But if you’ve confirmed that the system has the proper charge and it still blows cold and then stops and blows warm air, the metering pin in the expansion valve maybe sticking open or closed.

AC kicks on and then immediately kicks off

This feels almost like and engine miss. Stuck metering pin in expansion valve. What’s happening here is that the compressor is kicking on, refrigerant pressure rises rapidly and the high pressure switch cuts off the AC compressor clutch. This feel almost like an engine miss except that it only happens when you turn on the AC.

Airflow drops dramatically from vents

In this case, the AC comes on strong, blowing very cold air. After a short period you notice the airflow decreasing until the point where very little air is coming from the vents and that air is warm. If you confirm that the system has the correct refrigerant charge, what’s happening is that the expansion valve is allowing too much refrigerant flow which causes the moisture in the air to freeze on the evaporator. This condition would also cause the compressor to run constantly. You’d see a corresponding drop in gas mileage.

©, 2019 Rick Muscoplat

Posted on by Rick Muscoplat

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