How to identify a malfunctioning expansion valve

How To Identify A Malfunctioning Expansion Valve?

An expansion valve is that part of the mobile A/C system that controls the amount of refrigerant flowing into the system to cool the interior of the car. When you turn the warm/cool knob on the A/C slot, the expansion valve is the part that gets the signal and acts accordingly. The expansion valve is what acts as the divider between the high pressure and low pressure segments of the A/C unit.

How Does An Expansion Valve Malfunction?

There is a brass tube with a very small hole that lets the refrigerant liquid pass from the high pressure segment to the low pressure segment. Since this hole is extremely small, it needs to be able to allow the high pressure to low pressure cooling take place. There are screens on either sides of this hole. That is the only filter this hole gets. In a factory installed car, there is no other protection for this little passage.

Debris from other parts of the entire A/C system flows into these screens and blocks them. This eventually renders the orifice tube incapable to meter the required amount of refrigerant flow into the evaporator. Hence, this little part of the A/C system is enough to make the entire system malfunction, when not serviced in time.

Symptoms Of An Malfunctioning Expansion Valve

The cause of the problem is understood. Now, let’s find out how would we know that the problem has occurred. In other words, how do you know that an A/C system issue is caused by a malfunctioning expansion valve?

The first sign of an expansion valve malfunction is proper cooling in the beginning, but performance starts to lag after a few minutes. When the problem is only starting to occur, the expansion valve still manages to function when the A/C is turned on. However, after some time, that little hole does not receive enough refrigerant. When your car AC system cools the interior when turned on, but then starts warming it up instead, know that the orifice tube needs servicing.

A manifold gauge might also give erratic pressure readings. This is another giveaway. The low pressure side readings will be abnormally low. But this has got nothing to do with lowered amount of refrigerant, but the blocked passage in the orifice tube instead. Confirm the problem by taking the higher pressure side readings. It will be too high.

Get your car A/C system serviced immediately when any of these symptoms arise.