Air Conditioning Refrigerant Expansion Valve

Meters refrigerant into the evaporator. It is the restriction that drops high-pressure liquid to low pressure, and that pressure drop is what makes the evaporator cold in the first place — so how far it opens sets how much cooling the system can produce.

It is not the refrigerant distribution valve, and confusing the two sends a diagnosis to the wrong end of the system. A distribution valve decides which evaporator gets refrigerant on a vehicle that has more than one; an expansion valve decides how much gets through, and every air conditioning system has one whether or not it has a second evaporator.

On most cars it is purely mechanical and has no wiring at all — a thermostatic valve with a sensing bulb on the evaporator outlet, opening and closing itself. Only an electronically actuated one can set a fault code, and those are fitted where the circuit has to do more than cool a cabin: heat pumps that run it backwards for heating, and electric vehicles that chill the traction battery through the same refrigerant.

Its characteristic failure is mechanical rather than electrical. A stepper that loses steps, a valve stiffened by debris or migrated compressor oil, or a drifted position all produce cooling that is weak rather than absent, and a low-side pressure that will not settle where it should. A system genuinely low on refrigerant cools badly everywhere and consistently — which is the distinction worth making before anyone books a regas.

Also known as: expansion valve, electronic expansion valve, EXV, ac expansion valve, thermal expansion valve, TXV

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