The solenoid valve certainly doesn't top the list of AC components that homeowners are familiar with. However, understanding the basics of your solenoid valve may give you key insights into when your air conditioner is underperforming. Here's an introduction to your central AC solenoid valve. 

What Is a Solenoid Valve?

As its name suggests, a solenoid valve is a valve that relies on a solenoid to control the flow of fluid. A solenoid consists of a cylindrical coil of wire encircling a metal post called an armature. When the solenoid coil is charged, it creates a magnetic field that lifts the armature and opens the attached valve. A spring inside the solenoid valve returns the armature and valve to the closed position when the coil is no longer powered.

Where Is the Solenoid Valve in Your Central AC?

In a central air conditioner, the solenoid valve controls the flow of refrigerant to the evaporator coils. The valve is installed in the main AC refrigerant loop, near the evaporator coils inside your furnace assembly. The solenoid valve works in conjunction with a device called the thermostatic expansion valve, or TE valve. These valves release depressurized refrigerant into the evaporator coils to absorb heat and cool your home's air.

What Are the Signs of AC Solenoid Valve Problems?

When your central AC solenoid valve malfunctions, it causes problems for the entire system. The valve may get stuck in the open position when dirt or corrosion in the valve stem keeps it from closing completely. In other cases, a worn valve seat may prevent the valve from sealing tightly.

An open solenoid valve allows refrigerant to leak into the evaporator coils, which gradually increases pressure inside the AC refrigerant loop. The compressor must run periodically to normalize coolant pressure, wasting energy and shortening the compressor's life.

A solenoid valve can also get stuck in the closed position. This most commonly occurs when power to the solenoid is interrupted or the solenoid coil is burnt out. When the solenoid valve is stuck shut, your AC will be unable to cool and your system will circulate warm air. The valve will need to be replaced to restore refrigerant flow through your air conditioner.

Repairing air conditioners with damaged solenoid valves is a common task for HVAC technicians, but it's beyond the scope of DIY repair. Call a local AC repair contractor if you suspect that a bad solenoid valve may be responsible for your AC problems.