The very last thing you want or expect when you turn your heater is for cold air to start venting into your house. In the case of heat pumps, this is an uncommon but frustrating problem. Fortunately, there is a fairly simple solution, though your HVAC technician will need to be the one to implement it. Before we explain what causes this problem, we have to understand how the heat pump switches between modes.
The Reversing Valve
Inside every heat pump is a part called a “reversing valve.” This valve sits at the junction of the central unit exhaust valve, intake valve, and both the indoor and outdoor unit lines. Inside this valve is a slide that controls which direction the refrigerant flows through the system. Depending on the direction, either the indoor or outdoor unit will blow hot air while the other blows cool air. This is what allows the heat pump to change modes.
Attached to the reversing valve is a solenoid, which operates an electro-magnet in the valve itself. The solenoid has two modes: “relaxed” and “energized.” All this really means is whether or not it has an electrical current running through it. When the solenoid is energized it activates an electromagnet which moves the slide from one position to the other and reverses the flow of refrigerant.
Common Problems with the Reversing Valve
Most often, the reason the heat pump gets stuck on one mode or the other is because the solenoid on the reversing valve is bad. If the solenoid is not working properly, it can’t move the slide from one side of the valve to the other. This essentially removes the heat pump’s ability to switch freely between heating and cooling modes.
So how can this be fixed? Often, the first thing an HVAC technician will do is check the solenoid for a magnetic charge. If it is displaying a charge, then something else might be responsible. Often, however, the solution is simply to replace the solenoid.