What Is An AC Expansion Valve – And How Can A Problem With The Part Hurt Your System?

Your central air conditioner relies on a chemical refrigerant that moves through the system, passes through two different sets of coils for phase changes, and provides the cooling source needed for your indoor air. The refrigerant's trip through the exterior condenser coils turns the gas into a warm liquid, which passes through a lineset into the air handler within your home. The refrigerant eventually heads for evaporator coils for a cooling phase change back into a gas. But first the refrigerant has to pass through the expansion valve.

What is the expansion valve, how can problems with the part hurt your HVAC system, and how can an air conditioning repair company help?

Expansion Valve Definition

The expansion valve controls how much refrigerant can enter the evaporator coils how quickly. The refrigerant needs to enter the evaporator at the right temperature and rate so that the coils can properly perform a phase change to make the refrigerant a gas. The phase change causes the coils to be cold, cools your circulating air, and provides you with a comfortable living environment.

The valve also makes sure the liquid refrigerant doesn't try to flow backwards towards the condensing unit. Liquid refrigerant going back into the condensing unit's compressor can potentially break the compressor and lead to costly repairs.

Problem: Lack of Refrigerant in Coils

If the expansion valve gets stuck shut, the supply of refrigerant entering the evaporator coils will be minimal or nonexistent. The lack of refrigerant means the coils have no chemicals to change and thus will not become cool. No cooled coils means the circulating air passing across the coils and out of your vents is going to be as warm as the air was when it entered the system.

Has your system suddenly stopped putting out cold air? Check to make sure the coils aren't frozen, which indicates the coils are receiving refrigerant but a slightly low supply that needs topping off from an HVAC tech. If the coils look fine and the fan is operating, call at tech to check on the expansion valve.

Problem: Allowing Refrigerant to Backwash

If the coils do experience a problem such as freezing or a break that causes a refrigerant leak, the phase change can fail to happen and send the liquid refrigerant backwards towards the supply lines. If the expansion valve isn't working to prevent this backwash, the liquid refrigerant can continue down the refrigerant supply coils. The liquid will then go into the condenser coils, which aren't designed to change the liquid back to a gas, and then end up inside the compressor, which is also not designed to do anything with a liquid refrigerant.

The backflow of refrigerant can lead to extensive and expensive damage inside your condensing unit. And the only real sign that the problem is starting to happen is ice on your refrigerant supply lines. If you spot the ice, turn off the power to your air conditioner immediately and call an HVAC company like Pristine Air Conditioning Corp for a service call.