When your technician says that the problem with your heating and air conditioning system lies with your system’s thermostatic expansion valve (TXV), you might wonder what that actually means. Understanding the importance of the part that broke makes it easier to understand why the technician recommends that you get it fixed immediately.
What Does the Thermostatic Expansion Valve Do?
Your system’s TXV precisely regulates the rate at which liquid refrigerant travels to the evaporator. Your HVAC needs the flow controlled to the evaporator for optimum efficiency and to prevent too much refrigerant from flowing and flooding the system, creating flood-back to the compressor.
The TXV measures the superheat from boiling off the liquid refrigerant. Superheating refers to a rise in gas temperature above the boiling point of a liquid. This must occur since sending too much liquid refrigerant to the compressor damages it. When the TXV reads the heat, it decreases or increases refrigerant flow accordingly to regulate the amount that reaches the evaporator.
Another job of the TXV is the separation of the low- and high-pressure sides of the air conditioner. Liquid refrigerant enters the TXV under high pressure, but the valve stops too much liquid refrigerant from entering the evaporator.
The Misunderstood TXV
The thermostatic expansion valve might be the most misunderstood piece of an HVAC system. Many people confuse its use and think that it controls the system’s:
- Air temperature
- Head pressure
- Suction pressure
You should not try to alter your system to rig the TXV to control any variable besides regulating the rate liquid refrigerant travels to the evaporator. That’s its only job although its job includes three activities. You could cause compressor failure in your system if you do otherwise.
Another frequently misunderstood point is that the TXV only functions as a meter. This isn’t the case. It functions as a meter and a controller. It monitors and controls the flow. Let’s look at how the TXV regulates and does its job.
How the TXV Regulates
The TXV monitors the speed at which the liquid refrigerant boils off in the evaporator coil to maintain the right amount of refrigerant flowing into the evaporator. The TXV does this by responding to a couple of variables – the refrigerant vapor’s temperature as it moves out of the evaporator and the internal evaporator pressure.
The TXV has a multitude of small parts. One of these is the movable valve pin that provides precise control by moving against the spring pressure. It does the job of restricting liquid refrigerant flow. Here’s how that works.
When the valve pin moves against the spring to create pressure, the amount of liquid refrigerant drops. Some of the liquid refrigerant gets converted to a gaseous state. The flash gas occurs because of the high degree of energy transfer. Sensible heat gets converted to latent heat.
This gas vapor and low-pressure liquid combine and move inside the evaporator. While inside the evaporator, the liquid refrigerant boils off, and all of it converts to a gaseous state.
The pressure drop that occurs in the thermostatic expansion valve is critical to the operation of the refrigeration system. As it moves through the evaporator, the low-pressure liquid and gas combination continues to vaporize, absorbing heat from the system load. For the system to operate properly, the TXV must precisely control the flow of liquid refrigerant in response to system conditions.
Signs of a Broken TXV
When you hear your HVAC system making odd noises, such as squealing, squeaking, or rumbling, this signals that the TXV has an issue.
Since the TXV handles such specific activities, it makes it easy for your HVAC technician to determine when it is broken. When they note overflow to the compressor or flood-back to the evaporator, your tech can tell that there is something wrong with the TXV.
You need the thermostatic expansion valve repaired immediately. Your HVAC cannot function properly with it broken. It will either flood or starve your system. Champaign, IL, isn’t a place where you should live without heat.
Call us today if you suspect a bad TXV valve. Bash Heating & Air Conditioning, Inc. services the Champaign-Urbana metro area. You can also set up regular AC maintenance, service, and repair visits at this time to have our company help you keep your HVAC system in top condition. Contact Bash Heating & Air Conditioning, Inc. today to schedule your appointment.