Servicing Thermostatic Expansion Valves

Thermostatic Expansion Valves Explained

TEV valves are simply devices which control the rate of flow of refrigerant into the evaporator coil. They achieve this by forcing the high pressure liquid through a small orifice where it exits at a lower pressure into the evaporator coil. To regulate the size of the opening the valve has a temperature bulb connected by a length of copper wire to the valve body. When mounted on the exit side of the evaporator coil the bulb picks up the temperature of the gas and transmits it conductively back to the valve. In this way the rate of high pressure gas flowing into the evaporator coil matches the rate of evaporation.

Troubleshooting and Symptoms

While fixing a broken or malfunctioning TEV valve is going to be beyond the skill and capability of most homeowners to fix. However if you feel that your HVAC system is not producing the cold air like it once did, there are a few things that you can look out for which could point to a malfunctioning TEV valve.

Frosting on the exit side of the evaporator coil, in combination with a noisy compressor can be a sign of flooding. Flooding occurs when the TEV is letting in more refrigerant to the evaporator coil than what can be evaporated off. Flooding can be extremely bad for a compressor as it tries to compress and incompressible liquid.

On the opposite end of TEV problems is starving. When this happens the TEV is not letting enough refrigerant into the evaporator to replace the rate at which it is evaporated off. Most modern HVAC systems will have a low pressure cutoff and run in an equalization mode. However, if you notice your compressor being sluggish and your AC not cooling like it should it can be a sign of starving.

The last malfunction of the TEV is hunting. Hunting is when the TEV will vacillate between starving and flooding, giving you a range of symptoms.

Servicing your TEV

TEV’s are an essential and integral part of your HVAC system. Ensuring their proper function and treating any malfunctions is something that should be handled by trained professionals like we here at ACS Air Conditioning Systems. If your HVAC system isn’t performing like it once did, give us a call and schedule a service call to look over your system.