Which condition is typically observed when a TEV bulb becomes detached from the suction line?

Which condition is typically observed when a TEV bulb becomes detached from the suction line?

• A. High suction pressure and high discharge pressure
• B. Low suction pressure and low discharge pressure
• C. Low suction pressure and high discharge pressure
• D. High suction pressure and lower than normal discharge pressure

Answer: (D)

The sensing bulb on a thermostatic expansion valve provides the pressure signal that trims the valve opening. When the bulb becomes detached from the suction line, that temperature/pressure signal is lost, so the valve can’t modulate properly. Without the bulb’s influence, the valve tends to stay more open than it should, allowing more refrigerant into the evaporator. Fueling the evaporator more than designed increases the evaporating pressure, raising the suction (evaporator) pressure. At the same time, the compressor’s discharge pressure can be lower than normal because the flow dynamics through the system are not being correctly controlled, so the head pressure doesn’t rise as it normally would under proper metering. So, a detached bulb typically presents as higher suction pressure with discharge pressure that is lower than normal, reflecting the loss of proper metering and control of refrigerant flow. If you observe this, check the bulb attachment and the capillary tube for leaks or breaks.

The sensing bulb on a thermostatic expansion valve provides the pressure signal that trims the valve opening. When the bulb becomes detached from the suction line, that temperature/pressure signal is lost, so the valve can’t modulate properly. Without the bulb’s influence, the valve tends to stay more open than it should, allowing more refrigerant into the evaporator.

Fueling the evaporator more than designed increases the evaporating pressure, raising the suction (evaporator) pressure. At the same time, the compressor’s discharge pressure can be lower than normal because the flow dynamics through the system are not being correctly controlled, so the head pressure doesn’t rise as it normally would under proper metering.

So, a detached bulb typically presents as higher suction pressure with discharge pressure that is lower than normal, reflecting the loss of proper metering and control of refrigerant flow. If you observe this, check the bulb attachment and the capillary tube for leaks or breaks.