A/C Employment Ready Certification Practice Test

When a TEV (Thermal Expansion Valve) sensing bulb becomes detached from the suction line, it affects the functioning of the valve. The sensing bulb is responsible for detecting the temperature of the refrigerant in the suction line, which in turn influences the amount of refrigerant that flows into the evaporator.

If the bulb is detached, it cannot accurately sense the temperature of the suction line. This leads to improper modulation of refrigerant flow. Typically, if the bulb detects high temperatures, it opens the valve more to allow additional refrigerant flow; if it detects low temperatures, it closes the valve. Upon detachment, the bulb often "thinks" the temperature is lower than it is, or it does not register any temperature at all. Consequently, the valve may stay in a position that allows excessive refrigerant into the evaporator, leading to higher suction pressure since the evaporator is flooded with more refrigerant than it can efficiently boil off.

At the same time, this increased flow of refrigerant into the evaporator can cause an accumulation of refrigerant at the compressor, resulting in a higher than normal discharge pressure as well. Therefore, the outcome of a detached TEV sensing bulb is characterized by high suction pressure and higher than normal discharge