A OF a TEV bulb that has detached from the suction line will typically produce which pressure condition?

• 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: (B)

When the sensing bulb of a thermostatic expansion valve is in proper contact with the suction line, it reads the evaporator temperature and adjusts flow to maintain stable superheat. If the bulb becomes detached, it no longer senses the suction-line temperature accurately and sits at ambient temperature. Ambient is generally higher than the evaporator temperature, so the bulb pressure rises relative to what the valve should see. That higher sensed pressure makes the valve think the evaporator is hotter than it really is, causing it to restrict flow to the evaporator. With less refrigerant entering the evaporator, the evaporator vaporizes less, pulling the suction pressure down. The compressor then handles a lighter load, so the discharge pressure also drops. Hence, the detachment typically results in low suction pressure and low discharge pressure.