When troubleshooting an air conditioning system, the operating pressures are 40 psig on the low side and 116 psig on the high side. What is the most likely problem?

• A. Refrigerant leak
• B. Low refrigerant charge
• C. Compressor failure
• D. Blocked or closed valve

Answer: (D)

When an air conditioning system is running, the compressor moves refrigerant from the low-pressure side (evaporator) to the high-pressure side (condenser). If the high-side path is blocked or a valve on that path is closed, refrigerant can’t leave the compressor into the condenser. The suction side keeps drawing refrigerant, so the low-side pressure stays around the expected level (about 40 psi here), but the high side backs up and climbs (about 116 psi). That pattern—normal-ish low-side pressure with elevated high-side pressure—points to a restriction or closed valve on the high-pressure path.

refrigerant leaks or low refrigerant charge would generally cause low readings on both sides, and compressor failure often disrupts both sides or removes compression rather than simply raising the high-side pressure due to a downstream blockage.