Which fault is most likely to cause high suction pressure and high discharge pressure in an air conditioning system?

• A. A dirty evaporator
• B. A TEV bulb detached from the suction line
• C. A faulty condenser fan motor
• D. A low refrigerant charge

Answer: (C)

When pressures on both sides of the system rise, the problem is often in heat rejection. The condenser is where hot refrigerant is cooled and condensed back into a liquid, and the condenser fan moves air across those coils to remove that heat. If the condenser fan motor isn’t working, heat isn’t rejected effectively, so the condenser temperature and pressure climb. The compressor now has to work against this higher head pressure, which pushes discharge pressure up and tends to raise suction pressure as the system responds to the overall higher pressures. So a faulty condenser fan motor directly explains simultaneous high suction and high discharge pressures.

Other faults don’t typically produce this combination as reliably. A dirty evaporator mainly restricts heat absorption and can reduce suction pressure rather than raise it. A detached TEV bulb disrupts refrigerant metering and can cause unstable or improper pressures, but it doesn’t as clearly tie to elevated both sides. A low refrigerant charge reduces available refrigerant and usually lowers both pressures rather than raising them.