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Refrigeration & Air Conditioning Mechanic Red Seal · Question

A residential split-system air conditioner is experiencing recurring coil icing on the evaporator. The outdoor temperature is moderate (18°C / 64°F). What is the most probable cause requiring attention beyond simple defrosting?

A restricted liquid line filter drier reduces the amount of refrigerant flowing to the evaporator coil. This leads to a significant drop in evaporator pressure

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Question: A residential split-system air conditioner is experiencing recurring coil icing on the evaporator. The outdoor temperature is moderate (18°C / 64°F). What is the most probable cause requiring attention beyond simple defrosting?

Answer options:

  • Excessive refrigerant charge ✅ A restricted liquid line filter drier
  • An oversized condenser unit
  • Leaky return air ductwork in an unconditioned attic

Correct answer: A restricted liquid line filter drier

Explanation: A restricted liquid line filter drier reduces the amount of refrigerant flowing to the evaporator coil. This leads to a significant drop in evaporator pressure and temperature, causing the coil to operate below freezing point and ice up, even in moderate ambient conditions.

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