Condensate drain traps must be used on draw through evaporator coils in order to prevent:

• A. High air resistance
• B. Water overflow
• C. Drainpipe freezing
• D. Low static pressure

Answer: (B)

When a draw-through evaporator coil operates, the blower creates negative pressure in the drain line as condensate is drained away. Without a trap, this suction can pull condensate back toward the coil, potentially causing the evaporator pan to overflow or water to back up into the air stream. A condensate drain trap provides a small water seal that blocks that backflow, ensuring the condensate continues to drain away properly and preventing overflow in the coil area.

This function isn’t primarily about reducing air resistance, preventing drainpipe freezing, or altering static pressure, which are addressed by other design and operating measures.