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Heavy Duty Equipment Technician Red Seal Exam Prep · Question

An off-highway haul truck's cab pressurization system is functioning, but the operator complains of excessive dust infiltration. The blower motor is operating correctly, and the cabin filter was recently replaced. What is the most likely cause?

Cab pressurization systems operate by maintaining a positive pressure inside the cab to prevent dust and other contaminants from entering. If the blower is func

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Question: An off-highway haul truck's cab pressurization system is functioning, but the operator complains of excessive dust infiltration. The blower motor is operating correctly, and the cabin filter was recently replaced. What is the most likely cause?

Answer options: ✅ A seal around a door or window is compromised.

  • The evaporator core is frozen due to low refrigerant.
  • The condenser is blocked, reducing A/C performance.
  • The HVAC control module has an intermittent fault.

Correct answer: A seal around a door or window is compromised.

Explanation: Cab pressurization systems operate by maintaining a positive pressure inside the cab to prevent dust and other contaminants from entering. If the blower is functioning and the filter is good, dust ingress points to a loss of cab integrity, most commonly a failed or deteriorated door or window seal.

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