System Installation and Startup Flashcards

When installing a variable-speed air handler, which wiring connection is required that is NOT typically needed for single-speed PSC motor units?

Answer: Common (C) wire to power the control board

Variable-speed air handlers require a 24V common (C) wire to power the communicating control board and variable-speed motor module continuously.

A technician installs an auxiliary drain pan under an attic air handler. What additional safety device should be wired into the system to prevent ceiling water damage?

Answer: Auxiliary drain pan float switch wired to interrupt cooling

A float switch in the auxiliary pan is wired to interrupt the cooling circuit so the system shuts down before the secondary pan overflows and damages the ceiling.

Which condition during first startup indicates the system was NOT properly evacuated before charging?

Answer: Operating pressures are unstable and the system has a high moisture reading on the sight glass

Unstable pressures and a moisture indicator changing color on the sight glass confirm non-condensables or moisture were left in the system from inadequate evacuation.

A new installation requires refrigerant line sets running 75 feet. How should the technician adjust refrigerant charge compared to the manufacturer's standard charge?

Answer: Add refrigerant per manufacturer's line-length charging chart for the additional footage

Manufacturers publish line-length charging charts; additional refrigerant must be added beyond the factory charge to account for the extra liquid line volume of longer runs.

During installation, the technician discovers the existing electrical disconnect is rated at 30A but the new unit's MCA is 24A and MOCP is 35A. What is the correct action?

Answer: Use the existing 30A disconnect — it is within the MOCP range

The disconnect must be rated at or above the MCA (24A) and the OCPD must not exceed the MOCP (35A); a 30A rated disconnect satisfies both requirements.

What is the primary reason for insulating the suction line on a new residential AC installation?

Answer: To prevent condensation on the line and maintain superheat to the compressor

Suction line insulation prevents condensation (which causes dripping and potential mold) and reduces heat gain into the cold suction vapor, preserving superheat to protect the compressor.

After completing a residential system installation and commissioning, which parameter should the technician record on the startup documentation for future reference?

Answer: Actual measured suction pressure, discharge pressure, superheat, subcooling, and Delta-T at design conditions

Recording actual operating pressures, superheat, subcooling, and Delta-T at commissioning establishes a baseline for diagnosing future performance changes.