HVAC System Components & Diagnostics Flashcards

Which motor protection device disconnects a compressor motor when it draws excessive current over a prolonged period?

Answer: Thermal overload relay

A thermal overload relay monitors motor current and trips the contactor to protect the motor winding from overheating due to sustained overcurrent conditions.

A hydronic heating system has poor heat distribution with some zones too hot and others too cold. What procedure corrects this?

Answer: Balancing the system using circuit balancing valves and flow meters

Hydronic system balancing using circuit balancing valves and flow measurement ensures each zone receives its design flow rate for proper heat distribution.

What is the function of a hot gas bypass valve in a refrigeration system?

Answer: Maintains minimum compressor load at reduced system demand to prevent short-cycling

A hot gas bypass valve injects discharge gas into the suction line to create artificial load, preventing compressor short-cycling at low evaporator loads.

When testing for duct leakage using duct pressurization, the technician measures leakage at 25 Pa. What CFM25 result indicates a code-compliant new residential duct system?

Answer: Leakage not exceeding 4 CFM25 per 100 sq ft of conditioned floor area

ASHRAE 90.1 and most energy codes require duct leakage not to exceed 4 CFM25 per 100 square feet of conditioned floor area for new construction.

A refrigeration system uses R-404A. The EPA Section 608 de minimis threshold for this refrigerant is exceeded. What must the technician do?

Answer: Repair the leak within 30 days or reduce charge below threshold

EPA Section 608 requires technicians to repair leaks in systems above the de minimis threshold within 30 days or reduce the charge below the threshold amount.

In a variable refrigerant flow (VRF) system, what is the role of the branch circuit controller (BCC)?

Answer: Distributes refrigerant to multiple indoor units and enables simultaneous heating and cooling

The branch circuit controller in a heat recovery VRF system directs refrigerant to indoor units in either heating or cooling mode, enabling simultaneous operation.

A technician measures 12 inches WC static pressure drop across a dirty air filter where the clean filter drop was 0.5 inches WC. What is the most likely consequence if the filter is not replaced?

Answer: Evaporator coil will freeze due to reduced airflow

A severely restricted filter drastically reduces airflow across the evaporator coil, causing the coil surface temperature to drop below freezing and ice formation.