313D Electrical Components and Wiring 3

Question 1

What does a high-pressure switch do in the electrical circuit of a residential air conditioner?

Accepted Answer

Opens the control circuit if refrigerant pressure exceeds a safe limit

Answer

A high-pressure switch is a normally closed safety device that opens the control circuit—de-energizing the compressor—when discharge pressure exceeds a preset limit.

Question 2

Which NEC article primarily governs the installation of air-conditioning and refrigerating equipment?

Accepted Answer

Article 440

Answer

NEC Article 440 specifically addresses air-conditioning and refrigerating equipment, including motor-compressor branch circuit sizing and protection requirements.

Question 3

A technician finds that a condenser fan motor runs but the compressor does not start and hums loudly. The MOST likely electrical cause is:

Accepted Answer

Open run capacitor for the compressor

Answer

A failed run capacitor reduces starting torque, causing the compressor to hum and fail to start while still drawing locked-rotor amperage.

Question 4

What is the function of the crankcase heater in an air conditioning system, and how is it typically wired?

Accepted Answer

Keeps oil warm to prevent refrigerant migration; wired to be energized when the compressor is OFF

Answer

A crankcase heater prevents liquid refrigerant from migrating into compressor oil during off cycles; it is wired so it energizes whenever the compressor contactor is open.

Question 5

When measuring voltage across a closed contactor's load-side terminals, a technician reads 5V instead of 0V. This most likely indicates:

Accepted Answer

Pitted or burned contacts causing excessive resistance

Answer

A voltage drop across a closed contactor indicates high contact resistance from pitting or burning, which causes heat and inefficient power delivery to the compressor.

(313D) Residential Air Conditioning Systems Mechanic Certification Practice Test

(313D) Residential Air Conditioning Systems Mechanic Certification Practice Test

313D Electrical Components and Wiring 3