313D Electrical Systems and Controls 4

Question 1

A residential thermostat's R terminal is energized and the Y terminal is calling for cooling, but the contactor does not pull in. Voltage measured at the contactor coil terminals is 0V. The MOST likely cause is:

Accepted Answer

An open safety switch or broken wire in the Y control circuit

Answer

Zero volts at the coil means the 24V signal never reached the contactor, pointing to an open in the control circuit such as a tripped safety switch.

Question 2

Which NEC article covers 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 circuit requirements.

Question 3

What does the minimum circuit ampacity (MCA) rating on an AC unit nameplate tell the installer?

Accepted Answer

The minimum wire size required to safely supply the unit

Answer

MCA specifies the minimum ampacity the supply conductors must have, ensuring wiring can handle continuous operation without overheating.

Question 4

A residential outdoor unit has a maximum overcurrent protection (MOCP) rating of 35A on its nameplate. The installer should use a breaker that is:

Accepted Answer

35A or less

Answer

The MOCP is the maximum allowable breaker size; you may use any standard size up to and including 35A.

Question 5

Which tool is used to verify that a 240V circuit is correctly wired with both hot legs and a ground, without a neutral?

Accepted Answer

Non-contact voltage tester on each leg and a multimeter leg-to-leg and leg-to-ground

Answer

You confirm 240V leg-to-leg and ~120V from each hot leg to ground using a multimeter; a non-contact tester confirms both conductors are energized.

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

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

313D Electrical Systems and Controls 4