313D Electrical Systems and Controls 2

Question 1

What is the purpose of a time-delay fuse in a residential AC disconnect box?

Accepted Answer

To allow momentary inrush current during compressor startup without blowing

Answer

To slow down the circuit breaker response for safety

Answer

To reduce voltage spikes during normal operation

Answer

To prevent nuisance tripping during brownout conditions

Question 2

A residential condenser fan motor has three leads labeled common, start, and run. Which winding has the highest resistance?

Accepted Answer

Start winding

Answer

Run winding

Answer

Common lead

Answer

Both windings are equal

Question 3

When measuring amperage on a dual-voltage (208/240V) compressor operating at 240V, the current draw is 18A. What would you expect if the same compressor runs at 208V?

Accepted Answer

Higher amperage

Answer

Lower amperage

Answer

Same amperage

Answer

The compressor cannot run at 208V

Question 4

Which component in a residential AC control circuit prevents the compressor from restarting immediately after it shuts off?

Accepted Answer

Time-delay relay (anti-short cycle timer)

Answer

High-pressure switch

Answer

Capacitor

Answer

Contactor coil

Question 5

A homeowner reports the AC runs but does not cool. You measure 240V at the contactor load side and hear the compressor hum briefly then shut off. The MOST likely cause is:

Accepted Answer

Open start capacitor

Answer

Shorted run capacitor

Answer

Faulty thermostat

Answer

Low refrigerant charge

Question 6

What does a megohmmeter (megger) test on a compressor motor measure?

Accepted Answer

Insulation resistance between windings and ground

Answer

Winding resistance in ohms

Answer

Capacitor microfarad rating

Answer

Supply voltage quality

Question 7

On a residential split system, the 24V control transformer secondary is protected by an inline fuse. If the fuse blows repeatedly, the FIRST diagnostic step should be:

Accepted Answer

Check for a short circuit in the low-voltage wiring

Answer

Replace the transformer with a higher VA rating

Answer

Install a larger fuse

Answer

Check refrigerant charge