HVAC Electrical Controls 3

Question 1

A motor starting capacitor (electrolytic) differs from a run capacitor (film/oil) in that it is rated for:

Accepted Answer

Intermittent duty only — seconds per start

Answer

Start capacitors are electrolytic and designed for intermittent use only; leaving them in circuit continuously will cause them to overheat and fail.

Question 2

When testing a run capacitor with a digital capacitance meter, an acceptable reading is typically within what percentage of the nameplate rating?

Accepted Answer

±6%

Answer

Industry standard allows run capacitors to be within ±6% of their rated capacitance; readings outside this range indicate a failing capacitor.

Question 3

What is the purpose of a lockout-relay (anti-short-cycle timer) in a refrigeration control circuit?

Accepted Answer

Prevent the compressor from restarting too quickly after shutdown

Answer

An anti-short-cycle timer delays compressor restart (usually 3–5 minutes) to allow pressure equalization and prevent motor overload from rapid cycling.

Question 4

In a heat pump system, the 'O' or 'B' terminal on the thermostat controls the:

Accepted Answer

Reversing valve solenoid

Answer

The O (or B) terminal energizes the four-way reversing valve solenoid, switching the refrigerant flow direction between heating and cooling modes.

Question 5

A technician measures 0 VAC across a normally-open contactor contact set while the coil is energized. This indicates:

Accepted Answer

The contacts are closed and conducting normally

Answer

When contacts close and conduct properly, the voltage across them drops to near zero because there is no resistance across a good closed contact.

HVAC Practice Test

HVAC Practice Test

HVAC Electrical Controls 3