HVAC Test - Journeyman practice exam test 2 of 4 Assessment

Step 1: Safety first

Before starting, turn off the power to the HVAC system at the main circuit breaker to avoid accidents.

Step 2: Discharge the capacitor [Cap]:

The best method is to use your meter or a resistor. Short across the capacitor terminals to discharge any remaining voltage.

Side Note:

How to identify AC capacitor terminals?

1. If not rusted, the lettering stamped on the Cap is best for identifying terminals.
   1. "C" = Common
   2. "HERM" = Compressor
   3. "FAN" = Fan
2. If the Cap manufacturer used colored insulators:
   1. Black = Common
   2. White = Compressor
   3. Green = Fan
3. By the number of spades on each connection on some Caps.
   1. 4 spades = Common
   2. 3 spades = Compressor
   3. 1 or 2 spades = Fan

Use your multimeter on volts and "read" the voltage across the two terminals. The meter will safely bleed off the stored power, and you will see the voltage drop [drain]. But it is slow, about 1 minute for each capacitor in an HVAC dual capacitor. It takes two minutes. But, it's the safest way to drain a capacitor for both the technician and the capacitor's life.

Using a screwdriver seldom causes arching. But, it can damage plates and shorten the capacitor's 20-year life. Slowly drain the capacitor with a 20kΩ-5w resistor or a meter for safety. The resistor method is quicker than the meter method and the most common.

Step 3: Use a multimeter:

Use a multimeter. Set it to the highest resistance range and discharge the capacitor again. Then, place the multimeter leads on the capacitor terminals. Zero marks the starting point for resistance, which climbs upward to infinity. If the resistance remains at zero, the capacitor is shorted. If the capacitor is open, the resistance remains infinite (O.L.).

Step 4: Check the capacitance:

Check the capacitance. First, use your meter to verify that there is no voltage. Then, measure in MicroFarads. Set your multimeter to the capacitance setting. Then, connect the leads to the capacitor terminals. Compare the reading on the multimeter to the rated capacitance on the capacitor. The capacitor is faulty if the reading is much lower or higher than its rated capacitance.

Testing Capacitors FAQ:

Here are the three most frequently asked questions about testing capacitors.

Can I test a capacitor without a multimeter?

A multimeter is the best way to test a capacitor. No meter in hand? At least give it a visual inspection for signs of bulging or leakage. Those are signs of a faulty capacitor.

What happens if a capacitor is not working properly?

A faulty capacitor can harm the HVAC system. It reduces efficiency and may damage the motor or compressor.

What happens if a capacitor is not working properly?

It's good to test HVAC capacitors during regular maintenance. It's best to do this once a year.

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