CFESA Test Equipment and Technical Documentation — Questions and Answers
Question 1: A technician is checking the combustion efficiency of a commercial gas range burner. Which instrument is used to measure flue gas oxygen (O₂) or carbon dioxide (CO₂) percentage for this analysis?
- Clamp-on ammeter
- Combustion analyzer (flue gas analyzer) (Correct answer)
- Manometer
- Thermocouple thermometer
Correct answer: Combustion analyzer (flue gas analyzer)
A combustion analyzer samples flue gas and measures O₂, CO₂, CO, flue temperature, and calculates combustion efficiency. This data is essential for verifying proper air-to-fuel ratio. Other instruments listed measure electrical current, gas pressure, or temperature — not combustion gas composition.
Question 2: When using a manifold gauge set on a refrigeration system, what does an abnormally high suction (low-side) pressure combined with a high discharge (high-side) pressure typically indicate?
- Low refrigerant charge
- Overcharge of refrigerant or a non-condensable gas in the system (Correct answer)
- A restricted liquid line filter-drier
- A failed compressor with low pumping capacity
Correct answer: Overcharge of refrigerant or a non-condensable gas in the system
Both high suction and high discharge pressures together indicate the system is working against excessive condensing load — most commonly caused by refrigerant overcharge or air/non-condensable gases trapped in the system (which raise head pressure without useful refrigeration effect). Low charge produces low suction AND low discharge pressure; restriction produces low suction and normal/high discharge; a weak compressor produces high suction and low discharge.
Question 3: A technician uses a clamp-on ammeter and reads 18A on a 208V single-phase motor nameplate-rated at 15A FLA. What is the correct interpretation?
- The motor is operating normally; clamp meters always read 20% high due to magnetic flux distortion
- The motor is drawing 20% above its Full Load Amperage, indicating a possible overload condition that should be investigated (Correct answer)
- The motor is underloaded; high amperage means the motor is running cool
- The reading is irrelevant unless the motor has tripped a breaker
Correct answer: The motor is drawing 20% above its Full Load Amperage, indicating a possible overload condition that should be investigated
FLA is the maximum continuous current rating for safe motor operation. Running at 120% FLA (18A vs 15A) elevates winding temperature, accelerating insulation breakdown. NEMA allows a 115–125% service factor depending on the motor, but this should be investigated — common causes include mechanical overload, low voltage, or a failing motor.
Question 4: On a ladder-style wiring diagram, what does a normally open (N.O.) contact symbol indicate about the contact's state when the controlling coil is DE-energized?
- The contact passes current when the coil is energized
- The contact passes current in its resting (coil de-energized) state
- The contact is open (no current flow) when the coil is de-energized (Correct answer)
- The contact requires manual reset after coil de-energization
Correct answer: The contact is open (no current flow) when the coil is de-energized
By definition, a Normally Open contact is open (circuit interrupted) in its normal, unactuated state — i.e., when the controlling relay or contactor coil is de-energized. It closes (allows current) only when the coil is energized. This is fundamental to reading ladder diagrams correctly.
Question 5: A technician needs to verify whether a heating element's insulation has broken down to the equipment chassis (ground fault). Which instrument is most appropriate?
- Standard digital multimeter set to continuity
- Megohmmeter (insulation resistance tester) (Correct answer)
- Clamp-on ammeter
- Non-contact voltage tester
Correct answer: Megohmmeter (insulation resistance tester)
A standard DMM measures resistance up to a few megohms with low test voltage (~9V), insufficient to stress the insulation as line voltage does. A megohmmeter applies 500–1000V DC and measures insulation resistance in the hundreds of megohms, revealing degraded insulation that would pass a DMM continuity check but fail in service. This is the correct tool for insulation integrity testing.
Question 6: When should a technician consult a manufacturer's Service Bulletin (TSB) in addition to the standard service manual?
- Only when the equipment is under active warranty
- When diagnosing a known recurring failure mode, identifying a superseded part number, or applying a factory-authorized repair modification not in the original manual (Correct answer)
- Only after the repair has failed twice using the standard diagnostic procedure
- Service bulletins are for sales staff only and do not apply to field technicians
Correct answer: When diagnosing a known recurring failure mode, identifying a superseded part number, or applying a factory-authorized repair modification not in the original manual
Technical Service Bulletins document field-discovered failure patterns, part number supersessions, firmware updates, and factory-authorized repair procedures that post-date the original manual. Skipping TSBs when diagnosing a chronic or recurring issue risks repeating a known failure pattern that the manufacturer has already identified and resolved.
CFESA Test Equipment and Technical Documentation
A technician is checking the combustion efficiency of a commercial gas range burner.
Which instrument is used to measure flue gas oxygen (O₂) or carbon dioxide (CO₂) percentage for this analysis?