CRST Installation & Maintenance Practices 4 — Questions and Answers
Question 1: Which tool is used to measure the depth of a vacuum during system evacuation?
- Manifold gauge set
- Micron gauge (electronic vacuum gauge) (Correct answer)
- Compound gauge
- Anemometer
Correct answer: Micron gauge (electronic vacuum gauge)
An electronic micron gauge accurately measures deep vacuums in microns of mercury, which standard manifold gauges cannot resolve.
Question 2: A walk-in freezer door gasket is worn and not sealing properly. Besides temperature loss, what additional problem can result?
- Compressor overheating
- Excessive frost buildup on evaporator due to warm, moist air infiltration (Correct answer)
- Condenser coil icing
- Refrigerant migration to the liquid line
Correct answer: Excessive frost buildup on evaporator due to warm, moist air infiltration
Warm, humid air entering through a faulty door gasket increases the moisture load on the evaporator, causing excessive frost accumulation and longer defrost cycles.
Question 3: What is the recommended torque method for tightening flare fittings to avoid over-tightening and cracking the flare?
- Tighten until snug by hand, then one full turn with a wrench
- Use a calibrated torque wrench to the manufacturer's specification (Correct answer)
- Tighten as firmly as possible with two wrenches
- Tighten until the fitting stops rotating freely
Correct answer: Use a calibrated torque wrench to the manufacturer's specification
Manufacturer torque specifications applied with a calibrated torque wrench prevent both under-tightening (leaks) and over-tightening (cracked flares).
Question 4: During installation of a refrigeration system, the technician discovers the power supply voltage is 208V but the unit is rated for 230V. What should be done?
- Proceed with installation; the difference is negligible
- Install a step-up transformer or notify the customer that voltage must be corrected before startup (Correct answer)
- Rewire the unit internally to accept 208V
- Use a voltage reducer on the control circuit only
Correct answer: Install a step-up transformer or notify the customer that voltage must be corrected before startup
Operating a 230V-rated unit on 208V causes low-voltage conditions that can overheat motors and void the warranty; the supply voltage must be corrected.
Question 5: What is the function of a liquid line solenoid valve in a refrigeration system?
- Regulate suction pressure
- Pump down the evaporator when the system shuts off to prevent liquid migration (Correct answer)
- Control condenser fan speed
- Bypass the filter-drier during high flow conditions
Correct answer: Pump down the evaporator when the system shuts off to prevent liquid migration
A liquid line solenoid valve closes on shutdown to pump down the low side, preventing liquid refrigerant from migrating to the compressor crankcase.
Question 6: When pressure-testing a refrigeration system with nitrogen, what is the maximum test pressure typically used for medium-temperature applications?
- 50 psig
- 150 psig (Correct answer)
- 500 psig
- 1,000 psig
Correct answer: 150 psig
For medium-temperature systems, nitrogen pressure tests are commonly performed at approximately 150 psig, consistent with low-side design pressure ratings.
Question 7: A technician is installing a new TXV (thermostatic expansion valve) on a system. Where should the bulb be clamped?
- On the liquid line upstream of the valve
- On the suction line at the evaporator outlet, in good thermal contact (Correct answer)
- On the discharge line near the compressor
- On the suction line near the compressor inlet
Correct answer: On the suction line at the evaporator outlet, in good thermal contact
The TXV bulb senses suction line temperature at the evaporator outlet to control superheat, and must be clamped in firm thermal contact at that location.
CRST Installation & Maintenance Practices 4
Which tool is used to measure the depth of a vacuum during system evacuation?