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Fabrication, Installation & Startup — California C-20 Practice Questions

88 questions · 38% of the C-20 HVAC Trade exam

Worked questions

4. May oxygen be used to pressure-test fuel-gas piping?

  • ANo gas piping is ever tested
  • BYes, with extra oil
  • CYes, above appliance rating
  • No; use the approved test medium and procedure

Why D is correct

Oxygen can react violently with fuel residues and materials. The code-specified inert or approved medium, pressure, isolation, and gauge must be used.

8. A wall sensor is above a copier and receives afternoon sun. How should the control-location problem be resolved?

  • ACover it with insulation
  • Relocate it to a representative location
  • CCalibrate it only at night for the described HVAC equipment and measured operating conditions
  • DIncrease equipment tonnage

Why B is correct

The best answer is: Relocate it to a representative location. Local heat and solar gain bias sensed temperature and cause poor comfort and cycling. The sensor must represent the controlled zone rather than an abnormal microclimate. The transferred operating condition requires the same design, installation, diagnostic, or safety principle in a different HVAC context. The other choices skip a prerequisite, conflict with the listed procedure, or treat a symptom without controlling its cause.

9. During smoke-control testing, the fan starts before the required dampers reach position. What must be corrected and retested?

  • Correct and functionally test the approved control sequence
  • BIncrease refrigerant charge for the described HVAC equipment and measured operating conditions
  • CRemove smoke detectors
  • DDisable status feedback

Why A is correct

The best answer is: Correct and functionally test the approved control sequence. Smoke control depends on coordinated fan, damper, pressure, alarm, and firefighter-control actions. Individual component operation does not prove system performance. The transferred operating condition requires the same design, installation, diagnostic, or safety principle in a different HVAC context. The other choices skip a prerequisite, conflict with the listed procedure, or treat a symptom without controlling its cause.

10. Landscaping blocks normal access to an outdoor unit disconnect. What electrical correction is required?

  • Provide the required rated and readily accessible disconnect
  • BUse the thermostat as the disconnect
  • CLabel a remote breaker only
  • DRemove grounding for access

Why A is correct

The best answer is: Provide the required rated and readily accessible disconnect. Service personnel need a readily accessible local means to isolate equipment as required. A control command is not normally an equipment disconnect. The transferred operating condition requires the same design, installation, diagnostic, or safety principle in a different HVAC context. The other choices skip a prerequisite, conflict with the listed procedure, or treat a symptom without controlling its cause.

11. Rigid duct weight is carried by the equipment's flexible connector. What support change is needed?

  • Provide independent supports without stressing the flexible connector
  • BUse the connector as a hanger
  • CIncrease fan horsepower
  • DSupport it from electrical conduit for the described HVAC equipment and measured operating conditions

Why A is correct

The best answer is: Provide independent supports without stressing the flexible connector. Flexible connectors isolate vibration and are not structural supports. Independent hangers protect joints, clearances, drainage, and equipment from imposed duct weight. The transferred operating condition requires the same design, installation, diagnostic, or safety principle in a different HVAC context. The other choices skip a prerequisite, conflict with the listed procedure, or treat a symptom without controlling its cause.

12. The access opening beside a smoke damper cannot reach its actuator or reset. What must change?

  • ACover the panel permanently for the described HVAC equipment and measured operating conditions
  • Provide usable access at the service location
  • CRemove the actuator
  • DRely on ceiling demolition

Why B is correct

The best answer is: Provide usable access at the service location. Dampers and other internal devices require inspection, testing, reset, and maintenance access. A nominal opening at the wrong location is not usable access. The transferred operating condition requires the same design, installation, diagnostic, or safety principle in a different HVAC context. The other choices skip a prerequisite, conflict with the listed procedure, or treat a symptom without controlling its cause.

13. What devices must control pressure between a nitrogen cylinder and the connected refrigeration circuit?

  • A suitable regulator and rated test setup
  • BA household air hose for the described HVAC equipment and measured operating conditions
  • CAn oxygen regulator
  • DNo pressure control

Why A is correct

The best answer is: A suitable regulator and rated test setup. Cylinder pressure can exceed system and gauge ratings. A compatible regulator, relief and rated hoses or manifold provide controlled test pressure. The transferred operating condition requires the same design, installation, diagnostic, or safety principle in a different HVAC context. The other choices skip a prerequisite, conflict with the listed procedure, or treat a symptom without controlling its cause.

75 more in the bank

Answers and explanations for these are in the app.

  • A condensate drain has flat and back-pitched sections. What should be done?
  • A condensing appliance vent has sags that trap condensate contrary to instructions. What is required?
  • A condensing furnace is connected to an existing metal chimney because the old furnace used it. What must control the new vent system?
  • A condensing furnace is installed out of level beyond its instructions. Why must it be corrected?
  • A duct access panel cannot reach a fire damper actuator. What must change?
  • A fire damper is installed backward and its access panel is blocked. What is required before concealment?
  • A fire damper sleeve is fastened so it cannot move as required by its listing. What should occur?
  • A flexible duct connector is pulled tight and carries duct weight. What is required?
  • A heat-pump thermostat is configured for conventional cooling. What should be corrected?
  • A mechanical room is made tighter after doors are weatherstripped. What must be rechecked?
  • A metal duct run sags and loads a flexible equipment connector. What should be done?
  • A negative-pressure cooling coil has an untrapped drain that pulls air inward and will not drain reliably. What is required?
  • A new hydronic loop has trapped air and no circulation through upper coils. What startup step is needed?
  • A new refrigerant circuit is ready for leak testing. Which medium is appropriate when used within equipment ratings?
  • A new supply plenum has visible unsealed joints before insulation. What is the proper sequence?
  • A rectangular duct joint deforms and leaks under test pressure. What should be corrected?
  • A rooftop unit is set but approved wind and seismic attachments are incomplete. May startup proceed?
  • A rooftop unit is set on a curb with gaps and out-of-level support. What should occur before connection?
  • A sealed duct system fails the required leakage test. What is the proper response?
  • A smoke-control fan starts, but dampers move in the wrong sequence. What is required?
  • A technician charges a variable-speed heat pump by sight glass alone, contrary to its instructions. What is required?
  • A thermostat is mounted in direct sunlight above heat-producing equipment. What should be done?
  • A three-phase compressor is about to be started after service changes. What should be checked?
  • A three-phase hydronic pump develops little flow after replacement. What should be checked first?
  • A three-phase supply fan runs backward at first start. What should be done?
  • A vacuum pump reaches the target micron level, but pressure rises rapidly when the system is isolated. What does that indicate?
  • Air bypasses a filter because the rack has large gaps. What is required?
  • An economizer is installed but its outdoor-air damper never opens during favorable conditions. What startup work is needed?
  • Before judging refrigerant charge, measured indoor airflow is far below the manufacturer’s required range. What should be done first?
  • Cold supply-duct insulation has torn vapor-retarder seams. What should be done?
  • Copper refrigerant tubing is being brazed with no nitrogen flowing through it. Why should the procedure be corrected?
  • Flexible duct is compressed, sharply bent, and unsupported across a long run. What correction is appropriate?
  • Measured airflow across a new evaporator is below its approved range. What should be corrected?
  • What equipment is essential between a high-pressure nitrogen cylinder and a refrigeration system?
  • What is the purpose of flowing low-pressure nitrogen while brazing refrigerant tubing?
  • What should be documented at equipment startup rather than simply noting that it runs?
  • Why must airflow and operating mode be correct before final charging?
  • A canvas connector is stretched tight and supports downstream duct weight. How should the assembly be rebuilt?
  • A combination fire/smoke damper is reversed and its service access is covered by drywall. What must happen before approval?
  • A condensing furnace exceeds the manufacturer's allowed tilt. Which operation may be impaired?
  • A drain line alternates between flat and uphill sections before reaching its receptor. What installation correction is required?
  • A long flex-duct branch is crushed behind framing and droops between widely spaced supports. Which correction protects airflow?
  • A new refrigeration circuit must be strength- and leak-tested without introducing moisture or oxygen. Which test medium and setup are appropriate?
  • A newly sealed duct network exceeds its permitted leakage rate. What should occur before ceilings are closed?
  • A newly started three-phase supply fan moves air backward. Which safe electrical correction is appropriate?
  • A rectangular supply trunk deforms and leaks at its transverse connection during pressure testing. Which fabrication details need correction?
  • A replaced three-phase circulation pump has little differential pressure. Which initial operating checks should be made?
  • A rooftop package rests on an uneven curb with a displaced gasket. Which conditions must be corrected before duct and utility connection?
  • A startup sheet says only “unit runs.” What measurements and functional evidence should replace that entry?
  • A supply plenum is insulated while transverse joints are still visibly open. What installation sequence should have been followed?
  • A technician suggests oxygen for testing a new fuel-gas line. Is that an approved test method?
  • A thermostat is programmed as conventional heat/cool even though it controls a reversing-valve heat pump. What needs correction?
  • A variable-capacity system is charged using only bubble appearance even though the startup chart specifies measurements. What controls the charge?
  • A VAV fan operates, but there is no record of terminal response, pressure reset, or control sequence. What demonstrates commissioning?
  • After deep evacuation, isolated pressure rebounds rapidly and continues climbing. Which conditions should the technician suspect?
  • Air bypasses around a loosely fitted filter bank. What should the installer correct before airflow testing?
  • Air sealing converts a furnace enclosure into a confined space. What must startup verify about appliance air?
  • An induced-draft coil drain draws air through an unprimed, shallow trap and fails to flow. What must be corrected?
  • An installer connects a condensing appliance to a masonry flue merely because the old furnace used it. Which venting basis controls?
  • An isolated evacuation rises modestly from 450 to 575 microns and then stabilizes. How should acceptance be decided?
  • Before starting a serviced three-phase compressor, which supply and rotation checks should be completed?
  • Black scale forms inside refrigerant tubing during brazing. Which procedure would have limited this contamination?
  • Cold-duct insulation has open seams in its exterior vapor retarder. What must be restored to prevent condensation?
  • Condensing vent pipe sags and holds liquid between supports. Which pitch and drainage corrections are required?
  • Fasteners through a fire-damper sleeve prevent the movement required by its listing. What controls the correction?
  • Field dimensions leave less service clearance than the packaged unit's listing requires. What should happen before it is set?
  • Indoor airflow is 30% below the permitted range when a technician begins checking superheat. Which problem should be corrected first?
  • Measured evaporator airflow is outside the approved operating range after startup. Which path and setup checks come first?
  • Outdoor conditions call for economizer cooling, but the damper remains closed. Which components and sequence require commissioning?
  • Refrigerant tubing vibrates against a sharp cabinet edge. How should it be protected and supported?
  • Upper hydronic terminals remain air-bound after filling. Which commissioning operation is needed?
  • Weatherstripping newly seals a room containing two atmospheric appliances. What air provision must be rechecked?
  • Why is low-pressure nitrogen flowed through clean copper while joining refrigeration piping?
  • Why should blower airflow and equipment mode be verified before final charge measurements are interpreted?
  • Wind and seismic anchorage is incomplete beneath an installed rooftop unit. May the contractor start it for testing?

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