CSLB HVAC (C-20) Trade — All Questions

Where may condensate from a residential cooling coil generally be discharged?

• a.Onto the ground directly beneath the outdoor condenser
• b.Into the crawl space provided a vapor barrier is already present
• c.Into a vent pipe serving a plumbing fixture
• d.To an approved location such as an indirect waste receptor✓

Condensate is treated as an indirect waste and must go to an approved receptor or point of disposal that prevents contamination and nuisance. Discharging into a plumbing vent obstructs the vent and violates its function. Random ground discharge under equipment creates a nuisance and can undermine the pad. And crawl-space discharge introduces continuous moisture under the building regardless of a ground cover.California Mechanical Code (Title 24, Part 4)

A furnace in an attic requires an unobstructed passageway to reach it. What else is normally required at the equipment?

• a.A ceiling-mounted smoke detector inside the enclosure
• b.A window or roof hatch within six feet of the appliance
• c.A fire extinguisher mounted within reach of the platform
• d.A level working platform, permanent lighting, and a receptacle outlet✓

Attic equipment must be reachable and serviceable, which means a solid working platform in front of the unit plus a light and a convenience receptacle for service tools. Smoke detection in the attic enclosure is not the servicing requirement. A mounted extinguisher is a good practice but is not what the access provisions call for. And no window or hatch adjacent to the appliance is required by the access rules.

You are setting an outdoor condensing unit on a new concrete pad. How should the pad be prepared?

• a.On loose topsoil so the pad can settle evenly with the surrounding ground
• b.Elevated on wood blocking to isolate it from ground moisture
• c.On compacted, well-drained soil so the unit stays level over time✓
• d.Sloped at least two inches toward the house for drainage

A pad on firm, drained subgrade keeps the cabinet level, which protects compressor oil return and proper condensate and fan operation. Loose topsoil settles unevenly and tips the unit. Sloping toward the house directs runoff at the foundation and tilts the equipment. And untreated wood blocking rots and shifts, leaving the unit unsupported.

A condenser is being installed 6 inches from a solid fence on the coil side. What is the practical consequence?

• a.The unit will short cycle on the low-pressure control
• b.Recirculated hot discharge air raises head pressure and cuts capacity✓
• c.The compressor will lose oil because of restricted suction
• d.The fan motor will overheat from a lack of ventilation air

Blocking airflow to a condenser coil forces the unit to re-ingest its own hot air, driving condensing temperature and head pressure up and capacity down. Fan motors on these units are cooled by the air they move and rarely fail first from tight clearance. Oil return is a piping and velocity issue, not a clearance issue. And low-pressure trips come from loss of charge or airflow on the indoor side.

Where must the disconnecting means for an outdoor air-conditioning condenser be located?

• a.Directly below the unit, within 12 inches of the pad
• b.Within sight of and readily accessible from the equipment✓
• c.Inside the building at the electrical panel serving the circuit
• d.Anywhere on the property provided it is padlocked

A technician working on the unit must be able to see and reach the disconnect, so it is installed within sight and readily accessible. A panel inside the house may be out of sight of the outdoor unit, allowing someone to re-energize it. A remote lockable disconnect alone does not satisfy the within-sight rule for this equipment. And there is no requirement fixing it a foot below the unit, which would also expose it to water and debris.California Electrical Code (Title 24, Part 3)

Low-voltage thermostat wire is being run alongside the line-voltage feeder in the same attic. What practice should be followed?

• a.Twist the two cables together so they support each other across the joists
• b.Run both inside the same flexible conduit for neatness
• c.Splice the low-voltage cable to the equipment ground for shielding
• d.Keep the classes separated and support the low-voltage cable independently✓

Class 2 control wiring is separated from line-voltage conductors and supported on its own so induced noise and insulation damage are avoided. Twisting them together puts the two classes in continuous contact. Sharing a raceway mixes voltage classes in a way the electrical code restricts. And connecting a control conductor to the equipment ground short-circuits the control circuit rather than shielding it.

On a conventional residential low-voltage control system, which terminal energizes the compressor contactor on a cooling call?

• a.W
• b.R
• c.Y✓
• d.G

The Y terminal carries the cooling call from the thermostat to the contactor coil at the condensing unit, which then closes and starts the compressor and condenser fan. W energizes the heat source, whether that is the gas valve circuit on a furnace or the sequencers on electric heat. G energizes the indoor blower independently of any heating or cooling call. And R is the transformer hot side that feeds all of the other calls rather than being a call itself.

A heat pump is installed with electric strip heat. How should the strip heat be controlled to protect efficiency?

• a.Wired directly to the W terminal in place of the compressor
• b.Energized with every heating call so recovery is fast
• c.Staged on only when the heat pump cannot satisfy the call✓
• d.Controlled by the outdoor fan relay so it follows defrost only

Auxiliary heat is a supplement, so controls bring it on only when the compressor falls behind or during defrost. Energizing it on every call wastes the heat pump's efficiency advantage entirely. Wiring it to W in place of the compressor turns an expensive heat pump into an electric furnace. And tying it only to the outdoor fan relay leaves the house without backup on the coldest hours.

Where should a wall thermostat be mounted in a typical residence?

• a.On an interior wall in a frequently used room, away from drafts and sun✓
• b.In the kitchen so cooking heat is detected quickly
• c.Directly above a supply register so it senses delivered air
• d.On an exterior wall near a window so it senses outdoor temperature swings

A thermostat should read average conditions in the living space, which means an interior wall in a used room and clear of sun, drafts, and appliance heat. An exterior wall conducts outdoor temperature into the sensor and gives false readings. A kitchen sees cooking heat that has nothing to do with the rest of the house. And mounting over a register makes the thermostat measure supply air and short cycle the equipment.

A furnace is installed in a downflow configuration on a combustible floor. What is required?

• a.Sheet metal flashing extending 12 inches beyond the cabinet
• b.A listed floor base or subbase approved for that furnace✓
• c.A two-inch air gap between the cabinet and the finished floor
• d.A layer of unfaced fiberglass insulation under the cabinet

Downflow furnaces discharge hot air through the floor, so the manufacturer's listed base or an approved subbase is required to protect the combustible construction. An arbitrary air gap is not a listed assembly. Loose flashing does not carry a listing and does not create the required clearance. And fiberglass under the cabinet is neither listed nor structurally suitable for the equipment.

What does the clearance to combustibles marked on a furnace rating plate represent?

• a.The minimum tested separation between the cabinet and combustible material✓
• b.The recommended distance for airflow around the cabinet
• c.The space needed in front of the unit to service the blower
• d.The distance the vent must be kept from the roof deck

Clearance to combustibles is a listed, tested distance that keeps adjacent wood and other combustible materials below their ignition temperature. Service clearance is a separate dimension driven by access to components. Vent clearances are specified for the vent system, not the cabinet. And it is a minimum safety requirement, not an airflow recommendation the installer may adjust.

Gas piping to a new furnace is being sized. Which set of inputs governs the pipe size?

• a.The total connected input BTU, the developed length, and the gas pressure✓
• b.The number of elbows and the diameter of the existing meter
• c.The furnace efficiency rating and the total number of appliances in the house
• d.The furnace output BTU and the length of the vent run

Gas pipe sizing tables are entered with the demand in BTU input, the developed length to the furthest outlet, and the supply pressure and allowable pressure drop. Output BTU understates the fuel actually drawn, and the vent run is irrelevant to gas sizing. Fittings are usually accounted for in the length allowance rather than counted individually against a meter diameter. And efficiency affects output, not the input the pipe must deliver.California Mechanical Code (Title 24, Part 4), Chapter 13

What is the correct arrangement for a sediment trap at a gas furnace?

• a.A horizontal extension of pipe upstream of the shutoff valve
• b.A flexible connector looped below the appliance inlet
• c.A capped vertical leg downstream of the shutoff and ahead of the appliance✓
• d.A capped tee installed above the gas valve inlet

The trap is a tee with a capped drop leg placed after the shutoff and before the appliance, so debris and moisture fall out of the gas stream by gravity. A horizontal extension gives particles no place to settle. A leg above the valve inlet works against gravity and traps nothing. And a looped flexible connector is not a sediment trap and may violate the connector's listing.

A flexible appliance connector is used to attach a furnace to the gas piping. Which practice is correct?

• a.Join two connectors together to reach the appliance
• b.Use one connector of adequate length without passing it through a wall✓
• c.Route the connector through a knockout hole in the furnace cabinet panel
• d.Conceal the connector inside the framed wall for appearance

A listed connector is used singly, in the open, and must not penetrate walls, floors, or appliance panels where it cannot be inspected or where it can chafe. Coupling two connectors together is specifically prohibited. Passing it through a cabinet panel exposes it to sharp edges and heat. And concealing it in a wall makes leak inspection impossible.

A furnace gas shutoff valve is being installed. Where does it belong?

• a.At the gas meter only, so one valve serves the whole house
• b.Downstream of the appliance regulator inside the cabinet
• c.In the attic above the furnace where it stays out of the way
• d.In the same room, ahead of the connector and within reach of the appliance✓

Each appliance gets an accessible shutoff in the same room, upstream of the connector, so gas can be isolated at the equipment. Putting it in an attic above a first-floor furnace defeats accessibility. Inside the cabinet downstream of the regulator it cannot isolate the appliance for service. And a meter valve alone shuts down the entire building rather than the one appliance.

After connecting gas piping to a new furnace, how should the joints be checked?

• a.Watch the gas meter dial for one minute with all other appliances running
• b.Hold a lit match near each joint and watch for flare-up
• c.Feel each joint by hand for the cold spot a leak produces
• d.Apply an approved leak detection solution or use an electronic detector✓

Approved bubble solution or a calibrated combustible gas detector finds leaks safely and precisely at each joint. An open flame at a suspected leak is an ignition source and is never an acceptable test. A leak large enough to feel is far beyond an acceptable one, and small leaks give no tactile clue. And watching the meter with appliances running cannot distinguish normal consumption from a leak.

Corrugated stainless steel tubing is used for a gas line to a rooftop unit. What additional installation step is commonly required?

• a.Supporting the tubing at intervals of no greater than 24 inches apart
• b.Bonding the tubing system per the manufacturer and electrical code✓
• c.Applying a corrosion-inhibiting coating to the jacket
• d.Sleeving the entire run in schedule 40 PVC

Corrugated stainless steel tubing is required to be electrically bonded to reduce the risk of damage from a lightning-induced arc. PVC sleeving is used for specific buried or penetration conditions, not as a general requirement. The factory jacket is the corrosion protection and is not field coated. And support spacing for this tubing follows the manufacturer's listing, which is generally more generous than two feet.

Sheet metal duct joints on a new supply trunk are being sealed. Which method is acceptable under current practice?

• a.Mastic applied over the joint, reinforced with mesh at wide gaps✓
• b.Silicone caulk applied only to the outside corners of the joint
• c.Standard cloth-backed duct tape wrapped twice around the joint
• d.Sheet metal screws alone, spaced no more than four inches apart at each seam

Mastic, with embedded mesh where the gap is wide, forms a durable air seal that stays flexible through thermal cycling. Cloth-backed duct tape dries out and releases, which is why it is not accepted for duct sealing. Silicone at corners leaves the seam itself unsealed. And screws are mechanical fasteners; they hold the joint but do not seal it.

How should flexible duct be supported between structural members in an attic?

• a.With wide straps at the manufacturer's spacing, limiting sag between supports✓
• b.By resting it directly on top of the ceiling insulation along its whole length
• c.With narrow wire ties every ten feet to allow natural sag
• d.With plastic strapping pulled tight enough to compress the liner

Flex duct is supported by straps wide enough not to pinch the liner, spaced per the manufacturer, with sag held to a small fraction of the span. Narrow wire ties cut into the jacket and create a restriction at each support. Laying the duct on insulation allows long uncontrolled sags and crushes the liner where it rests. And tight strapping that compresses the duct throttles airflow at every support point.

A flexible connector is installed between the air handler and the supply plenum. What is its purpose?

• a.To break the transmission of blower vibration into the duct system✓
• b.To relieve excess static pressure during blower startup
• c.To act as an access point for cleaning the supply trunk
• d.To provide an expansion joint for thermal movement of the sheet metal plenum

A canvas or listed flexible connector isolates blower vibration so it is not carried structurally into the ductwork and the building. Sheet metal duct does not need an expansion joint over these temperature ranges. It is not an access panel and should not be opened for cleaning. And it is airtight, so it does not relieve pressure at any point in the cycle.

A return duct is being installed in a two-story house. Which location must be avoided as a source of return air?

• a.A central second-floor hallway ceiling
• b.A living room wall about six feet above the finished floor
• c.A first-floor family room with a high ceiling
• d.A furnace closet containing a fuel-burning appliance✓

Taking return air from a room containing a fuel-burning appliance can depressurize that space and pull flue gases into the airstream. A second-floor hallway is a common and acceptable return location. A living room wall return is standard practice. And a family room with high ceilings is a normal return location, sometimes with a high and low grille for stratification.

Why is a building cavity such as a stud bay or panned floor joist no longer acceptable as a return duct in new work?

• a.It leaks to unconditioned space and cannot be sealed or verified✓
• b.It produces excessive velocity because the free area is too small
• c.It prevents the use of a washable filter at the grille
• d.It cannot be insulated to any R-value at all

Framing cavities communicate with wall, attic, and crawl spaces, so a negative-pressure return pulls in dust, moisture, and combustion products and cannot pass a leakage test. Free area in a stud bay is often generous, so velocity is not the core problem. Cavities can be lined, though poorly, so total inability to insulate overstates it. And filter type at the grille is unrelated to whether the cavity is sealed.

A supply duct passes through a rated fire wall in a small commercial building. What is generally required at the penetration?

• a.A volume damper set to the design airflow
• b.A listed fire damper installed per its listing✓
• c.A backdraft damper oriented with the airflow direction
• d.A flexible connector to allow movement

A listed fire damper installed with the required sleeve and retaining angles restores the rating of the assembly when duct penetrates it. A volume damper balances airflow and has no fire rating. A backdraft damper prevents reverse airflow and likewise carries no rating. And a flexible connector is a vibration break, which would actually be a weak point in a rated barrier.

Balancing dampers are being installed on a new branch duct system. Where should they be placed?

• a.Behind each register face where they can be adjusted from the room
• b.At the takeoff from the trunk, accessible for adjustment✓
• c.At the midpoint of each flexible branch inside the insulation
• d.Immediately downstream of the coil in the supply plenum

Dampers at the takeoff throttle the branch at its source, keeping generated noise well upstream of the occupied room and leaving the handle accessible. Register dampers make noise right at the occupant's ear and disturb the throw pattern. A damper buried mid-run in flex cannot be reached for balancing. And a single damper at the plenum throttles everything at once instead of balancing branches against each other.

A new air handler will use a 4-inch media filter instead of a 1-inch filter. What must the installer verify?

• a.That the return grille is at least twice the filter's face area
• b.That the filter media is replaced on the same schedule as a 1-inch pleated filter
• c.That the filter is installed on the discharge side of the blower
• d.That the cabinet has room for the rack and the blower can handle the drop✓

A deeper media filter needs physical space for a sealed rack and adds a pressure drop the blower must absorb without falling below design airflow. There is no rule requiring the return grille to be double the filter area. Filters belong upstream of the blower and coil so both stay clean. And a 4-inch media filter's whole advantage is a much longer service interval, so matching the 1-inch schedule is wrong.

A ductless mini-split indoor head is being mounted. What installation detail most affects condensate handling?

• a.The head must be mounted at least seven feet above the finished floor line
• b.The drain line must maintain continuous fall from the head to the outlet✓
• c.The line set must enter the wall below the level of the drain
• d.The head must be mounted level side to side within one degree

Mini-split heads drain by gravity through a small hose, so any rise or sag in that hose backs water into the pan and out the front of the unit. Mounting height affects throw and appearance but not drainage. The line set penetration is normally made below the head with the drain running alongside; its exact position relative to the drain is not the governing factor. And heads are typically pitched slightly toward the drain rather than dead level.

A multi-head mini-split system is being commissioned. Why does the manufacturer specify additional refrigerant beyond the factory charge?

• a.Because the outdoor unit ships with a partial charge only
• b.Because each indoor head must be individually pumped down
• c.Because multiple indoor heads increase the compressor's oil requirement
• d.Because line set length beyond a base allowance adds internal volume✓

The factory charge covers the outdoor unit plus a stated line length, and every foot beyond that adds volume that must be filled with refrigerant. Oil charge is handled separately by the manufacturer's oil specification. The units ship with a full charge for the base condition, not a partial one. And pumping down individual heads is a service procedure, not the reason for a charge adjustment at startup.

A rooftop packaged unit is being set on a new curb. What is the curb's primary function?

• a.To provide a weathertight, structurally supported transition for duct and unit✓
• b.To raise the unit above the parapet for better airflow
• c.To isolate the electrical supply from the roof membrane
• d.To serve as the required service platform around the unit

The curb ties into the roof structure and membrane, supports the unit, and forms the sealed opening through which supply and return ducts pass. Parapet height is unrelated to the curb's purpose. Electrical isolation is achieved with proper raceway and supports, not the curb. And service clearance around the unit is provided on the roof surface, not by the curb itself.

Equipment is being installed on a commercial roof more than 16 feet above grade. What access provision is normally required?

• a.A rope-and-anchor system at the parapet edge
• b.A roof hatch located within ten feet of the unit's main control panel
• c.A portable ladder stored on the roof next to the unit
• d.A permanent means of access such as a fixed stair or listed ladder✓

Rooftop appliances above the height threshold require a permanent, code-compliant means of access so service can be performed safely. A portable ladder is not a permanent means and can be removed or misused. Fall arrest anchors address edge work, not the climb to the roof. And there is no ten-foot hatch proximity requirement tied to the control panel.

A rooftop unit's economizer is being installed. What does the outdoor air damper control accomplish?

• a.It relieves supply duct static pressure during startup
• b.It uses cool outdoor air for free cooling when conditions allow✓
• c.It maintains a fixed minimum position at all times to reduce cycling
• d.It increases condenser airflow during high ambient operation

An economizer modulates outdoor air to meet the cooling load mechanically-free when the outdoor air is suitable, saving compressor run time. A fixed minimum position is only the ventilation floor, not the economizer's function. Condenser airflow is set by the condenser fan, which the economizer does not control. And static pressure relief is a barometric or powered relief function, not the economizer damper's purpose.

An energy recovery ventilator is added to a residence. Where should its exhaust intake be taken from?

• a.The attic, where the warmest air collects in winter
• b.The furnace closet, so appliance heat is recovered
• c.Rooms with the highest moisture and odor loads, such as baths and laundry✓
• d.The garage, where the air is already unconditioned

An ERV pulls stale air from the wettest, most polluted rooms and transfers its energy to incoming fresh air. Drawing from a garage would move vehicle exhaust and stored chemicals through the ventilator. Pulling from an appliance closet can depressurize it and interfere with venting. And attic air is outside the envelope, so exhausting it recovers nothing and only wastes fan energy.

A whole-house exhaust fan for continuous ventilation is being installed in a bathroom. Which specification matters most?

• a.The maximum speed setting listed on the fan carton
• b.The number of blades on the impeller wheel
• c.The rated airflow and sound level at the intended continuous setting✓
• d.The color and style of the ceiling grille

A fan that runs continuously must deliver its required CFM against real duct resistance and be quiet enough that occupants leave it on. The maximum boost setting is not the condition it will operate at. Grille appearance has no effect on ventilation performance. And blade count is a design detail that says nothing about rated flow or sound.

A bathroom exhaust duct is terminated in the attic instead of through the roof or wall. What is the consequence?

• a.The duct will collapse from the negative pressure it creates
• b.The exhaust airflow will exceed its rating without a proper termination
• c.Moisture is discharged into the attic, causing condensation and mold✓
• d.The fan will trip on thermal overload from backpressure

Exhaust must be carried to the outdoors, and dumping humid air into a cold attic condenses it on sheathing and framing. Backpressure at an open discharge is actually lower, not higher, so overload is not the issue. Airflow does not exceed the fan's rating simply because the duct is short. And an exhaust duct is under positive pressure downstream of the fan, so it does not collapse.

A supply register is being located in a bedroom in a cold California climate zone. Where does it generally perform best?

• a.Behind the door swing where it will not be blocked by furniture
• b.Near the exterior wall so the airstream washes the cold surface✓
• c.In the interior wall closest to the return grille
• d.In the ceiling directly above the bed for the shortest throw

Placing the supply at the perimeter lets the airstream counteract downdraft and cold radiation from windows and exterior walls. A register next to the return short-circuits supply air straight back to the system. Directly over the bed creates a draft complaint and does not address the cold surfaces. And behind the door swing is a location chosen for convenience, which usually blocks or misdirects the throw.

You are replacing a coil in an existing furnace cabinet. What matching issue must be verified?

• a.That the coil is rated for at least one ton more than the condenser
• b.That the coil has the same fin spacing as the one removed
• c.That the coil and condenser combination is a listed AHRI match✓
• d.That the coil casing is the same brand as the furnace cabinet

Rated capacity and efficiency apply only to certified combinations, so the coil must be an approved match for that outdoor unit and metering device. Brand matching alone does not guarantee a certified combination. Fin spacing is one design detail among many and does not establish a match. And deliberately oversizing the coil by a ton is not a listed combination and changes the refrigerant balance.

A replacement condenser uses a different refrigerant than the existing indoor coil and line set. What is the correct approach?

• a.Verify manufacturer approval and replace or properly clean the components✓
• b.Charge the new refrigerant into the existing coil and monitor operating pressures
• c.Flush the line set with refrigerant from the recovery machine
• d.Add a larger filter drier and reuse the line set as is

Different refrigerants use different oils and design pressures, so the manufacturer's instructions govern whether existing components may be reused, cleaned, or must be replaced. Simply charging a new refrigerant into an incompatible coil risks oil return failure and pressure problems. A larger drier does not remove incompatible oil from the tubing walls. And using recovered refrigerant as a flushing agent is not an approved cleaning method.

A residential system uses R-454B, an A2L refrigerant. What installation consideration does that class introduce?

• a.The equipment's listed mitigation features and charge limits must be followed✓
• b.The line set must be brazed using a silver-bearing alloy of at least 45 percent
• c.The system may be charged only in the vapor phase from the cylinder
• d.The outdoor unit must be installed at least ten feet from any window

A2L refrigerants are mildly flammable, so listed equipment carries charge limits, leak detection, and mitigation provisions that the installer must not defeat. Brazing alloy selection is driven by the joint and base metals, not by the refrigerant's safety class. Zeotropic blends like R-454B are charged as liquid to preserve composition, so vapor-only charging is wrong. And there is no blanket ten-foot window setback for the outdoor unit.

How should horizontal refrigerant lines be supported along a wall?

• a.By taping them to the adjacent condensate drain line every several feet
• b.Only at each end, allowing the run to hang free in between
• c.At regular intervals with hangers that do not crush the insulation✓
• d.By resting them on the top plate wherever they cross framing

Regularly spaced hangers sized to the tubing keep the lines from sagging and vibrating while leaving the insulation intact and continuous. Taping to a drain line transfers vibration and offers no real support. Resting tubing on framing lets it chafe and work-harden at each crossing. And supporting only the ends allows sag, vibration fatigue, and eventual joint failure.

Why is the suction line insulated on a split system while the liquid line usually is not?

• a.The liquid line is already insulated by its higher pressure
• b.Insulation on the suction line increases refrigerant velocity
• c.The cold vapor line would gain heat and sweat onto the building✓
• d.Insulation prevents the suction line from vibrating against framing

Suction vapor is below the dew point of surrounding air, so uninsulated tubing collects condensation and also picks up heat that raises superheat at the compressor. Insulation does not change velocity, which is set by mass flow and pipe area. Pressure does not insulate anything. And while insulation may cushion contact, vibration is controlled with proper supports rather than by wrapping the line.

A technician makes a flare connection on a mini-split service valve. Which practice produces a reliable joint?

• a.Overtighten the nut until the copper tubing visibly deforms against the seat
• b.Apply pipe dope to the flare face before tightening the nut
• c.Reuse the original flare from the removed unit to save time
• d.Deburr the tube, form a clean flare, and torque the nut to specification✓

A clean, properly formed flare tightened to the manufacturer's torque value seals metal to metal without cracking the copper. Overtightening splits the flare or extrudes it, creating a leak that appears later. Pipe dope is not a sealant for a flare fitting and can contaminate the system. And a previously compressed flare has already work-hardened and will not reseal reliably.

The service valves on a new condenser are still front-seated after the line set is connected and evacuated. What must happen next?

• a.Crack the liquid valve only and leave the suction valve closed
• b.Start the system and open the valves once suction pressure stabilizes
• c.Leave them closed so the factory charge stays isolated for shipping
• d.Open the valves fully to release the factory charge into the system✓

Once the line set and coil are leak tested and evacuated, both valves are opened fully so the factory charge fills the whole circuit. Starting a compressor with the valves closed runs it into a vacuum and can damage the motor. Leaving them closed means the system has no refrigerant available at all. And opening only the liquid valve starves the compressor while flooding the low side.

What vacuum level is generally accepted as the target before charging a new residential split system?

• a.5,000 microns held for one minute
• b.2,000 microns held for five minutes
• c.500 microns or lower, holding after the pump is isolated✓
• d.29 inches of mercury as read on a compound manifold gauge

A deep vacuum near or below 500 microns, verified by isolating the pump and watching for rise, shows that moisture and non-condensables are actually gone. Readings of 5,000 or 2,000 microns still leave water vapor in the system, and short hold times prove nothing. And a compound gauge lacks the resolution to distinguish 29 inches from a genuinely deep vacuum.

During evacuation the micron gauge falls to 400 but rises to 2,500 and levels off after the pump is valved off. What does that indicate?

• a.Moisture remaining in the system continuing to boil off✓
• b.A leak in the system or at the gauge connections
• c.A correctly evacuated system that is ready to be charged
• d.A vacuum pump with contaminated oil

A rise that stops and levels off means something inside is still vaporizing and then reaches equilibrium, the classic signature of residual moisture. A leak produces a rise that keeps climbing toward atmospheric pressure without leveling. Bad pump oil prevents reaching a deep vacuum in the first place rather than causing a leveling rise. And a system ready to charge holds close to its final reading with only a slight rise.

Why should the vacuum pump be connected with large-diameter hoses and both service ports open?

• a.To keep refrigerant oil from migrating into the pump
• b.To prevent the compressor from rotating during evacuation
• c.To reduce flow restriction so the system can reach a deep vacuum in reasonable time✓
• d.To allow the micron gauge to read pressure on both sides equally

At deep vacuum the gas is extremely thin and small hoses and valve cores choke the flow, stretching evacuation for hours or preventing it entirely. Oil migration is managed by pump design and isolation valves, not hose size. Nothing about hose diameter affects compressor rotation. And the micron gauge should be placed at the system, away from the pump, rather than averaging both sides.

A new system is being charged with a zeotropic blend. How should refrigerant be removed from the cylinder?

• a.As liquid, metered through the gauge set so it flashes before the compressor✓
• b.As liquid drawn directly into the suction service port
• c.As vapor from the top, to avoid slugging the compressor
• d.As vapor after warming the cylinder in hot water

A blend must leave the cylinder as liquid to keep its composition correct, and the technician meters that liquid so it vaporizes before reaching the compressor. Vapor charging a blend removes the more volatile component first and changes the mixture. Warming a cylinder in hot water is a dangerous practice and still charges vapor. And dumping unrestricted liquid into the suction port slugs the compressor.

What is the correct way to determine the final charge on a new TXV split system?

• a.Charge until the suction line sweats back to the compressor
• b.Weigh in the calculated charge, then verify with subcooling✓
• c.Charge to the pressure listed on the condenser's data plate
• d.Charge until superheat reaches ten degrees at the evaporator outlet

Weighing in the factory charge plus the line-length adjustment and then confirming subcooling is the manufacturer-supported method for a TXV system. Sweating on the suction line depends on humidity and tells nothing about charge. Data plates list electrical and capacity data, not a target operating pressure. And superheat is controlled by the TXV itself, so it cannot be used to judge charge on that system.

A crankcase heater is supplied with a new condensing unit installed in a cold climate. When should it be energized?

• a.After the system has reached steady-state operation
• b.Several hours before the compressor is first started✓
• c.Only while the compressor is running under load in cold weather
• d.Only during the defrost cycle on heat pump systems

The heater drives liquid refrigerant out of the oil, so it must run for hours before the first start to prevent a flooded start and oil foaming. Energizing it only while the compressor runs leaves the crankcase cold at the moment of highest risk. Defrost is a heat pump control sequence with a different purpose. And waiting until steady state defeats the entire point of preheating the oil.

A heat pump outdoor unit is being set in a location that gets winter frost. What mounting detail matters most?

• a.Tilting it slightly toward the house so water runs away from the fan
• b.Elevating it on a stand so defrost water drains clear of the coil✓
• c.Enclosing three sides to shield the coil from wind
• d.Setting it directly on grade so defrost water soaks into the soil

Heat pumps shed water during defrost, and elevating the unit keeps that water from refreezing under and into the coil. Sitting on grade lets ice build up around the base and block the bottom of the coil. Enclosing three sides restricts the airflow the outdoor coil depends on. And tilting the cabinet compromises compressor oil return and directs water at the structure.

Two condensing units are installed side by side against a wall. What clearance concern is specific to this arrangement?

• a.The condensate from one unit will drain into the other's base pan
• b.The shared electrical disconnect must be centered between them
• c.The refrigerant line sets must be routed above the units rather than below them
• d.Each unit can ingest the other's discharge air unless spacing is maintained✓

Side-by-side units placed too closely trade hot discharge air, driving both units' head pressure up and capacity down. Each unit requires its own disconnect within sight, so a shared centered device is not the issue. Line routing above or below is an installation preference with no bearing on clearance. And air-conditioning condensers do not produce condensate that could drain into a neighboring unit.

What is the purpose of the equipment ground conductor run with the branch circuit to a condensing unit?

• a.To provide the return path for the low-voltage control circuit at the board
• b.To carry the unbalanced load between the two hot legs
• c.To limit voltage drop over the length of the run
• d.To provide a low-impedance fault path so the overcurrent device opens✓

The equipment ground bonds the metal cabinet and gives fault current a low-impedance path back to the source so the breaker clears the fault quickly. Unbalanced load on a 240-volt appliance circuit is a neutral function, not a ground function. The low-voltage circuit has its own conductors and is isolated from the equipment ground. And voltage drop is managed by conductor size and length, not by the grounding conductor.