CSLB HVAC (C-20) Trade — All Questions

A fixed-orifice system is being charged on a hot day. Which method does the manufacturer specify?

• a.Match measured superheat to the target from the charging chart✓
• b.Charge until the sight glass in the liquid line clears
• c.Adjust until subcooling reaches 10 to 12 degrees
• d.Weigh in the nameplate charge without any field verification afterward

A fixed orifice cannot regulate flow, so superheat varies with load, and the target superheat chart based on indoor wet bulb and outdoor dry bulb is the correct field method. Weighing alone is valid only when the entire charge is removed and the line length is known. Subcooling is the TXV method and is not the primary check on an orifice system. And residential split systems rarely have a sight glass to read.

A system has a condensing saturation temperature of 120 F and a liquid line temperature of 118 F on a 95 F day. What does that suggest?

• a.An overcharge that is backing liquid into the condenser tubes
• b.A restricted metering device holding back liquid
• c.Normal operation with a healthy liquid seal
• d.A shortage of refrigerant or poor condenser heat rejection✓

Only 2 degrees of subcooling means the condenser is not filling with liquid, which points to low charge or a condenser that cannot reject heat. A healthy system on that day would show roughly 8 to 15 degrees of subcooling. Overcharge produces high subcooling because liquid stacks in the condenser. And a restriction downstream of the condenser would raise subcooling, not lower it.

What physical change occurs in the refrigerant as it passes through the metering device?

• a.Liquid absorbs heat and boils completely into saturated vapor there
• b.Vapor is compressed into a high-pressure liquid
• c.Superheated vapor is desuperheated and condensed
• d.Pressure drops sharply and part of the liquid flashes to vapor✓

The metering device creates a large pressure drop, and the liquid's own heat boils a fraction of it instantly, chilling the mixture entering the evaporator. Compression to high pressure is the compressor's job. Complete boiling into vapor happens across the evaporator, downstream of the metering device. And desuperheating and condensing occur in the condenser on the high side.

Why does subcooling matter at the inlet to the metering device?

• a.It lowers the compressor's discharge temperature directly
• b.It reduces the superheat the evaporator must produce
• c.It ensures a solid column of liquid so the device meters at its rated capacity✓
• d.It prevents oil from separating out of the refrigerant

A metering device is rated for liquid, and vapor bubbles in the feed reduce mass flow and starve the evaporator, so subcooling guarantees liquid arrives. Discharge temperature is governed mainly by compression ratio and suction superheat. Evaporator superheat is set by the metering device's control action, not by subcooling. And oil circulation depends on velocity and miscibility, not on liquid subcooling.

Which three forces act on a conventional thermostatic expansion valve diaphragm?

• a.Bulb pressure, evaporator pressure, and spring pressure✓
• b.Liquid line pressure, superheat, and subcooling
• c.Discharge pressure, suction pressure, and crankcase oil pressure
• d.Condenser pressure, ambient pressure, and spring force

The bulb's pressure opens the valve, while evaporator pressure and the adjustable superheat spring close it, and the balance sets superheat. Discharge and oil pressures act elsewhere in the system and never reach the diaphragm. Ambient pressure is not a control input to the valve. And superheat and subcooling are conditions, not forces acting on a diaphragm.

What is the purpose of the external equalizer line on a TXV?

• a.To limit the maximum operating pressure the valve will allow
• b.To return oil from the evaporator to the compressor
• c.To bleed pressure from the high side into the evaporator coil at every shutdown
• d.To sense pressure at the evaporator outlet, correcting for coil pressure drop✓

An external equalizer reports the pressure at the coil outlet so the valve controls superheat correctly despite pressure drop through a distributor and long circuits. Pressure equalization at shutdown is done by a bleed-type metering device or a hard start component, not this line. Oil returns through the suction line with refrigerant velocity. And maximum operating pressure limiting is a separate MOP charge feature.

A TXV is hunting, with suction pressure swinging every 30 seconds. Which cause should be checked first?

• a.A loose or poorly insulated sensing bulb✓
• b.A compressor with worn suction valves
• c.A partially blocked outdoor condenser coil
• d.An undersized liquid line filter drier

A bulb that is loose, on the wrong part of the line, or exposed to ambient air reads inaccurately and drives the valve into oscillation. A dirty condenser raises head pressure steadily rather than causing rapid cycling of the valve. A restricted drier starves the valve continuously instead of making it swing. And worn compressor valves reduce capacity smoothly without producing a 30-second oscillation.

How does an electronic expansion valve differ from a thermostatic expansion valve?

• a.It uses sensors and a controller to position the valve electronically✓
• b.It maintains a fixed orifice area independent of load
• c.It regulates head pressure instead of evaporator superheat
• d.It requires no superheat measurement to operate

An electronic valve reads temperature and pressure sensors and drives a stepper motor, giving faster and more precise control over a wider range. It still controls superheat, so it very much depends on measuring it. A fixed area is the defining feature of an orifice or capillary, not an EEV. And head pressure control is a separate function performed by other devices.

A residential heat pump's accumulator serves what function?

• a.Holding liquid on the suction side and metering oil back gradually✓
• b.Separating oil from refrigerant leaving the compressor
• c.Reducing the pressure of vapor entering the compressor
• d.Storing excess liquid refrigerant on the high side of the system loop

A suction accumulator catches liquid that returns from the coil, especially at defrost changeover, and feeds oil and refrigerant back to the compressor at a controlled rate. High-side liquid storage is the job of a receiver. Oil separation at the discharge is done by an oil separator. And nothing in an accumulator is designed to reduce suction pressure.

During heat pump defrost, what happens inside the system?

• a.The outdoor fan speeds up to blow frost off the coil
• b.The reversing valve shifts to cooling and the outdoor fan stops✓
• c.The reversing valve holds position while the metering device reverses
• d.Auxiliary heat is energized while the compressor stops

In a reverse-cycle defrost the valve shifts so hot discharge gas flows to the outdoor coil, and the outdoor fan is stopped so that heat melts the frost rather than being blown away. Speeding the fan would only cool the coil further. The compressor keeps running because it is the source of the defrost heat, though auxiliary heat may be added to temper indoor air. And it is the reversing valve, not the metering device, that changes the flow direction.

A demand-defrost control differs from a time-and-temperature control in what way?

• a.It eliminates the need for a defrost termination sensor
• b.It defrosts using electric heaters instead of reversing the cycle
• c.It runs a defrost cycle at every compressor start in winter
• d.It initiates defrost based on measured coil conditions rather than a fixed clock✓

Demand defrost compares coil and ambient temperatures or airflow indicators and defrosts only when frost has actually accumulated, saving energy and run time. Reverse-cycle defrost is used by both control types on residential heat pumps. Defrosting at every start would waste more energy than the timer approach it replaces. And a termination sensor is still needed to end the cycle when the coil is clear.

What does the compression ratio of a refrigeration system describe?

• a.Mass flow at the discharge divided by the mass flow at the suction
• b.Gauge discharge pressure divided by gauge suction pressure
• c.The volume of the cylinder divided by its clearance volume
• d.Absolute discharge pressure divided by absolute suction pressure✓

Compression ratio uses absolute pressures, so atmospheric pressure must be added to both gauge readings before dividing. Cylinder volume over clearance volume describes a mechanical design property, not the operating ratio. Using gauge pressures gives a number that changes meaning with altitude and is not the standard definition. And mass flow is identical at both points in a sealed steady-state system.

Why does a rising compression ratio reduce a compressor's capacity?

• a.Gas trapped in the clearance volume re-expands, reducing the vapor drawn in✓
• b.The motor loses torque as discharge pressure increases
• c.The metering device closes to protect against high pressure
• d.The refrigerant's latent heat of vaporization falls sharply as pressure rises

High-pressure gas left in the clearance space expands on the down stroke and occupies part of the cylinder, so less new vapor enters and volumetric efficiency drops. Motor torque follows the load rather than collapsing as pressure rises. Metering devices respond to superheat or pressure drop, not to protecting the compressor. And while latent heat does change with pressure, the volumetric efficiency loss is the dominant effect.

A scroll compressor is being replaced. Which characteristic distinguishes it from a reciprocating compressor?

• a.It compresses continuously with two mating spiral elements✓
• b.It tolerates a continuous liquid return without internal damage
• c.It requires no crankcase heater under any condition
• d.It can be operated in either rotational direction

A scroll uses an orbiting spiral against a fixed spiral, giving smooth continuous compression with few moving parts. It tolerates brief liquid slugs better than a reciprocating machine but is still damaged by continuous flooding. Three-phase scrolls are direction sensitive and will not pump if phased backwards. And crankcase heaters are still applied to scrolls in cold ambient applications.

What is the practical difference between liquid slugging and flooding in a compressor?

• a.Slugging occurs only at startup; flooding occurs only at shutdown
• b.Slugging is caused by low charge; flooding is caused by high superheat
• c.Slugging is a sudden incompressible charge of liquid; flooding is gradual liquid return diluting oil✓
• d.Slugging affects scroll compressors; flooding affects reciprocating compressors

Slugging is a mechanical event in which liquid enters the compression chamber and cannot be compressed, while flooding is the slower washing of oil from bearings by returning liquid. Both can occur at startup or in steady operation depending on the cause. Both failure modes occur in either compressor type. And low charge and high superheat produce overheating, which is the opposite of a liquid-related failure.

Polyolester oil is used with modern refrigerants. What handling precaution does it require?

• a.It cannot be used in systems that contain a liquid line filter drier
• b.It must be blended with mineral oil before use
• c.It must be stored below freezing to prevent separation
• d.It absorbs moisture rapidly, so containers stay sealed until use✓

Polyolester oil is hygroscopic and pulls water from room air within minutes, and that moisture forms acids in the system. Blending it with mineral oil defeats the miscibility it was chosen for. Refrigeration oils are stored at normal temperatures, and freezing is not a requirement. And a filter drier is exactly what these systems need to control the moisture the oil attracts.

Non-condensable gases have entered a system. What symptom is most characteristic?

• a.Suction pressure far below normal with high superheat
• b.Low head pressure with normal subcooling
• c.Head pressure higher than the condensing temperature would predict✓
• d.Compressor amperage well below rated load amps

Air occupies condenser volume and adds its own partial pressure, so head pressure reads high relative to the temperature the liquid line actually shows. Low suction with high superheat is a starvation symptom from restriction or undercharge. Low head pressure would mean the condenser is rejecting heat too easily, the opposite condition. And amperage rises rather than falls when head pressure is elevated.

How does moisture in a refrigerant circuit cause damage?

• a.It reacts with refrigerant and oil to form acids and can freeze at the metering device✓
• b.It coats the condenser tubes and blocks heat transfer
• c.It reacts with copper to plate the compressor bearings
• d.It raises the refrigerant's boiling point in the evaporator

Water combines with refrigerant and oil to produce acids that attack windings, and free water can freeze at the expansion device and block flow. Boiling point in the evaporator is set by pressure, not by trace moisture. Moisture stays in circulation rather than coating condenser tubes. And copper plating is a real failure but is a secondary effect of acid formation, not the direct mechanism of moisture damage.

What does a liquid line filter drier with a high pressure drop across it indicate?

• a.The compressor is producing excess discharge pressure
• b.The drier was installed with the arrow pointing correctly
• c.It is loaded with debris and is restricting refrigerant flow✓
• d.The system is overcharged and liquid is stacking behind the drier

A significant temperature or pressure drop across the drier means the media is plugged and is starving the metering device. Overcharge raises pressure throughout the high side without creating a localized drop across one component. Excess discharge pressure would show up at the compressor, not as a drop across the drier. And correct installation direction is a good thing, not something a pressure drop reveals.

Which EPA Section 608 certification type covers residential split-system air conditioners containing more than five pounds of refrigerant?

• a.Type I
• b.Type II✓
• c.Type III
• d.Apprentice

Type II certification covers high-pressure and very high-pressure appliances, which includes residential and commercial split systems and heat pumps. Type I is limited to small appliances charged with five pounds or less at the factory. Type III covers low-pressure chillers that operate below atmospheric pressure. And there is no apprentice category in the Section 608 certification scheme.40 CFR Part 82, Subpart F (EPA Section 608)

What is the difference between recovering and reclaiming refrigerant?

• a.Recovery restores refrigerant to new purity; reclamation only removes it
• b.Recovery requires certification; reclamation does not
• c.Recovery applies only to blended refrigerants; reclamation applies only to single-component ones
• d.Recovery removes refrigerant from the system; reclamation reprocesses it to a purity standard✓

Recovery simply means removing refrigerant into a container, while reclamation means processing it, usually off site, to meet a recognized purity specification. Certification is required to handle regulated refrigerant either way. The purity restoration definition belongs to reclamation, not recovery. And both processes apply regardless of whether the refrigerant is a blend or a single compound.40 CFR Part 82, Subpart F (EPA Section 608)

A technician plans to recycle refrigerant on site with a recovery and recycling machine. What does recycling accomplish?

• a.It cleans refrigerant by separating oil and passing it through filters and driers✓
• b.It certifies that the refrigerant now meets the published reclamation purity standard
• c.It converts one refrigerant into another compatible blend
• d.It removes all non-condensable gases and water to laboratory levels

On-site recycling reduces contaminants through oil separation and filtration or drying, and the refrigerant is returned to equipment typically owned by the same customer. Meeting a purity standard requires laboratory reclamation, which a field machine cannot certify. No field process converts one refrigerant into another. And a recycling machine reduces but does not eliminate moisture and non-condensables to laboratory levels.40 CFR Part 82, Subpart F (EPA Section 608)

A recovery cylinder is being filled. What fill limit applies?

• a.95 percent of the cylinder's rated capacity by weight
• b.80 percent of the cylinder's internal volume by sight
• c.100 percent as long as the cylinder is kept below 90 F
• d.80 percent of the cylinder's rated capacity by weight✓

Recovery cylinders are filled to no more than 80 percent by weight so liquid can expand without hydrostatically rupturing the cylinder. Judging volume by sight is not possible in an opaque steel cylinder and is not the standard. Filling to 95 percent leaves too little vapor space for thermal expansion. And keeping a full cylinder cool is not a substitute for the fill limit, since ambient conditions change in a truck.40 CFR Part 82, Subpart F (EPA Section 608)

Which practice is prohibited under EPA Section 608 when servicing an air conditioner?

• a.Recovering refrigerant into a certified recovery cylinder
• b.Using nitrogen to pressure test a repaired refrigerant circuit
• c.Knowingly releasing refrigerant to the atmosphere during service or disposal✓
• d.Adding refrigerant to a system that has a known small leak after the repair is made

Knowingly venting a regulated refrigerant during maintenance, service, repair, or disposal is the core prohibition of the rule. Recovering into a certified cylinder is exactly what the rule requires. Recharging after a leak is repaired and verified is permitted. And nitrogen pressure testing is a standard, allowed procedure that produces no refrigerant emission.40 CFR Part 82, Subpart F (EPA Section 608)

R-410A and R-454B are being compared for a residential change-out. Which statement reflects a real operating difference?

• a.R-454B operates at roughly twice the pressure of R-410A
• b.R-410A requires mineral oil while R-454B requires polyolester oil
• c.R-454B is classified A2L, so listed equipment includes mitigation features✓
• d.R-410A can be safely charged as vapor because it behaves as a single compound

R-454B carries an A2L safety classification for mild flammability, and equipment designed for it includes charge limits, sensors, or other listed mitigation. Their operating pressures are broadly similar, not double. Both use polyolester-type synthetic oils rather than mineral oil. And R-410A is a near-azeotropic blend that is still charged as liquid, not a single compound.

What does temperature glide mean for a zeotropic refrigerant blend?

• a.Saturation temperature changes across the coil at constant pressure✓
• b.The refrigerant loses capacity gradually as the system ages
• c.The blend separates permanently once it enters the evaporator
• d.The refrigerant's pressure changes while its temperature stays fixed

In a zeotropic blend the components boil at different temperatures, so saturation temperature rises through the evaporator even though pressure is nearly constant, and the technician must use the correct dew or bubble point value. Pressure changing at fixed temperature describes a different process entirely. Capacity loss over time is a maintenance issue, not a property of the blend. And the components mix again in the vapor phase rather than separating permanently.

Why must a zeotropic blend be charged into a system as liquid rather than vapor?

• a.Liquid charging is the only way to weigh the charge accurately
• b.Vapor charging removes the lighter component first and changes the blend✓
• c.Liquid charging is required to lubricate the compressor bearings
• d.Vapor charging cannot reach the pressure needed to fill the entire system

The components of a blend have different vapor pressures, so drawing vapor from the cylinder pulls off the most volatile component and leaves a different mixture behind. Cylinder pressure is adequate for vapor transfer in many conditions, so pressure is not the barrier. Oil is charged separately and does not travel with the refrigerant from the cylinder. And a scale weighs the cylinder accurately regardless of which phase leaves it.

A technician needs the saturation temperature for a measured pressure on an A2L blend. Where does that number come from?

• a.The rule that saturation temperature is 35 degrees below ambient
• b.The equipment nameplate's design pressure rating
• c.The pressure-temperature data published for that specific refrigerant✓
• d.The generic pressure-temperature scale printed on the manifold gauge face

Each refrigerant has its own pressure-temperature relationship, and blends additionally have separate bubble and dew point columns, so the specific published data must be used. A generic gauge scale covers only the few refrigerants printed on it. Nameplate design pressure is a structural limit, not an operating relationship. And there is no valid rule tying saturation temperature to a fixed offset from ambient.

What does latent heat of vaporization describe in the refrigeration cycle?

• a.The heat rejected as the vapor is desuperheated in the discharge line
• b.The heat stored in the compressor oil during normal operation
• c.The heat that raises the vapor's temperature after it leaves the coil
• d.The heat absorbed as refrigerant changes from liquid to vapor at constant temperature✓

Latent heat is the energy a refrigerant absorbs while boiling without changing temperature, and it is the mechanism that moves the bulk of the heat load. Heating vapor above its boiling point is sensible superheat, not latent heat. Desuperheating in the discharge line is also a sensible process. And oil is a lubricant, not a thermal storage medium in the cycle.

Two systems run at the same suction pressure, but one has 5 degrees of superheat and the other has 30. Which statement is accurate?

• a.The 5-degree system is at greater risk of compressor overheating
• b.Both systems must have the same evaporator capacity
• c.The 30-degree system is using more of its evaporator surface for boiling refrigerant
• d.The 30-degree system risks overheating; the 5-degree system risks liquid return✓

High superheat means the refrigerant boiled off early and the returning vapor is hot, while very low superheat means liquid may reach the compressor. High superheat wastes evaporator surface on sensible heating rather than using more of it for boiling. It is the high-superheat system, not the low one, that runs the compressor hot. And unequal superheat means unequal use of the coil, so capacity is not the same.

How does a compressor's discharge temperature respond to very high suction superheat?

• a.It stays constant, because the compression ratio governs it entirely
• b.It rises, because hotter suction gas enters the compression stroke✓
• c.It falls, because thinner vapor carries less heat
• d.It rises only if the condenser is also dirty

Return gas temperature is one of the two main inputs to discharge temperature, so hot suction vapor produces very hot discharge gas that can break down oil. Lower vapor density reduces mass flow but does not cool the discharge. Compression ratio matters but does not act alone. And the effect appears with a clean condenser as well, since it originates on the suction side.

A hermetic compressor motor is cooled by what in a typical residential system?

• a.The returning suction gas passing through the motor windings✓
• b.The outdoor fan blowing air over the compressor shell
• c.The liquid line passing back through the compressor housing wall
• d.The oil sump circulating through an external cooler

Suction-cooled hermetic compressors route return gas over the motor before compression, which is why chronically high superheat overheats the windings. Cabinet airflow provides some incidental cooling but is not the design cooling path. External oil coolers appear on large industrial machines, not residential hermetics. And the liquid line never passes through the compressor housing.

What is the primary function of a receiver in systems that have one?

• a.To separate oil from the discharge gas before the condenser
• b.To store liquid refrigerant so charge can vary with load✓
• c.To protect the compressor from returning liquid at startup
• d.To lower head pressure by adding condenser volume

A receiver holds a reservoir of liquid on the high side so the metering device always has liquid available as operating conditions change. Protecting the compressor from liquid on the suction side is the accumulator's job. Oil separation happens in an oil separator at the discharge. And a receiver does not add effective condensing surface, so it does not lower head pressure.

Head pressure control is applied to a system operating in cold outdoor conditions. Why is it needed?

• a.To prevent the compressor from overheating in low ambient
• b.To maintain enough pressure difference for the metering device to feed properly✓
• c.To keep the condenser fan running at full speed year round
• d.To prevent the suction line from freezing at the compressor

If head pressure falls too far, there is not enough pressure drop across the metering device to feed the evaporator, and the system starves. Compressor overheating is a high-superheat or high-compression-ratio problem, not a low ambient one. Head pressure control typically slows or cycles the condenser fan rather than keeping it at full speed. And the suction line does not freeze from low head pressure.

A capillary tube system reaches equilibrium during the off cycle. What does that mean for restarting?

• a.Pressures equalize, so the compressor can start against a low load✓
• b.Pressures stay split, requiring a hard start kit on every unit
• c.The metering device closes tightly to hold back the high side pressure
• d.The compressor must be started manually with a jumper

A capillary tube is an open restriction, so pressures equalize during the off cycle and the compressor faces a light starting load, which is why these systems often use lower-torque motors. Pressure does not stay split, because nothing closes the passage. Capillaries have no valve to close tightly. And no manual starting procedure is involved in normal operation.

An evaporator coil is icing over on an 80 F day with the system running continuously. What are the two most likely causes?

• a.Low airflow across the coil or a refrigerant undercharge✓
• b.High outdoor ambient or a dirty condenser coil
• c.Overcharge or a stuck-open reversing valve
• d.A failed crankcase heater or a loose thermostat anticipator

Icing means the coil is operating below freezing, which follows from too little heat reaching it or too little refrigerant boiling in it, so restricted airflow and low charge lead the list. Overcharge raises suction pressure and works against icing. A dirty condenser raises head pressure without dropping the coil below freezing. And crankcase or thermostat problems affect starting and cycling, not coil temperature.

How does an undercharged system produce a frozen evaporator?

• a.The condenser cannot reject heat, so the coil temperature drops
• b.Suction pressure falls until the saturation temperature is below freezing✓
• c.The metering device opens wider and floods the coil with cold liquid
• d.The compressor runs hotter and transfers some of that heat back to the coil

With too little refrigerant, suction pressure drops and the corresponding saturation temperature falls below 32 F, so condensate freezes on the fins. Compressor heat travels with the discharge gas toward the condenser, not backward into the evaporator. A condenser that cannot reject heat raises pressures throughout, which does not freeze a coil. And flooding the coil would raise suction pressure and coil temperature.

A technician finds a system that is overcharged. Which set of readings fits that condition on a TXV system?

• a.Low head pressure, low subcooling, and high superheat
• b.High head pressure, high subcooling, normal superheat✓
• c.High head pressure, low subcooling, and high superheat
• d.Low head pressure, high subcooling, and normal superheat

Extra refrigerant stacks in the condenser, so subcooling and head pressure both climb while the TXV keeps superheat near its setting. Low head pressure with low subcooling describes an undercharge. High head with low subcooling suggests non-condensables or a condenser problem instead. And high subcooling with low head pressure is an inconsistent combination on an operating system.

What is the purpose of a low-pressure control on a residential split system?

• a.To reverse the compressor when the coil begins to frost
• b.To stop the compressor when suction pressure indicates loss of charge✓
• c.To modulate the metering device as load changes
• d.To keep the evaporator from ever operating above its design pressure limit

A low-pressure switch opens when suction pressure falls below its setpoint, protecting the compressor from running with insufficient refrigerant. Preventing high pressure is the high-pressure control's role. Metering devices modulate on their own control inputs, not from a pressure switch. And no residential control reverses a compressor's rotation in response to frost.

A refrigerant leak is suspected in an attic coil. Which detection method is best suited to pinpointing it?

• a.Adding a can of sealant and monitoring pressures afterward
• b.Watching for an oil stain on the drain pan over the next several weeks
• c.Comparing the suction pressure before and after the coil
• d.An electronic leak detector swept slowly along the tubing and returns✓

A heated diode or infrared detector moved slowly along joints and return bends locates the leak precisely and is the standard field method. Oil staining is a useful clue but is slow and often absent on small leaks. Pressure drop across a coil reflects flow restriction, not leakage. And sealants can plug metering devices and driers and do not identify where the leak is.

A large leak has emptied a system. What must be done before the system is recharged?

• a.Install a larger metering device to restore capacity
• b.Add extra refrigerant to compensate for the loss
• c.Run the compressor briefly to circulate any oil left in the lines
• d.Repair the leak, then pressure test, evacuate, and verify✓

The leak has to be found and repaired, the repair proven with a pressure test, and the system evacuated to remove air and moisture that entered before the charge goes in. Simply adding refrigerant releases it again and is prohibited. Running a compressor with no charge damages it and does nothing useful. And changing the metering device does not address the loss of refrigerant or the entry of contaminants.

A compressor has burned out and the oil smells acidic. What service step protects the replacement compressor?

• a.Cleaning the system and installing a suction line filter drier and a new liquid line drier✓
• b.Installing a sight glass in the liquid line to monitor moisture
• c.Charging the system with 10 percent extra refrigerant
• d.Reusing the original filter drier after blowing it out with nitrogen

A burnout leaves acid and debris throughout the circuit, so the system is cleaned and both a suction line filter and a fresh liquid line drier are installed to capture what remains. Overcharging changes operating conditions and removes nothing. A moisture-indicating sight glass reports a condition but does not clean the system. And a used drier is already saturated and cannot be restored by blowing it out.

Which condition explains high suction pressure together with low head pressure on a cooling system?

• a.Worn compressor valves or an internal bypass in the compressor✓
• b.A dirty outdoor condenser coil
• c.A plugged liquid line filter drier
• d.An oversized metering device installed on an otherwise correct system

A compressor that is no longer pumping lets the two sides drift toward each other, raising suction while head pressure falls. A plugged drier starves the low side and drops suction pressure instead. A dirty condenser raises head pressure. And an oversized metering device floods the evaporator, raising suction pressure but not lowering head pressure.

How is a compressor's pumping ability verified in the field?

• a.By measuring the resistance of the run and the start windings when cold
• b.By measuring the voltage drop across the contactor
• c.By closing the suction service valve and observing how low it pulls✓
• d.By comparing the amp draw to the locked rotor amps

A closed-valve pump-down test shows whether the compressor can pull and hold a low suction pressure, which directly measures pumping capability. Winding resistance is an electrical check that says nothing about mechanical pumping. Contactor voltage drop tests the contact, not the compressor. And locked rotor amps is a starting characteristic, not a pumping measurement.

A heat pump in heating mode has the reversing valve stuck in the cooling position. What will the customer report?

• a.The system heats but never satisfies on the coldest days
• b.The outdoor unit runs but the indoor blower never starts
• c.The system heats normally but the defrost cycle never runs
• d.Cold air comes from the registers on a call for heat✓

If the valve does not shift, the indoor coil keeps acting as an evaporator and the registers deliver cold air while the thermostat calls for heat. Falling short on the coldest days is the normal behavior of a heat pump near its balance point. A blower that never starts is a control or motor fault. And a heat pump that heats normally is by definition shifting the valve correctly.

Which measurement best confirms that an outdoor condenser coil is rejecting heat properly?

• a.Static pressure across the outdoor coil
• b.Condensing temperature compared with the outdoor ambient✓
• c.Suction line temperature measured at the compressor inlet
• d.Amperage of the outdoor fan motor

A healthy air-cooled condenser condenses at a predictable margin above the entering air temperature, so comparing the two reveals fouling or airflow loss. Suction line temperature reflects evaporator and line conditions. Fan amperage indicates the motor is turning but not that the coil is clean. And static pressure is not a practical measurement across an open outdoor coil.

Why does a dirty evaporator coil reduce capacity even though the refrigerant charge is correct?

• a.It insulates the tubing, so the refrigerant leaves the coil as liquid
• b.It raises head pressure, which reduces compressor displacement
• c.It causes the metering device to overfeed and flood the compressor
• d.It restricts airflow, so less heat reaches the refrigerant and suction pressure falls✓

A blocked coil starves the refrigerant of heat, so boiling slows, suction pressure and coil temperature drop, and capacity falls. The refrigerant leaving a starved coil is heavily superheated vapor, not liquid. Head pressure actually tends to fall because less heat is being absorbed and moved. And a starved coil makes the metering device throttle back rather than overfeed.

What does the coefficient of performance describe for a heat pump?

• a.The percentage of input fuel converted to usable heat
• b.The ratio of heat output to energy input in consistent units✓
• c.The ratio of BTU output to watts input measured at rated conditions
• d.The seasonal average of heating output over a full winter

COP is a unitless ratio of energy delivered to energy consumed, and it can exceed 1.0 because a heat pump moves heat instead of creating it. Fuel conversion percentage describes combustion efficiency and cannot exceed 100 percent. A seasonal average across a heating season is HSPF, a different metric. And BTU per watt is the definition of EER, which mixes units rather than being unitless.

A service valve core is removed to speed evacuation. What is the risk if it is not reinstalled?

• a.The system will read a false high suction pressure
• b.The gauge hose cannot be attached to the port again
• c.The compressor will not build head pressure at startup
• d.The cap alone is the remaining seal, and refrigerant can leak past it✓

The valve core is the primary seal at a service port, and a cap is only a secondary seal, so an omitted core will leak the charge over time. Hoses attach to the port fitting whether or not a core is present. Suction pressure readings are unaffected by the core's presence. And nothing about a missing core prevents the compressor from building pressure.

Which practice reduces refrigerant loss every time gauges are connected and removed?

• a.Connecting only the low-side hose on every service call
• b.Leaving the hoses attached between visits to the same customer site
• c.Using low-loss hose fittings and recovering what the hoses hold✓
• d.Purging the hoses with refrigerant before connecting them

Low-loss fittings close the hose ends, and recovering the hose contents keeps the trapped charge out of the atmosphere. Using one hose does not eliminate the loss from that hose. Leaving hoses attached exposes them to weather and does not prevent loss at removal. And purging hoses with refrigerant deliberately vents it, which is exactly what the rules prohibit.