High Superheat, Low Subcooling: Find the Leak

The short version

Superheat above target with subcooling below it means both coils are short of refrigerant at the same time. David Richardson, writing in Contracting Business, calls it the most common combination a technician will meet, and says the pair reveals a system low on refrigerant charge. The trap is treating “low on charge” as the diagnosis instead of the start of one, adding refrigerant, and driving away. The customer pays for that twice: the charge leaves through the same hole it left through before, so the no cooling call comes back, and every hour the system runs short of refrigerant is an hour the compressor runs at risk. Danfoss attributes a large number of compressor failures to loss of charge.

Prove the charge is low before you add refrigerant, because several faults push these readings the same way on a system that still holds all of it. A temperature probe reading the surrounding air instead of the pipe, flash gas in the liquid line ahead of the metering device, and a suction line that picked up heat on its way to the service port each account for part of what you are reading, and none of them is fixed by adding refrigerant. Flash gas is the easiest one to misread, because HVAC School describes the real cases as ones where subcooling at the condenser outlet still measures fine while the refrigerant flashes further down the line. Suction pressure and head pressure both reading below normal is the pattern that fits a real undercharge.

What the pattern means

Superheat is the actual suction line temperature minus the saturation temperature for the suction pressure. Saturation temperature is the temperature at which the refrigerant boils or condenses at the pressure you measured. Superheat measures how far the vapor warmed after the last liquid boiled off, so a high reading at the evaporator outlet means the boiling finished early and the rest of the evaporator had no liquid left to work on. Taken further downstream, the same number also carries whatever heat the suction line picked up on the way, which is a different fault with the same symptom.

Subcooling is the saturation temperature for the liquid line pressure minus the actual liquid line temperature. Bryan Orr at HVAC School gives the reading its job: “Subcooling tells us whether the liquid line is full of liquid or not. A 0° subcool reading tells us that the refrigerant in the liquid line is part liquid and part vapor.” A low reading means the condenser is not holding as much liquid as the design calls for, which HVAC School states as “not enough refrigerant is contained or ‘packed’ in the condenser.” It takes the zero reading Orr describes before the liquid line itself is carrying vapor.

Read together, the two numbers show the same thing about opposite ends of the system. Richardson states each half in a sentence: “In high superheat and low subcooling conditions, the high superheat tells you there isn’t enough refrigerant in the evaporator.” and “Low subcooling tells you there isn’t enough liquid refrigerant in the condenser.” He also sets the frequency: “High superheat and low subcooling are probably the most common combination you will encounter.”

That is what separates this pattern from a restriction. A restriction backs liquid up behind the blockage and starves the coil beyond it, so both readings climb together rather than splitting apart. Richardson states the pairing directly: “A system running high superheat and subcooling has a high-side restriction somewhere.” An undercharge leaves both ends short, because the refrigerant is not in the system to be moved anywhere.

Danfoss describes part of the same pattern from the compressor side. Its compressor checkup guidance, published for refrigeration and air conditioning service work, names two signs of a loss of charge at the gauges: “Look for a lower than normal suction pressure and high superheat.” That is the low side half of the pattern, and subcooling appears nowhere in the sentence.

Where you took each temperature determines what the number proves. At the evaporator outlet you read evaporator superheat. A thermostatic expansion valve (TXV) is the metering device that feeds the evaporator and holds superheat near a set value, and evaporator superheat is the number it controls. On the suction line at the condensing unit you read total superheat, which includes whatever heat the line picked up on the way, and a long or poorly insulated line set inflates it.

Subcooling has the same caution in the other direction. Read at the condenser outlet, it describes the liquid leaving the condenser. It does not describe the liquid arriving at the metering device, and on some systems the two are not the same.

Why a low charge is the first suspect

Orr organizes this diagnosis around five readings he calls the five pillars: suction pressure, head pressure, superheat, subcooling, and delta T, which is the temperature drop of the air across the evaporator. He is explicit that no single reading decides anything: “This list must be utilized by taking all five calculations and matching up the potential problems until you find the most likely ones.”

Run this pattern through his cause lists and one item appears under every reading. “Low on charge” is the first entry under High Superheat, under Low Subcooling, under Low Suction Pressure and under Low Head Pressure. Nothing else on those four lists appears on all four of them.

The near misses are worth naming, because they are the faults you would otherwise chase.

A liquid line restriction appears on the High Superheat and Low Suction Pressure lists, and Orr files it under high subcooling rather than low. Liquid stacks up behind the blockage instead of leaving the condenser, so subcooling rises.
“Compressor not pumping properly” and “Reversing valve bypassing (heat pump units)” appear on the Low Subcooling and Low Head Pressure lists, and neither one appears under High Superheat.
A metering device passing too much refrigerant appears under Low Subcooling and Low Head Pressure, and it drives superheat down rather than up.

This is an argument built on one publication’s lists, and Orr says so himself: “This is an incomplete list designed to help you. Always keep your eyes and ears open for other possibilities.” Use it to order your suspects rather than to close the call. What it points you toward next is suction pressure and head pressure, if you have not already read them. If suction pressure and head pressure are both below normal alongside the superheat and subcooling you already have, four readings fit a low charge. If head pressure is high instead, the four do not fit together, and something other than a plain undercharge is in the system.

Delta T narrows the field here rather than determining the answer. A narrow split fits an undercharge, and it also fits high indoor humidity, too much airflow, and a compressor that is not pumping, so it fits the case without proving it.

The faults that read the same way

Measurement error pushes both numbers this way at once. A liquid line probe left open to the air near a hot condenser reads warmer than the pipe, and subcooling is the saturation temperature minus that reading, so subcooling comes out low. A suction line probe doing the same thing reads warmer than the pipe, and superheat comes out high. One sloppy pair of clamps produces this exact pattern on a system that is charged correctly.

What you do about that depends on the instrument in your hand. A bead thermocouple strapped to a pipe needs insulation over it, because it is sitting in the air as much as on the copper. Fieldpiece makes a different claim for two of its clamp probes, the TC48 and the JL3LC: “with consistent clamping force and our patented Rapid Rail Sensor Technology, they are unaffected by ambient air, dust, paint, corrosion or moisture on the pipe surface.” That claim covers those two Fieldpiece clamps and does not transfer to another maker’s probe or to a thermocouple held on with tape.

Selecting the wrong refrigerant produces the same false pattern from a different direction. Every pressure you convert to a saturation temperature runs through a table specific to the refrigerant, so a manifold set to the wrong one gives you a superheat and a subcooling that never existed on that system.

Flash gas in the liquid line on a system with the right charge. Flash gas is refrigerant that boils in the liquid line before it reaches the metering device. Jeffery Staub, writing in HPAC Magazine, names the cause and the catch in one sentence: “An obstruction in the liquid line, such as a clogged filter drier or smashed or crimped liquid line tubing, can produce flash gas (see Figure 3), even though there is a proper refrigerant charge.”

Danfoss describes what that does to the valve: “Flash gas, or the formation of bubbles instead of liquid refrigerant upstream of the expansion valve, can lead to the expansion valve suddenly being too small for the system’s operating status, as the dimensioning is the basis for assuming fully liquid refrigerant at the expansion valve’s input.” A valve that is effectively too small starves the coil, which is the high superheat you are looking at.

Pressure drop in the liquid line does the same thing without any obstruction. Danfoss puts the design rule as “Low pressure drop prevents flash gas from forming,” and names the layout least exposed to it: “Hardly any flash gas formation can be expected with liquid lines flowing downwards and the expansion valve positioned far below the condenser/receiver.” Liquid that has to climb to reach the valve is the case at risk.

Staub gives the measurement that separates this case from a leak: “Check subcooling at both the condenser outlet and the TXV inlet prior to adding any refrigerant.” Subcooling that is healthy at the condenser and gone at the valve is a liquid line problem. Subcooling that is low in both places points back at the charge, once the rest of Orr’s Low Subcooling list is off the table: a metering device overfeeding, a compressor not pumping, a reversing valve bypassing, and a discharge line restriction are all on that same list.

High return air temperature. Orr lists it under High Superheat, and it applies on any call where the house started far above the thermostat setting. A house at 88°F puts a heavy load on the evaporator, and a fixed orifice cannot modulate to keep up, so superheat climbs. The charging chart already accounts for that load, though. HVAC School builds target superheat from the outdoor dry bulb and the current indoor wet bulb, and says target superheat rises as the wet bulb rises. So a hot house is a reason to take the wet bulb and read the chart at the conditions in front of you, not a reason to write the reading off. It also does not appear on Orr’s Low Subcooling list, so it does not account for the other half of this pattern.

A reversing valve bypassing internally, on a heat pump. Fieldpiece describes the fault plainly: “If your reversing valve has a leak inside, it’s splitting the refrigerant from the hot to the cool side.” Hot discharge gas mixing into the suction line raises the suction line temperature you measure, which reads as high superheat, while the low side pressure climbs and head pressure falls.

Fieldpiece puts the charge check ahead of the valve check: “Before you check to see if you have a leak inside your reversing valve, ensure that your system has the proper refrigerant charge.” Its test is a temperature comparison across the valve. In heating, “compare the temperatures of the suction line from the outside to the suction valve at the bottom. If the difference is more than 3°F, the valve needs to be changed.” Fieldpiece gives the same 3°F threshold for the cooling mode check.

A row below is a hypothesis, not a diagnosis. Let the system settle before you read it, and follow the procedure for the equipment where it gives one. AC Service Tech puts the wait at 10 to 15 minutes of runtime for a fixed orifice system and 5 to 10 minutes for a TXV, longer if the system was just opened or the charge was just adjusted.

Subcooling	Superheat	Suction pressure	Head pressure	Suspect	Confirm with
Low	High	Low	Low	Low charge, which means a leak	A leak search, then the weighed charge against the data plate after recovery
Normal to high	High	Low	Normal to low	A restriction between the condenser outlet and the evaporator	Temperature drop across the liquid line filter drier, which Carrier reads as a restriction in the filter itself, then the rest of the line and the metering device
Normal at the condenser outlet, low at the metering device inlet	High	Low	Normal	Flash gas from liquid line pressure drop or an obstruction	Subcooling read in both places, plus the route and size of the liquid line
Low	High at the condensing unit, normal at the evaporator outlet	Normal	Normal	Heat picked up in the suction line, or probes reading the air	A contact probe at the evaporator outlet, and both probes checked against each other on one spot
Low	High at the compressor	High	Low	A reversing valve bypassing internally, on a heat pump	The temperature difference across the reversing valve, with the charge verified first
Normal	High	Low	Normal	A metering device underfeeding the coil	The target for that metering device, against the manufacturer’s charging chart at current conditions
Normal	High	Normal to high	Normal	High return air temperature on a fixed orifice system	Indoor wet bulb and outdoor dry bulb, against the manufacturer’s charging chart

How to confirm it before you add refrigerant

Work in order. Each step costs less than the one after it, and every step is cheaper than a second trip.

Verify airflow before you trust anything the manifold shows you. Richardson puts airflow ahead of the gauges, calling it “the missing ingredient in refrigerant testing.” On a fixed orifice system low airflow drives superheat down rather than up, so it is not the explanation for the pattern in front of you. On a TXV system the valve works to hold superheat where it is set, and Richardson traces a hunting valve to poor airflow across the evaporator, which shows up as readings that will not sit still rather than as a clean high number. Either way it moves what you are about to record, and a system can carry an airflow fault and a leak at the same time.

Let the system run until the readings settle before you record anything. AC Service Tech puts that at 10 to 15 minutes of runtime for a fixed orifice system and 5 to 10 minutes for a TXV, and the equipment’s own procedure governs the wait where it gives one. Make it longer if the system was recently opened or the charge was recently adjusted. Readings taken in the first few minutes describe a system that has not settled.

Read the refrigerant off the data plate and select that refrigerant on your instrument. Do this before you convert a single pressure, because the saturation temperature for the wrong refrigerant makes both of your calculations wrong in the same step.

Check your two temperature probes against each other. Clamp both to the same spot on the same pipe, let them settle, and read them. The gap between them is the uncertainty you are carrying into every superheat and subcooling number for the rest of the call.

Insulate a probe that needs it, and know which kind you have. A thermocouple taped or strapped to the pipe reads partway between the copper and the air around it unless you cover it. Fieldpiece’s Rapid Rail clamps are the exception it publishes for its own TC48 and JL3LC probes, not a general property of pipe clamps.

Compare the readings to the target for the unit in front of you, using the number that the metering device is charged by. Craig Migliaccio at AC Service Tech states the split: “If the metering device is a fixed orifice such as a piston or capillary tube, the refrigerant charge of the system can be checked with Total Superheat. If the metering device is a TXV then the refrigerant charge can be checked with Subcooling.” That split comes with an equipment limit on the same page: “If the outdoor unit has a single speed or two speed compressor running in second speed and the unit is not a Micro-channel coil, then Total Superheat or Subcooling can be used to check the charge.” Outside that description, variable capacity equipment included, the manufacturer’s method is what applies when you check the charge. Fieldpiece prints two rules of thumb, 8 to 12 degrees of superheat and “8-14 degrees below the temperature that gas turns to liquid to be in the safe zone to ensure only liquid is fed into the metering device.” A rule of thumb tells you whether to keep looking. The manufacturer’s literature for that equipment is what you charge against.

Take subcooling in two places on a TXV system. Staub’s instruction is to check it at the condenser outlet and at the valve inlet before adding refrigerant. This is the step that separates a system that has lost refrigerant from a system whose liquid line is flashing, and skipping it is how a good charge gets topped off.

Only then call the charge low, and go looking for the leak. Richardson’s line is the argument: “Refrigerant doesn’t disappear.” A system that is low has leaked, and the leak is the repair. This post stops at the diagnosis rather than working through detection methods, because finding the leak is a procedure in its own right.

What to do once you confirm a leak

Certification comes first, and the rule is federal. The Environmental Protection Agency (EPA) requires it at 40 CFR 82.161(a)(1): “Any person who could be reasonably expected to violate the integrity of the refrigerant circuit during the maintenance, service, repair, or disposal of appliances … containing a class I or class II refrigerant or a non-exempt substitute refrigerant must pass a certification exam offered by an approved technician certification program.” The same section carves out an apprentice who is “closely and continually supervised by a certified technician,” and persons whose only involvement is disposing of small appliances, MVACs and MVAC-like appliances.

The venting prohibition applies at every size of appliance. At 40 CFR 82.154(a)(1) the regulation states: “No person maintaining, servicing, repairing, or disposing of an appliance or industrial process refrigeration may knowingly vent or otherwise release into the environment any refrigerant from such appliances.” Nothing in that sentence depends on how many pounds the system holds. What the section does contain is a list of exempt refrigerant and end use pairings, along with an allowance at 82.154(a)(2) for de minimis releases during a good faith attempt to recover or recycle. Neither one licenses deliberately dumping a non-exempt refrigerant while you work on the system. Refrigerant that escaped through the leak during normal operation is a separate question, and the EPA places that outside the venting prohibition rather than inside it.

The federal leak repair rules are a different question, and an ordinary residential split system falls outside both. The requirement is in two rules, and each one leaves this equipment out by a different route. The older one at 40 CFR 82.157(a) says: “As of April 10, 2020, this section applies only to appliances with a full charge of 50 or more pounds of any class I or class II refrigerant or blend containing a class I or class II refrigerant.” The same paragraph adds that “the requirements of this section do not apply to appliances containing solely substitute refrigerants,” which leaves an R-410A or R-454B system out before charge size even comes up. Class I and class II are the ozone depleting refrigerants that 40 CFR part 82 lists, and a residential split still holding R-22 sits far under 50 pounds. The newer rule at 40 CFR 84.106(a) covers appliances “with a full charge of 15 or more pounds of refrigerant” containing a regulated substance or a substitute with a global warming potential above 53, and it applies “as of January 1, 2026.” It then carves out an exception that covers this equipment by name: the requirements do not apply to “Refrigerant-containing appliances used for the residential and light commercial air conditioning and heat pump subsector.”

Read those two together and a residential split system is outside both repair requirements, on refrigerant class and charge size for the older rule and by name for the newer one. Being residential is not by itself what puts it there. That is a statement about what the EPA requires, not about what the job requires. The customer still paid for refrigerant that is now in the atmosphere, and it will happen again on the same schedule.

Recover before you open the circuit. The requirement is at 40 CFR 82.156(a): “Before opening appliances (except small appliances, MVACs, and MVAC-like appliances) or disposing of such appliances, technicians must evacuate the refrigerant, including all the liquid refrigerant, to the levels in Table 1 using a recovery and/or recycling machine certified pursuant to § 82.158 unless the situations in paragraphs (a)(1) or (2) of this section apply.” MVAC is motor vehicle air conditioning. Small appliances, MVACs and MVAC-like appliances are excepted from that paragraph rather than from the rule: 82.156(b) has its own recovery requirement before a small appliance is opened, and 82.156(c) has one for MVAC-like appliances.

Identify the refrigerant before you bring any heat near the system. This is the step on the list that injures a person rather than damaging a part. Copeland’s guidance for technicians working on systems charged with flammable refrigerants is direct about the tool: “Never use a torch to remove compressor components or tubing. Always use tubing cutters.” The same page tells you where to look first: “One of the first steps in safely working on a system is to identify the refrigerant used in the system and whether it is flammable,” and “The system nameplate indicates the type of refrigerant intended for use in the system.” It adds a second marking to check, one that warns a flammable refrigerant may be present rather than naming it: “Systems using flammable refrigerants should be colored red at the refrigerant process tubing and service ports.”

Copeland also sets a qualification ahead of the work: “EPA certification is not enough. Servicing HVAC/R systems with flammable refrigerants requires additional certification.” Its instruction to anyone without that training is to stop rather than open the system. When refrigerant is coming out on purpose, Copeland’s rule is that “If flammable refrigerants are purged from the system, use recovery equipment designed for use with flammable refrigerants.” A release you did not plan is a different response, and Copeland treats it as one: “If combustible levels are detected at any point in the process, then STOP service, ventilate and evacuate the area.”

Weigh the charge in after the repair rather than charging to a reading. Recover, repair, evacuate, then weigh in the charge the data plate gives, adjusted for the line set according to the installation instructions for that equipment. A weighed charge does not depend on the outdoor temperature or the indoor load holding still while you work.

Read the system again before you leave. Superheat should come down as the evaporator gets fed and subcooling should come up toward the target. Superheat that stays high after a correct weighed charge means the charge was never the fault, and the flash gas and restriction cases above are where to go next.

Look at what the low charge already cost. Danfoss puts a large share of compressor failures on loss of charge: “Loss of charge is responsible for a large number of failures and can be easily ascertained during this checkup.” It adds a check you can make with your eyes: “Check the compressor for discoloration on the head and by the discharge line. This can indicate that the compressor is experiencing excessively high discharge temperatures.” Danfoss publishes that as general compressor checkup guidance rather than as a limit for one brand, so take the operating limits for the compressor in front of you from its own manufacturer.

Common mistakes

Read suction pressure and head pressure alongside superheat and subcooling, because an undercharge and a high-side restriction both move all four readings and the combination is what separates them: the restriction drives subcooling up while an undercharge drives it down.
Check your two temperature probes against each other on the same spot before you act on either reading, since the suction line probe sets superheat and the liquid line probe sets subcooling, and a sloppy pair produces this whole pattern by itself.
Select the refrigerant from the data plate on your instrument before you convert any pressure to a saturation temperature.
Take subcooling at the condenser outlet and again at the metering device inlet on a TXV system, which is Staub’s instruction in HPAC Magazine and the measurement that finds a flashing liquid line.
Verify airflow before you trust the manifold, because Richardson calls it the missing ingredient in refrigerant testing and a system can carry both faults.
Identify the refrigerant from the nameplate before any heat comes near the system, read red process tubing and service ports as a warning that a flammable refrigerant may be present rather than as the name of which one, and recover to the levels the EPA requires before you open it.

Don’t

Add refrigerant to a system before you have established that the refrigerant actually left it, since flash gas and probes reading ambient air both produce this pattern on a full charge, and a bypassing reversing valve distorts a heat pump’s readings enough to look like one.
Treat topping off a leaking system, the gas and go, as a repair. Richardson’s own account of doing it is that “90% of the time, I was back within a week on another no-cooling call.”
Judge the charge against a memorized superheat or subcooling range when the equipment’s literature carries a target for that model at those conditions.
Charge a conventional TXV system by superheat, because AC Service Tech puts fixed orifice systems on total superheat and TXV systems on subcooling, within the conventional equipment its rule is written for.
Use a torch on tubing before you know what refrigerant is in the system, which Copeland rules out outright for flammable refrigerants in favor of tubing cutters.
Record readings in the first few minutes of runtime, before the system has settled.

Frequently asked questions

What does high superheat with low subcooling mean?

It means the evaporator and the condenser are both short of refrigerant at the same time, which usually means the system has leaked. David Richardson, writing in Contracting Business, states the two halves as “the high superheat tells you there isn’t enough refrigerant in the evaporator” and “Low subcooling tells you there isn’t enough liquid refrigerant in the condenser,” and calls it the most common combination a technician will meet. Treat it as a hypothesis until suction pressure and head pressure agree with it. Suction pressure and head pressure both below normal fits an undercharge, and a high head pressure alongside this pattern does not.

Can a system read high superheat and low subcooling without being low on charge?

Yes, and there are at least three ways. Temperature probes sitting in the air rather than on the pipe read the liquid line warm and the suction line warm, which lowers subcooling and raises superheat at the same time. It takes both of them to produce both halves, since superheat comes off the suction line probe and subcooling off the liquid line one.

Flash gas in the liquid line starves the metering device on a system with a full charge, which Jeffery Staub in HPAC Magazine attributes to an obstruction or crimped tubing. On a heat pump, a reversing valve leaking internally sends hot gas into the suction line, and Fieldpiece says to confirm the charge before you test the valve for it.

Do I have to find the leak, or can I just add refrigerant?

Find the leak. The EPA prohibits knowingly venting refrigerant at 40 CFR 82.154(a)(1) with no threshold on appliance size, and while the federal leak repair requirements at 40 CFR 82.157 and 40 CFR 84.106 both leave an ordinary residential split system out, 82.157 on refrigerant class and charge size and 84.106 by naming the subsector, the refrigerant you add leaves the same way the last charge did. Richardson’s account of topping off a leaking system instead is “Whenever I did a ‘gas-n-go’ to get the customer cooling again, 90% of the time, I was back within a week on another no-cooling call.”

Do I charge by superheat or subcooling?

By superheat on fixed orifice systems and by subcooling on TXV systems, on the conventional equipment that rule is written for. Craig Migliaccio at AC Service Tech states it as “If the metering device is a fixed orifice such as a piston or capillary tube, the refrigerant charge of the system can be checked with Total Superheat. If the metering device is a TXV then the refrigerant charge can be checked with Subcooling.” The same page limits that to a single speed compressor, or a two speed compressor running in second speed, on a unit without a microchannel coil. Either way, the target comes from the manufacturer’s literature for that equipment at the current conditions, and published rules of thumb are for deciding whether to keep looking.

What does running a system low on charge do to the compressor?

Running a system low on charge puts the compressor at risk, and Danfoss lists loss of charge among the failures worth checking for directly: “Loss of charge is responsible for a large number of failures and can be easily ascertained during this checkup.” Its visual check is discoloration on the compressor head and near the discharge line, which it reads as a sign of excessively high discharge temperatures. Danfoss publishes that as general compressor checkup guidance, so treat the temperature limits for the compressor in front of you as its own manufacturer’s question.

Glossary

AC Service Tech: a practitioner training organization cited here on charging method.
Class I and class II refrigerants: the ozone depleting refrigerants listed in 40 CFR part 82.
Contracting Business: a trade publication cited here on the undercharge signature.
Copeland: a compressor manufacturer, cited here for its flammable refrigerant service guidance.
Danfoss: a components manufacturer, cited here on compressor checks and expansion valve sizing.
Delta T: the temperature drop of the air across the evaporator coil.
EPA: Environmental Protection Agency, which sets the certification, venting and recovery rules cited here.
Fieldpiece: an instrument manufacturer, cited here on clamp probes and reversing valves.
Fixed orifice: a metering device that cannot adjust, such as a piston or a capillary tube.
Flammable refrigerant: a refrigerant that can ignite, which Copeland says calls for certification beyond the EPA’s.
Flash gas: refrigerant that boils in the liquid line before it reaches the metering device.
HPAC Magazine: a trade publication cited here on flash gas and where to measure subcooling.
HVAC School: a practitioner training and reference organization cited here.
MVAC: motor vehicle air conditioning, which 40 CFR 82.156 handles outside the paragraph quoted here rather than exempting from recovery.
Saturation temperature: the temperature at which refrigerant boils or condenses at a given pressure.
Subcooling: how far the liquid refrigerant sits below its condensing saturation temperature.
Superheat: how far the refrigerant vapor sits above its evaporating saturation temperature.
Total superheat: superheat measured on the suction line at the condensing unit, including heat the line picked up.
TXV: thermostatic expansion valve, the metering device that meters refrigerant to hold superheat.

Drafted with AI assistance and reviewed by the author.

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