Month: January 2019

I was talking about dry contacts with one of my techs and he was looking at me like I had three heads and one of them was on fire.

So I figured it would be good to cover the difference…

Basically “dry” contacts is a switch that has no shared power source or supply integral to the control. A common example would be the contacts in a compressor contactor. The contactor has a 24v coil (in residential) but the power supply through the contacts doesn’t have any connection to the coil.

We see wet contacts every day when we connect a residential thermostat. A thermostat uses the same voltage/power source to power the control that it passed to the contacts from the “R” terminal.

This is especially important to differentiate when working on commercial equipment that may have different and varied control. The Danfoss ERC 213 shown above is an example where the compressor (terminals 1 & 2) may be of a different voltage than the wet contacts on 5&6 which must be 120V.

Here is a video where I describe this in more detail –

—  Bryan

 

 

We all understand vacuum pump oil is the life-blood of our vacuum pumps. We know what the function of vacuum pump oil is, and how it functions. But how do we apply that knowledge when choosing the oil best suited for our pumps? Many of us simply pick up what’s in the stock room, or on the shelves at the parts house. However, there is a good possibility your stock room and suppliers don’t carry the correctly designed pump oil for our trade’s vacuum pumps. In order to understand the types of vacuum pump oil, here’s a quick review on the characteristics of pump oil:

  • Vapor Pressure

    • The lower the vapor pressure, the deeper the vacuum the oil is rated for

  • Viscosity

    • Medium viscosity (thickness) is used for warmer temperatures

    • Lower viscosity (thickness) is used for cooler temperatures

  • Distillation

    • The process of removing sulfur from mineral oil to refine the oil and reduce vapor pressure

It is important to understand distillation because distillation defines the application for which the pump oil is designed.

Single distilled oil is mineral oil that goes through a distillation process one time. The process reduces the sulfur content of the oil, and the resulting oil color is light brown. This oil is used for single-stage oil-sealed rotary vane pumps. The ultimate vacuum of single distilled oil is 10 microns (1 x 10-2 torr).

Double distilled oil goes through the distillation process a second time, further removing the sulfur content of the mineral oil. The resulting color is a lighter brown. This type of oil is designed for use on most two-stage vacuum pumps and has an ultimate vacuum of 1 micron  (1 x 10-3 torr).

    

Triple distilled oil goes through yet another molecular distillation process and is devoid of sulfur or other impurities. This oil is chemically inert and is highly resistant to oxidation and reactance to other gases. Triple distilled pump oil is transparent and is designed for an ultimate vacuum of 0.6 microns (6 x 10-4 torr).

Hydrotreated oil is a high-end pump oil designed for high vacuum applications, such as industrial and science. Hydrotreated oils are inert, and achieve a higher purity than any distillation process could boast. The process by which this oil is refined involves a hydrocarbon oil being combined with hydrogen under high pressure and temperature. This removes sulfur, nitrogen, and various other impurities from the oil. This type of oil is the purest oil available (as well as the most expensive), and is clear in color. The ultimate vacuum of hydrotreated oil is not important, as this is not an oil our trade uses. However, it is important to understand some drawbacks associated with hydrotreated oils, because I have seen companies use this highly expensive oil without fully understanding the characteristics.

Distilled vacuum pump oil is mixed with specific solvents, which aid in lubrication, oxidation resistance, and foaming resistance. These characteristics are important for vacuum pump oil, as they increase the life and performance of the pump and the oil itself. Hydrotreated pump oil, however, does not share the same solubility as distilled pump oil. This means hydrotreated oils do not mix with the necessary additives our trade specific vacuum pumps require. This can lead to damage to a vacuum pump and decreased vacuum efficiency, if not used in the appropriate application.

    

Synthetic (Perflouropolyether) oil is the final oil we will discuss here. This particular oil is very inert, and has a molecular consistent viscosity. The non-naturally-occurring molecules of synthetic oil are uniform in composition; whereas a typical distilled mineral pump oil has a viscosity based on the average molecule size. Synthetic oil is designed specifically for highly corrosive vacuum environments that contain gases like hydrogen peroxide, chlorine, hydrogen fluoride, etc.. If a distilled mineral oil were used in these applications, it would quickly break down and end up overheating the pump due to inadequate lubrication. This type of oil is not for use in our trade.

 All these different vacuum pump oils are designed for a specific application. Many of the suppliers in my area carry triple distilled pump oil, and it is on the shelves of many stock rooms. However, the ultimate vacuum triple-distilled oil is rated for is beyond the design of our trade specific pumps. Triple distilled pump oil is for use in pumps rated for continuous operation, not the intermittent operation we apply to our pumps. The typical HVAC/R technician will use either a single distilled, or double distilled pump oil. Single-stage pumps use single distilled oil, and two-stage pumps use double distilled oil. It’s fairly simple to remember. Both oils are cheaper than triple distilled oil anyway, so there is really no reason to carry triple-distilled oil on the truck or in the stock room. Next time you’re in the supply house, look at the rated viscosity and vapor pressure of the oil on the shelves.

Another vacuum pump fluid worth mentioning is flushing oil (fluid). Flushing fluid is basically a solvent oil containing high concentrations of the helpful additives already present in distilled mineral pump oil. This pump fluid can be used to clean the residual contaminants (water, oxides, etc.) from your pump leftover by the previous oil. Flushing fluid can be highly beneficial before and after use of the vacuum pump.

 In summary, there are many different types of oil used in vacuum pumps, and our trade must be aware of the type of oil we use in our trade’s specifically designed vacuum pumps. In order to optimize the full performance our pumps were designed to deliver, we may sometimes need question the unspoken norms. Constructive skepticism will push our trade to the next level of professionalism and overall growth.

   

Know your pump, know your oil. The performance and ultimate vacuum of your pump demands you keep the correctly design pump oil in its vanes…see what I did there?

– Kaleb

References:

https://vacaero.com/information-resources/vac-aero-training/24460-vacuum-pump-oil.html

www.edwardsvacuum.com

www.vacoil.com

Basic Compressor Functions

The job of the compressor is to circulate refrigerant through the system by means of vapor compression, similar to the way your heart moves blood through your circulatory system.

Refrigerant circulation is measured in lbs/min or lbs/hour; called mass flow rate. The mass flow rate changes depending on the density of the refrigerant and the compression ratio.

The denser (higher the pressure) the refrigerant is coming back from the evaporator the greater the mass flow rate and the lower the suction pressure the lower the mass flow rate.

The ability of the compressor to move refrigerant efficiently is often measured in volumetric efficiency. This is a measure of how much refrigerant enters the suction line vs. how much leaves the outlet of the compressor in the discharge line. The difference between the two is loss or waste to re-expansion of the gas in the compressor cylinder (in a reciprocating compressor).

The greater the compression ratio (absolute head pressure divided by absolute suction) the lower the mass flow rate will also be and lower the volumetric efficiency will be . In other words, low suction with high head pressure are the worst case scenario for mass flow rate and volumetric effeciency when the compressor is working as it should.

Proper lbs/min or lbs/ hour of refrigerant circulation is vital to the capacity of the evaporator, condenser and metering device as well as the cooling of th compressor if it is refrigerant cooled.

The Compressor size (pumping ability) controls the system’s lbs/min or lbs/hour mass flow rate.

Compressor pumping action also performs two other functions.

  1. It maintains the evaporator pressure: when the compressor runs, it lowers evaporator pressure. This sets evaporator pressure, operating TD, and BTUH capacity.

2. It increases condenser pressure: when a compressor runs, it pumps heat into the condenser, this causes condensing temp and TD to go up until heat can flow out of condenser as fast as it enters.

As evaporator heat load and temp increase, compressor heat output increases and drives condenser TD even higher to increase condenser heat rejection.

Compressor response to changing Evaporator heat loads

Here is a way of thinking about load and how it impacts mass flow rate, compression ratio and volumetric efficiency.

Higher heat loads produce vapor faster than compressor can remove it from the evaporator. When this occurs the evaporator pressure and temperature go up with the increased heat load.

The compressor’s flow in lbs/min or lbs/hr increases as the suction pressure increases and compressor draws more amps due to pumping more refrigerant.

Lower evaporator heat loads produce vapor slower than compressor is removing it from the evaporator. Evaporator pressure and temperature go down with the reduced heat load. Compressor’s flow in lbs/min or lbs/hour goes down. The Compressor draws fewer amps due to pumping less refrigerant.

Compressor’s Volumetric Efficiency

The goal is to keep the Volumetric Efficiency as high as possible. With a higher VE, a compressor produces more lbs/min or lbs/hour of refrigerant flow
Systems operating conditions, evaporating and condensing pressures, directly affects compressor pumping ability VE Ratio of Condenser pressure to evaporator pressure is called compression ratio. To calculate compression ratio, convert pressures to absolute values (add 14.7 to existing pressure) then divide condenser pressure by evaporator pressure

Volumetric Efficiency Charts

VE (Volumetric Efficiency) Charts show the effect of compression ratio on Volumetric Efficiency: As CR goes up, VE goes down. As CR goes down, VE goes up. Our goal is to keep volumetric efficiency of the compressor as high as possible for capacity, energy usage and compressor longevity.

Factors that determine system CR

System compression ratio is based on a few factors, primarily desired space temp and temperature of the cooling medium. Corresponding evaporator and condenser pressure establish the compression ratio the compressor must work against. Refer to the compression ratio chart for each compressor as a guide.

Keeping Volumetric Efficiency Up

In order to improve VE, you must keep the compression ratio low. You can do this by keeping condenser pressure low, maintaining clean condenser and supply it with a cool condensing medium (proper temperature and flow of air or water across the condenser coil or condenser HX). You must also keep the evaporator pressure up, don’t run the evaporator pressure any lower than needed to do the job. Lower compression ratio allows the compressor to pump more lbs/min or lbs/hour through the system. Higher compression ratios reduce the compressor’s ability to maintain the desired mass flow rate.

Compressor Approved Application Range (operating range) 

Hermetic and semi-hermetic compressors are designed for specific evaporator temperature ranges. The range of evaporating temps varies by manufacturer and model and you will need to do some reading to be sure you have it right. Evaporator temperatures above maximum approved temperature results in motor overload; drawing excess amps and overheating. An evaporator temperature below the minimum approved application temperature will result in poor motor cooling due to a low lbs_hour flow rate.

Compressor Data Sheets

Data sheets show compressor performance in its approved application range. Data may be shown in a table or as performance curves, these tables or curves will show : capacity  mass flow rate, power and current. This can be used for design, proper commissioning and system diagnosis. Just keep in mind that the compressor when working properly is still at the mercy of system conditions, it is up to us to set it up for success.

Compressor Amp Ratings

Compressor amps change as the evaporator and condenser temperatures change. Under load conditions, the compressor could draw more than rated load amps and not necessarily be in any danger of motor overload. As long as the motor amperage drawn is well below trip amperage. Most compressors will run at less than rated load amps during normal conditions but may run high under heavy evaporator load. All of this can be found by looking carefully at the compressor charts or curves.

– Louie Molenda

 

 

 

Back in the “good old days” controls were all analog and mechanical which simply means that they acted in a directly connected and variable manner based on a change in force. Both pneumatic (air pressure) or hydraulic (fluid pressure) systems are examples of mechanical, analog controls. When pressure increased or decreased on a particular device it signaled a change in action on another device like a pump/valve etc…

In the HVAC/R industry, we still see these types of controls with a TXV being a common example. The TXV is controlled by pressures in the suction line, bulb and spring to set the outlet superheat. These forces are all mechanical without electrical inputs or specific “data points”. The feedback from these forces is in constant tension to output the proper amount of refrigerant to properly feed the evaporator coil.

Digital vs. Analog

As controls have changed from mechanical to electrical we now have systems that are controlled by analog electrical signals and digital electrical systems. Analog is simply a varying electrical signal (either voltage or amperage) that signifies changes in a system or device. A digital signal means data encoded into “digits” which can be communicated using many different computer languages, rules or protocols (these all mean essentially the same thing). In digital controls the “signal” can include a combination of voltage, amperage and On/Off changes to communicate between devices.

So what about 4-20ma?

When the industry started to change over from mechanical to electrical they created a protocol (set of rules) that controls could use that would still function in a similar way to the old pneumatic controls. They decided that the range would be  4ma(milliamps) as the bottom reference of any sensor and 20ma would be the top reference. If you were setting up a sensor to indicate the fluid level in a tank you would set the bottom output to 4ma (meaning empty) and the top output to 20ma (meaning full).

In the case of a pressure transducer, you set the top range to the max rating of the sensor to 20ma and the bottom pressure reading to 4ma… you get the point.

ma controls are great because of their simplicity and ruggedness. You supply power to a “sensor” (Actually a sensor/transmitter to be exact) and based on the measurement the sensor reports to the transmitter that produces a milliamp signal. This signal is connected to an input on the control that measures the amperage and converts that to a reading.

Because amperage is the same at all points in the circuit the 4-20ma circuit is not impacted by voltage drop or interference like a voltage sensing circuit. Because the “bottom” of the scale is 4ma the control can also sense the difference between an “out of range” condition below 4ma and an open circuit.

The downside of a 4-20ma control is that each device requires it’s own conductor. In digital controls, many devices can be controlled by a single conductor set or “trunk” making it much easier to route, configure and manage complex controls.

Testing 4-20ma Circuits 

There are two different ways to measure milliamps. One is to use a special milliamp clamp called a “process clamp meter” that allows reading the amperage without disconnecting wires. These meters are expensive and it is unlikely that a typical HVAC/R tech will have one.

The more common way it to use alligator clips on a quality meter set to the milliamp scale and connect in series with the circuit. this means you will need to disconnect a wire or terminal and put your meter in the path. This is the same way we test microamps on a gas furnace flame sensing rod only using the milliamp scale.

— Bryan

 

This article is written by longtime tech Shaun McCann sharing his experiences with a big problem in our trade. Thanks for this Shaun. 


I started in the HVAC business working for a small commercial union shop in the late ’80s. I left that job within a year and worked in the bar and restaurant business for many years. I went back to school and learned my trade ultimately landing a job with an outstanding company.

 

When I first got hired I was sent to work within the residential department doing new construction installation. I worked with a man who had gone through major trouble in his life and now had found god. He actually swore once then made an overly dramatic statement about how he does not normally swear. He often spoke about some land he purchased and his desires to utilize it for a bible study camp. He was also very active with his church.

 

The irony about this gentleman is I watched him put a great deal of effort into stealing from the company and in some ways his coworkers.

 

When I first started the service manager had placed new company tools on a cart for my van. This guy took it upon himself to swap out the tools with his older ones. He went as far a telling me he was instructed to do so with one item. He would later teach me about how we should leave early but also should put down a full days work on our timesheet as that’s just how it worked. Amazingly he was a wolf in sheep’s clothing touting the Bible yet robbing the company in every way he could while making justifications for his actions.

 

I really enjoyed my job and newfound career. I made mistakes but worked hard to correct them and looked forward to advancement. 

Six months in I was called in for a review. I was told by my service manager ” You are one of the fastest, no you are the fastest new hire we have ever had work on his own ” he added ” I see no reason we shouldn’t put you in the union and I will send you for the next test “.

 

I remember my excitement and calling my girlfriend to share the great news! The next test was just a few months away.

 

The few months came and passed and nothing happened. A coworker knew I was upset and I explained why. Being a friend he mentioned my feelings to the service manager and the service manager stated he never said that. I approached the service manager later and was told: ” I do not recall saying that “. I walked away from that in complete confusion. I’ve now learned when you hear ” I don’t recall ” or ” I believe ” the lie is often being constructed directly in front of you.

 

The check is in the mail

 

 I later talked with my service manager and got him to commit to placing me in the union as the test was coming up the following month. When it came time I was told ” I’m not sure what happened as the union never received my letter ” I  basically lost it and was assured I would be going to the next test.

 

Finally, I was able to join the union.

 

The years that followed I worked on accounts others wanted no part of and I was lied to or manipulated constantly. I had a technician call the office to get me out to a building and saying the customer specifically wanted me when the customer called them. The aforementioned happened consistently. 

 

My purpose is to look into why many in this trade become amazing liars and (hopefully) how to prevent it. 

 

I think it would be fair to say there are people in our trade that entered as liars and those that became liars and some that walk the line and try to do the right thing but are hobbled by others ability to lie. 

 

Why we lie 

 

Fear

Companies come in all shapes and sizes and more importantly different company cultures. A manager may like to keep his employees in constant fear as a means to maintain productivity. A manager may want competition amongst employees and believes the workforce not getting along is good for the bottom line. 

 

I attended a class once where the seasoned instructor talked about a job he did and forgot to install a critical metal ring. He immediately spoke of not wanting to have to tell his boss of his need to return. I was amazed by a tech of his caliber not being able to admit his mistake. Everyone makes mistakes, no one is perfect and it really is a part of the business. 

 

Laziness – We just don’t want to be bothered. We are tired and maybe too busy outside of work. 

Lack of care – Let me get my eight and run home. 

Getting ahead – We like making others look bad or stay away from things that are too challenging so we always shine.

 

Covering up for others – We don’t want to make others look bad including the company.

Putting our customers at ease – Probably the number one thing that makes a truthful person into a liar.

Omission – Sometimes it’s the things we leave out that can cause the most harm.

 

I can say I have worked with a lot of liars in my day but never the caliber of the HVAC business and I find that disheartening. Teamwork is spoken of in meetings but often it goes out the window once it ends.

 

I strive to be part of a team and work towards a common goal but often that is just not possible. I instead try to go to work every day and do my job to the best of my ability.

 

Lying is like a drug that you consume more of as to increase the end result in your favor. Lying behavior can be easy to spot by voice inflection and other body movements however some people are amazing at it.

 

When you first start in the trade you make mistakes and slip up on a diagnosis or repair and you don’t want to damage the integrity of the company. Every technician has worked on something and said he fixed it but walked away hoping he fixed it.

 

Do we tell that to our customers? Normally not. Walking away with a customer thinking you kind of fixed their equipment is frowned upon. The lies grow from there. The noise you don’t notice at 2:30 on a Friday? The ” it was not doing that when I was there ” line. One of my favorites ” I was not involved with that project or repair ” so they get someone else. 

 

The number of lies and manipulations I’ve caught people in that I just absorbed and moved on from is staggering. I am certain to some I am perceived as naive but I realized early on it was easier to do the task and let the liar think they fooled me. The fact is my earnings were positive and I learned.

 

The funny thing is we know who the liars are around us but we cannot remedy them. We just accept it and counter their lies with our lies. Hence the cycle continues. There are times throughout our career where we make mistakes, others make mistakes or the company makes mistakes. The unfortunate thing is we must in some regard remain silent to remain employed and retain customers. 

The main thing we must accept is the lies will not cease.

 

We must look beyond and view the bigger pictures. A lot of these people will filter thru the company and you will not have to deal with them directly. Keep your cards close to you until you get a feel for those around you. Limit the amount of personal information you share with a coworker you are working with on any given day. Technicians work alone a lot and thus they seem to talk when working together. Try to remain on point until you have a relationship with someone beyond the one day task. The manager who lies constantly warrants two solutions. The first being to accept it, and the second seeking new employment. 

 

A word of caution

 

You will find some of the biggest liars are highly entrenched in an organization. Engaging them constantly and complaining about their manipulations and half-truths will make you stand out as the problem so beware of the path you are about to travel. 

 

On a final note, knowledge is key! The more training you get the less the lies affect you. You need to rely on others diminishes proportionally to your abilities and increases the confidence you have in your repairs and decisions. The higher confidence level trickles down to the office and customer perception of you. 

Most of all… Just tell the truth and break the chain

– – Shaun

So many techs are OBSESSED with how to set a charge rather than understanding all of the readings, specs and system conditions that go into optimum system performance.

Before ‘setting the charge” I suggest (nay… I REQUIRE) that you do a full visual inspection of the system, have an understanding of the initial factory charge and as installed line length and measure all of the “5 Pillars” on a continuous basis.

Charging or “setting the charge” is all about getting the right amount of refrigerant in the system, not about adjusting the charge to try to make up for some other system or installation issue (as is commonly the case). If there is another issue you want to fix it at the source before charging (“nip it in the bud” as Barney Fife says).

Once you check all of those things + verify airflow (when possible/practical) then it’s time to “set the charge” and sometimes you do that by superheat, most specifically on fixed metering device systems in the cooling mode.


First off…

Superheat is almost always a valid reading to take, but that doesn’t always make it a primary charging indicator. With a TXV or EEV metering device the superheat is controlled by the metering device itself so you can’t use superheat as the method to know when you have the proper amount of refrigerant in the system.

I know what many of you are thinking already…

I Just Want the Answer of How to Set Superheat!!!

But trust me… that isn’t ALL you want or need to know. You need to know WHEN to set the charge by superheat and what it means before I tell you HOW to do it.

Join me down this wormhole will you?

What does Superheat Tell Us? 

Superheat is heat, measured in degrees of temperature a vapor refrigerant GAINS above the boiling or saturation temperature (dew point in a blend). In order for a fluid (in this case refrigerant) to be superheated it must be completely changed to vapor.

The compressor is only designed to compress vapor refrigerant, so the first role of measuring superheat is to be certain that we HAVE superheated vapor going into the compressor rather than refrigerant in the saturated (part liquid) state.

The amount of superheat we have is also important. A superheat that is too low risks going to zero and causing compressor damage by flooding the compressor. A superheat that is too high means that the evaporator coil is being in being underfed with refrigerant which will lead to low capacity and efficiency as well as compressor overheating on most compressors.

Both high and zero superheat readings are very bad for the compressor so we need to make sure we get it within the design range.

How to Calculate Superheat?

Forgive how basic this is but we need to be clear on how to measure superheat before we can decide what it should be.

  1. Connect an accurate pressure gauge to the vapor (suction) side of the system, somewhere between the evaporator and the compressor
  2. Convert that pressure to a saturation (boiling) temperature or the dew point temperature in the case of a blend. This conversion may be built right into digital gauges, or it may be on a separate scale on analog gauges or you may use an app based or paper PT conversion chart to get the “saturation temperature”
  3. Take an accurate temperature reading at the same point (when possible) making sure the tubing is clean and the temperature sensor is making good contact with the line.
  4. Subtract the saturation (or dew point) temperature from the actual line temperature to get your superheat (temperature gained above the boiling point) at that point

In order for this process to work at all you need –

  • An accurate, calibrated pressure gauge
  • An Accurate, calibrated thermometer
  • Good contact between the thermometer and the line
  • Proper conversion from pressure to saturation temperature

There are actually three different types of superheat measurement that all serve different purposes. They all use the method listed above but they are measured at different points.

Evaporator Superheat 

Evaporator superheat is measured at the outlet of the evaporator. This method of measuring superheat is most useful when setting or checking TXV or EEV operation because the job of the TXV is to set the superheat at the evaporator outlet where the bulb or sensor is located. This is especially useful in refrigeration applications, especially in rack refrigeration applications where the superheat is measured at the case.

Advantage – Evaporator superheat tells us how well the evaporator is being fed which translates more accurately into evaporator, TXV and EEV performance

Disadvantage – Evaporator superheat does not tell us the state or temperature of the refrigerant before it enters the compressor. It also can’t be measured perfectly without the presence of a suction pressure port at the evaporator outlet which many split A/C systems do not have.

Total or Compressor Superheat

We most often measure superheat outside at the condensing unit before the compressor. This is more useful when setting the charge via superheat because we are more carefully controlling the superheat for long compressor life and because it is the easiest point to accurately set it.

Advantage – Compressor or Total superheat tells us the state and temperature of the refrigerant entering the compressor which helps us optimize for compressor longevity.

Disadvantage – The superheat at the coil may be different (generally lower) and may not be optimized for efficiency.

Discharge Superheat 

Discharge superheat isn’t used very often, but it is taken by comparing the temperature of the discharge line leaving the compressor to the suction saturation. This tells us the amount of heat that is gained not only in the suction line and evaporator but through the compressor. This measurement can be useful in checking compressor performance.

 

When do I charge with superheat? 

In air conditioning, you will be charging using superheat as the primary charging indicator when the metering device is a fixed or “piston” type

No! not THAT kind of piston

A piston is just a little piece of brass with a hole through it that can “seat” or “unseat” depending on the direction of refrigerant flow. The reason it is called a piston is because it can slide back and forth (in most cases) in this seated vs. unseated fashion.

Most manufacturers will have you charge a piston system in cooling mode using a chart or calculator where you first find the TARGET SUPERHEAT. To use the chart you will usually need.

  1. Outdoor dry bulb temperature taken in the shade
  2. Indoor return dry bulb and wet bulb temperatures

You will plug these into the chart or calculator and you will get a target superheat generally somewhere between 5 and 25 degrees.

Before you begin making charge adjustments!!!

  1. Check your other readings
  2. Visually inspect the system, especially the cleanliness of coils, filters, blower wheels etc..
  3. Let the system run at least 20 minutes to stabilize
  4. Be aware of the total system factory charge and line length
  5. Use a scale so you know exactly how much refrigerant you are adding or recovering

Now all you do is compare your measured superheat to the target (after you do all the other things I told you at the beginning)

  • If the target superheat is higher than your measured superheat your recover refrigerant
  • If the target superheat is lower than your measured superheat you add (charge with) refrigerant

Add refrigerant slowly and carefully. Blended refrigerants need to be charged as a liquid (tank upside down in most cases) so you need to take your time and throttle the refrigerant in to make sure no liquid is making it to the compressor.

Pause for several minutes periodically as you charge or recover to ensure you don’t overshoot and monitor all of your other system readings as you go.

There are many apps that make this easy that you can download on iPhone or Android that will help keep you from making mistakes.

  • MeasureQuick (The best diagnostic app on the market)
  • HVAC School App (Pretty good but I’m biased)
  • Testo Smart Probes
  • Fieldpiece Joblink
  • Emerson Check & Charge

Here are two videos showing the whole process using Fieldpiece and Testo probes. You will want to watch the first one…. it’s really good. And while you are at it can you subscribe to the Trutech and HVAC School youtube channels?

Remember…. target superheat is a MOVING target. As the indoor load changes and outdoor temps change the target will also change.

In order for you to get it right you need to have

  • Enough run time
  • Accurate tools
  • A dry condenser coil
  • Lots of patience

And even then getting to within 3° is about the best you can do.

— Bryan

This quick article is written by market refrigeration tech Clayton Peeples. Thanks Clayton


Adjusting the TXV should be done last after checking all other causes of the case being warm or flood back on the rack. Txvs very rarely go bad, generally, it’s a dirty screen or a failed powerhead which can be addressed without replacing the valve.

Before adjusting the TXV to raise the superheat you need to make sure that the screen is clean by pumping system down and checking the screen.

After the screen is clean and you have ensured that there is no ice in the case then you can start by checking the superheat with your digital gauges or probes.

If the superheat is at zero then it is best to start over using the following method to prevent floodback.

Danfoss  – Turn all the way in clockwise then go out 5 ¾ turns counterclockwise and let it set and equalize and then check after 15 mins.

Sporlan – Turn all the way in clockwise then go out 4 ½ turns counterclockwise and let it set and equalize then check after 15 mins.

The goal is a 6-12 degree superheat. When adjusting making minor adjustments and then let it sit and wait for adjustments to show. 

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