HVAC School - For Techs, By Techs

Chris Stevens from HVACR Videos on YouTube comes onto the podcast and talks about some refrigeration temperature controls basics. You can check out his YouTube channel HERE. Although we have temperature controls in HVAC work, we will see slightly different ones in refrigeration work. The biggest difference is really the temperature itself; we're attempting to bring the box temperature down, so we will be dealing with much lower temperatures in refrigeration. The box and evaporator coil temperatures are the most important temperatures to be aware of in reach-in refrigeration, as they directly relate to pressures. A standard pressure control opens or closes when pressures fall or rise. Your typical low-pressure control will open on a pressure fall and close on a pressure rise. We can use these as loss-of-charge switches or use them with the pressure-temperature relationship as evaporator temperature controls. However, pressure controls can be quite inaccurate. You absolutely CANNOT "set it and forget it" with these controls; you will likely have to make some adjustments, especially if you have long line sets. We also need to consider defrost in our strategies. Constant cut-in controls are other common control strategies. These are simple controls with a sensing bulb in the evaporator coil that senses evaporator temperature as closely as possible without being a pressure control; they also turn on at a set temperature. These refrigeration temperature controls are quite accurate, but they can be difficult to use properly because they also pick up lots of other vital signs from the system. Chris and Bryan also discuss: TD vs. delta T K-type thermocouple calibration Wrap-up procedures for refrigeration jobs Self-defrosting with pressure controls Constant cut-in control sensing bulb placement Service gauges Frost buildup in medium-temperature applications Digital controls Controls based on product temperature Universal and aftermarket controls Air-sensing temperature controls   Learn more about Refrigeration Technologies HERE. If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Bryan talks about the differences between mineral oil (MO) and POE oil, the advantages and disadvantages of using them, and when to use them. Mineral oil (MO) is what we've used for a long time. We like using it because it's very stable; it may have an affinity for moisture, but it is not nearly as hygroscopic as POE oil. Vacuum pump oil is a highly refined mineral oil, and it works so well because it's able to lock in moisture as those non-condensables get sucked out of the system. It is still not much of a solvent compared to POE oil, though. However, the refrigerant may have a hard time carrying mineral oil through the system. So, pipe size, pitch, and trapping are important considerations when you're dealing with mineral oil. POE (polyol ester) oil works much better with newer refrigerants, especially R-410a. These new refrigerants can't carry mineral oil effectively, and so they rely on POE oil, which moves with those refrigerants a lot more easily and doesn't just sit in the evaporator coil. Oil should stay in the compressor, but oil loss will happen over time and should move back to the compressor with the refrigerant. POE oil works with new refrigerants, but it also works with R-22. Overall, POE oil is very miscible, which means that it moves with refrigerant very well. However, POE oil is reactive and acts as a solvent. The POE oil can pick up contaminants a lot more easily than mineral oil, which can wreak havoc on your system. POE oil reacts with moisture to become acidic, which can lead to issues like burnout. (Note: POE oil does NOT react with mineral oil!) Bryan also covers: Refrigerant velocity Oil return Acid scavengers Retrofits   Learn more about Refrigeration Technologies HERE. If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Eric Mele returns to the podcast to discuss quality cleaning and maintenance procedures for small refrigeration systems. These small refrigeration systems include reach-in refrigerators and open-air cases on grocery sales floors. Filthy condenser coils are problems in many HVAC applications, but they're exceptionally nasty in some small refrigeration applications; proximity to food residue (grease, sugar, etc.) makes condensers get dirty quickly. Use plastic-bristle brushes to clean the bulk of the soil on the coil; you may also use shop vac extensions or even pull out coil cleaner in some cases. If you use coil cleaner, be sure to protect components from the cleaner. When doing maintenance on a small refrigeration system, try to prepare for the cleaning ahead of time. Drain cleaning and maintenance on small refrigeration systems is quite similar to other commercial systems. Drain backups are also a major cause of callbacks. It would also be wise to check that your drain pan heaters are working. You may have to use hot water in low-temp applications, as moisture may freeze on the coil. If you can't use hot water, you may consider using blower fans to avoid freezing (or just letting the unit defrost if you can). Different climate zones have unique issues. For example, in Florida, we tend to have issues with voltage from the utility companies and constant heat. So, we need to test capacitors because they fail quite often. Overall, the philosophy of good maintenance is to "do no harm." Astute observation skills are also very helpful when you do maintenance, as you'll be checking many components. Eric and Bryan also discuss: Ambient temperature ratings Radiant heat in grocery settings Using compressed nitrogen for cleaning Food prep areas "Dry" steam cleaning What if the box is not meeting temp? Cutting bleed resistors Unnecessary maintenance procedures   If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Bryan talks about the top refrigerant leak detectors, the best refrigerant leak detection practices, and some good leak detection tips. Leak detectors require some flow through them. Otherwise, they won't detect leaks. So, these tools have small pumps inside of them to move air through them for sampling. Leak detectors also require some time to warm up, so keep that in mind when you approach a job. One type of leak detector is a heated diode (sometimes called a heated pentode). It is a heated electronic leak detector that takes a sample and analyzes it within. Infrared detectors also exist, but they require you to move the tool consistently; these tools constantly recalibrate themselves, so you can't hold it still while you're using it to locate a leak. Once you confirm that you have flow, you need to determine that the detector is actually working. Make sure that your detector can pick up tiny leaks, not just large ones from cracking open a can of R-410a. So, we recommend using leak references that you can use to test your detector. One of those references is a leak test vial. Some leak detectors have a tip filter, which prevents contaminants from getting into the system. Make sure that your detector has a filter and that you change it regularly. You don't want water or other contaminants getting into your leak detector and breaking it. Another surprising contaminant is leak bubbles; these bubbles can also set off a leak detector, so be careful to manage your order of operations to avoid false positives. These tools work best if you store them in clean, dry places. It is also a good idea to keep a backup in case your main leak detector breaks or loses accuracy.   Learn more about Refrigeration Technologies HERE. If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone subscribe HERE.

How does a vacuum pump work? When should you change the oil? What does that oil do anyway? Kevan Mayer of NAVAC comes on the podcast to answer these questions and more in this episode. Vacuum pumps help remove moisture and non-condensables from the system. Moisture can freeze at temperature drops in the system, and it can block refrigerant flow to the system. Moisture can also combine with POE oil to become acidic, which causes burnouts. A vacuum pump uses an impeller to bring a system under negative pressure. Many of these pumps are two-stage pumps, meaning that they have multiple chambers that push the contaminants through the pump before they get discharged into the atmosphere. As with other tools, it is a good idea to confirm your vacuum pump's operation regularly to make sure you can use it effectively. Vacuum pump oil is a type of highly refined mineral oil and should be clear. It is hygroscopic and attracts moisture, like POE oil, so you need to take care to avoid contamination. This oil both lubricates the vacuum pump and absorbs incoming moisture from the system. It's a good idea to replace your vacuum pump oil every job when you have a small pump; you may even need to change it multiple times per job. Larger pumps will typically handle a few jobs before you need to change the oil. In any case, change the oil if it starts looking amber or milky. Kevan and Bryan also discuss: Gas ballast valves Vacuum gauges and micron gauges Changing gaskets in hoses Proper oil disposal Vacuum pump size Vacuum pumps with solenoids NAVAC pumps and features Dedicated vacuum hoses Standing vacuum tests   Check out NAVAC at navacglobal.com, or look for their products at trutechtools.com. Learn more about Refrigeration Technologies HERE. If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

In today's short podcast episode, Bryan covers some tips about HVAC/R service valves and caps for new technicians. While service valves may seem simple, there are some things you should know about them before you handle them in the field. Before you connect your gauges, ask yourself if you even need to connect gauges. If you've already benchmarked the system and know what to expect, then you may be able to suffice with line temperatures. If you have a system with caps or Schrader cores and need to hook up your gauges, be careful not to cover any leaks in the cap or Schrader. You could potentially miss a leak on a cap or Schrader, so be sure to inspect those before you hook up your gauges. Service valves require gentleness and care when you take caps off and on. You don't need to overtighten caps and Schraders, as they mostly come together at an O-ring fitting or with a flare; check to make sure that you're using the correct caps and that those caps have their proper seals, if applicable. If you need to use a thread sealant, a dab of Nylog comes in handy. If you're too hard on it with a wrench, you could break the entire service valve. When you braze in or around a service valve, you'll want to protect it from heat. One of the best ways to do that is to tie a wet rag around it or use Refrigeration Technologies WetRag heat-blocking putty. (Remember, leave the Schraders out while brazing!) Overall, you'll really need to think about protecting that service valve from damage any time you work on it.   Learn more about Refrigeration Technologies HERE. If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Jamie Kitchen returns to the podcast and talks all about hard shut off TXVs/TEVs. He discusses bleed and non-bleed valves and why the TXV type matters to your compressor. When it comes to TXVs, there are two main types: bleed and non-bleed. The former may be referred to as a bleed TXV, and the latter may simply be called a TXV. However, OEMs may refer to TXVs as a "hard shut off TXV" (HSO), which is a non-bleed TXV. The core difference between bleed and non-bleed TXVs is the equalization speed. That equalization speed affects how your compressor runs; equalizing the system reduces the pressure differential that the compressor will have to overcome on startup. Non-bleed/hard shut off TXVs may cause the compressor to draw locked rotor amps because the pressures did not equalize. To mitigate that issue, you can put in a start cap and relay on the compressor or replace the valve with a bleed TXV. The main purpose of hard shut off TXVs is to prevent refrigerant migration and flooded starts when the system is off. The non-bleed TXV does not permit equalization, which builds pressure and but keeps refrigerant in the condenser, not the evaporator. Although the compressor will have to overcome more pressure upon startup, it will be less likely to fail due to a flooded start. However, some manufacturers may recommend using a hard start kit to overcome that pressure if you use a hard shut off TXV (even on scroll compressors!). Jamie and Bryan also discuss: Non-bleed TXVs on scroll compressors Pressure rising and falling throughout the system Opening/closing forces Superheat spring Liquid refrigerant migration Shutting off the suction line vs. using a liquid line solenoid valve Proper equipment sizing and short-cycling Charging with bleed vs. non-bleed TXVs Energy benefits   Learn more about Refrigeration Technologies HERE. If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

In today's podcast, we cover why both compressor and evaporator superheat matter. We also address some common confusion related to each. Evaporator and compressor superheat are two different readings that give you different indicators about the system's health. When you look at evaporator superheat, you see how far you feed boiling refrigerant into the evaporator coil. You don't want to overfeed your evaporator coil and risk flooding your compressor. However, you also don't want to starve your unit and reduce suction pressure. You'll want to stay between 5 and 14 degrees (F) of superheat at the evaporator outlet on typical A/C systems. On TXV systems, we can control superheat at the evaporator outlet. Evaporator superheat is the reading that helps you optimize your capacity. Increasing it will decrease your evaporator capacity, as the evaporator coil won't be fed as much refrigerant. The lowest possible value is your best bet for maximizing efficiency and capacity. Compressor superheat can be measured before the compressor. When you know that value, you can predict how hot your compressor will be when it runs. The temperature can increase from the evaporator outlet to the compressor inlet. Poor insulation in close proximity to the liquid line can be a cause; heat can transfer from the warm liquid line to the cool suction line. Our goal is to minimize heat gain in the suction line, so we want to insulate our suction lines and keep them as short as possible. However, you don't want the compressor superheat to be so low that you end up flooding the compressor. In most cases, you should check both values to evaluate the heat gains or losses in your suction line.   Learn more about Refrigeration Technologies HERE. If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

In today's podcast, Jim Bergmann joins us to talk about evacuation. He discusses pulling a vacuum, conductance speed, microns, core removal, decay rate, and all that other nerdy vacuum stuff. Jim has helped develop some new BluVac hoses with AccuTools, and he's here to explain why we need those. He also explains why we need to be more educated on evacuation. While we have many good hoses today, we still have a way to go when it comes to moisture removal. Jim Bergmann has seen the need for more durable hoses that perform better when there's moisture and acids in the system. Pulling a vacuum that makes the system dry is crucial for that equipment's longevity. You cannot over-vacuum a system, so the deeper vacuum you can make, the better your evacuation will be. Evacuation often takes place on new pieces of equipment, and some people worry that deep vacuums will compromise the oil quality of those new systems. That is actually not a real issue to worry about during evacuation, and it's a piece of misinformation that makes people misunderstand the importance of evacuation. Not enough people understand how evacuation works, and that is how misinformation and distrust around evacuation spread throughout the HVAC industry. Evacuation best practices come down to the materials you use. We'd like to use a dedicated evacuation rig with the highest possible conductance speed. So, to achieve that, you'll want as few fittings/connections as possible and wide, short, high-quality hoses that are impermeable and leak-free. Remember to remove all Schrader cores and use your micron gauge away from the pump. Pull the vacuum down as deep as you can get it and do a decay test. Bryan and Jim also discuss: Degassing and dehydration Best evacuation technologies of yesterday and today Evacuation education gap TruBlu hoses Pressure, density, and air "thickness" Moisture adhesion Behavior of water Hose ratings POE oil and moisture   Learn more about Refrigeration Technologies HERE. If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

In today's short podcast episode, Jim Bergmann and Bryan answer the age-old question: Can you really freeze water in a vacuum by pulling down too fast? Is that a problem? What should you do about it? Here is the short answer: NO. You CAN'T freeze water in a vacuum in a typical residential A/C system. First of all, you would need to have water in the system to freeze water in the system. We typically don't see large amounts of water in JVAC systems, but there could be moisture in the evaporator coil in refrigeration. Coupled with the very low temperatures, you could see freezing under vacuum in those systems. However, you will almost never see freezing moisture under vacuum in residential comfort cooling. On top of that, you would need to have enough water to freeze, not even considering the vacuum speed. We cannot achieve a vacuum that would cause that much water to freeze in a system. When you perform a decay test, the pressure rise will taper. (If it doesn't rise, then you have a leak.) When the pressure tails off, you've likely come across moisture in the system. You can usually remove that moisture without having to worry about freezing; that moisture will merely exit the system under vacuum, and it typically will not freeze. But what about water in a normal, non-HVAC vacuum? Can you freeze water in a vacuum then? YES. The water would vaporize before it freezes, and it would sublimate off very quickly on most vacuum rigs. You can check out this article and video to watch an experiment in action.   Learn more about Refrigeration Technologies HERE. If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.