This video is the laid-back Ask Us Anything Q&A session from the HVACR Training Symposium. The panel consists of Bryan, Joe Shearer, and Eric Mele. Eric does a lot of commercial HVAC/R work for Kalos Services, and Joe is an HVAC/R contractor in the Tallahassee area.
We had some questions about cleaning line sets. Joe started cleaning line sets with foam pigs instead of just using nitrogen, which can be unreliable. The other widespread option is replacing the copper entirely, which can be a time-consuming task. Foam pigs usually come out in one piece and don't often get stuck, but some of them can have pieces fall off if they run through poorly deburred copper. However, you shouldn't have any problems with foam pieces being left behind in the lines if you purge the lines with nitrogen after cleaning. You can also blow nitrogen through the other side if a pig gets stuck. It's usually best to move the pigs and flush from inside to outside, as the flush may have a chemical odor.
We also had a question about the wear and tear on heat pump inverter compressors that run higher RPM in heat mode in colder climates. Compressors that run at a higher speed and with a higher compression ratio in heat mode will generally experience more wear than those that run at lower speeds with a lower compression ratio. Vapor injection can help keep the compressor a bit cooler, but the compressor will still be in rougher shape than one that doesn't work as hard and run as hot.
Another question dealt with CO2 systems in Florida. Non-cascading CO2 systems are generally not ideal in Florida due to the hot climate. We also can't use adiabatic cooling to keep the CO2 below the critical point because we are in a high-humidity market. However, Eric has been working on a non-cascading CO2 system in Jacksonville, FL, and it will be more likely to work because it will have a cooling tower and water-cooled condensers.
We received questions about whether the TXV sensing bulb location matters. Nowadays, we have modern TXVs that aren't as heavily impacted by sensing bulb location and orientation. The bulb's job is to exert pressure, and it merely needs to be able to pick up the suction line temperature; the contact area is more important than the location. (We also talk about insulating the sensing bulb and have a debate about what's really in a sensing bulb.)
Bert asked about liquid line restrictions, which led to a discussion about hard shutoff (non-bleed) TXVs and how they work. You can identify liquid line restrictions by checking for temperature drops, but you have to be mindful of radiant heat, overcharge, and tool calibration. Bert also asked about Lennox's low compressor fail rates, which could be due to safeties and the use of TXVs instead of pistons.
We also discussed the potential causes of damaged ECMs, including condensate problems, moisture migration, and evaporator coil freezing.
We answered a question about leak rates with the system on or off; refrigerant will leak out of the high side faster when the system is on, and refrigerant will leak out of the low side faster when the system is off. However, pump-down solenoids and other accessories can affect that rule.
Another question dealt with refrigerant oil breaking down when a vacuum is too low. Oil won't fractionate under very low vacuums.
One of the online questions was about how young techs should go about implementing best practices in the face of pushback. A respectful approach generally works best, but we also have to accept that not everybody will want to change.
Someone asked about choosing brands and whether it's okay to vent bath fans into the attic through the ceiling. Nowadays, there's little difference in quality from brand to brand, so value will be one of the main things to consider. However, venting bath fans through the ceiling and into the attic is NOT a best practice.
We also discussed surge protection. Surge protection varies a bit by market, and it depends on the practices of the power company; buck-boost transformers will likely be more effective at managing incoming overvoltage from the power company over the long term.
We received a question about residential monitoring systems and compatible business models. Those technologies can be valuable, but we also need to be realistic about a given company's commitment to maintaining those tools.
Another question dealt with hard starts. Not all systems require hard starts, but hard start kits are often used on compressors that are old and don't require them. However, some manufacturers will require start kits if the compressor requires a temporary increase in current on the start winding (NOT the run winding).
Read all the tech tips, take the quizzes, and find our handy calculators at https://www.hvacrschool.com/.