HVAC School - For Techs, By Techs

Latest Episodes:

Prevent Compressor Murder Part 1 w/ Emerson Apr 17, 2018

Show notes

In today's podcast, we talk with Trevor Matthews with Emerson. He tells us about the causes and prevention of air conditioning and refrigeration compressor failure.

Most compressors don't die a natural death... they're murdered. Of course, that's to say that installation and maintenance play a major role in the compressor's operation and lifespan. Electrical and mechanical failures are the two broad causes of compressor failure.

When it comes to electrical failures, Trevor often sees single-phase compressors fail early when their electrical components don't receive proper inspections and care. For example, contactors may go too long without inspection or replacement. Three-phase compressors are also prone to phasing issues and may run backward.

Common mechanical failures deal with oil in the system. Oil lubricates the bearings inside the compressor. Unfortunately, that oil can mix with liquid refrigerant, become diluted, or experience acid contamination. Some oil-related failures include floodback, flooded starts, slugging, overheating, oil loss, and contamination. Compressors cannot compress liquids, so many of them fail when the refrigerant condenses to a liquid inside the compressor.

Many failures occur because technicians don't think they have enough time to troubleshoot or inspect the whole system. Trevor recommends setting up a checklist with all of the tests you need to perform.

Trevor also discusses:

Service replacement compressors vs. OEM compressors
Megohmmeter usage
Causes of floodback/flooded starts
Compressor superheat
Suction accumulators
Bearing wear
Temperature control and pump cycles for controlling flooded starts

Verifying System Operation Sheet from Emerson http://hvacrschool.com/CompFailures

Intro to Manual J & S w/ Jack Rise Apr 12, 2018

Show notes

In today's podcast episode, we talk with system and duct design educator Jack Rise about ACCA Manual J load calculation and Manual S system selection.

Many people know about Manual J, but relatively few techs follow it properly. When people attempt to do Manual J calculations, many of them go wrong when they overestimate the difficulty of the equations in Manual J. However, many of these techs do better when they can use software like Wrightsoft to help with their load calculations. The best way to approach load calculations is to develop confidence in software programs and field experience (sizing equipment and sealing ductwork); you are more likely to make mistakes if you put all of your confidence in one or the other. Some techs also don't take the time to measure buildings properly if they are either over-reliant on technology or too confident in their field skills.

Manual S is all about equipment selection after the load calculation. However, much of the manual is not useful for fieldwork. The rules are also not as regionally thoughtful as they could be, especially regarding furnace sizing and the consequential heat loss. Manual S is only useful if you perform a Manual J calculation first and use that result as a guide. Rise does not believe that Manual S is bad, but he thinks it gives installers way too much leeway on sizing as it stands.

Jack and Bryan also discuss:

Wrightsoft
Manual J practices in different types of buildings
Envelope leakage in retrofit applications
Most important chapters of Manual S
Accounting for sensible and latent heat load
New ventilation requirements
Odors, cooking, and building design
Increasing airtightness in building construction
Encapsulated attics

Learn more about ACCA standards and codes at acca.org.

Learn more about Wrightsoft HERE.

If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Low Voltage Diagnosis Basics w/ Bill Johnson Apr 03, 2018

Show notes

In this podcast, Bill Johnson shares his practical tips to make low-voltage electrical diagnosis easier in HVAC work. Bill is one of the original authors of the Refrigeration and Air Conditioning Technology manual.

A common issue that techs have in low-voltage diagnosis is that they overcomplicate the issue. Techs should take the time to trace out the system and see where all the wires lead. The techs can be more effective if they know a system's components and those parts' relationships. During diagnosis, some techs also don't allow themselves to use their hands. Bill recommends using an alligator clip on the system as you "walk your way" through the whole circuit for diagnosis.

"Short" is a commonly used term. A true "short" occurs when the current takes an undesigned path with almost no resistance. Some of the things that we casually call "shorts" are actually open-circuit issues where the current doesn't make it all the way through the circuit. Real "shorts" include shunts on the load and blown fuses. If a fuse blows but everything else in the low-voltage circuit seems to be operating fine, check the amperage at the transformer outlet.

Electronic boards give techs a lot of trouble because they seem complicated. But, in the end, these boards are just switches where a hot wire goes in and a hot wire goes out. (The common wire goes straight through the board.) The board is nothing more than a distributor of voltage, and the best way to work on them is to simplify them. You can simplify electrical boards by figuring out the inputs, outputs, and sequence of operation.

Bill also discusses:

Grounding on one leg
Connecting to ground
"Probing" the hot side
Measuring amperage on a thermostat
"Spark-tricians"
Commercial vs. residential low-voltage electronics
Stripping wires

If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Introduction to Walk-in Refrigeration Mar 28, 2018

Show notes

In this podcast episode, refrigeration tech Eric Mele talks us through some common characteristics of walk-in freezers and refrigerators. Eric recently discussed reach-in refrigerators on the podcast, and you can listen to him talk about those HERE.

Common walk-in applications include coolers, freezers, and wine rooms. You may even see some package units. Condensers typically go on top of the box or the roof, and evaporators are inside the refrigerators. Many of these refrigerators also have pump down solenoids on their equipment. Thermostats mostly control the opening or closing of the solenoid valve. To cycle the unit, you shut off the liquid line and let the system pump all the refrigerant into the condenser.

Evaporators tend to come in the side-discharge or pancake-style varieties. Wine rooms may also have ducted evaporators. Some older evaporators may not have fans; we call these gravity evaporators.

Heaters are components that you'll see quite often on walk-in equipment. Drain pan and drain line heaters are critical for walk-in coolers, especially freezers. You can test them by touch or by using a thermal imaging camera. Freezers also have door heaters. Walk-ins also have low-ambient controls. Fan cycling is a low-ambient strategy, but commercial walk-in refrigerators may also have a headmaster.

When you first start working on walk-ins, you may feel overwhelmed if you don't have all the parts on you. However, if a unit has multiple fans and only one is not working, you can typically still run the equipment if you cover the faulty fan and seal up the opening in the shroud. The goal is to get (or keep) the equipment running to save consumable products.

Eric and Bryan also discuss:

Pressure switches
Defrost controls
Troubleshooting equipment (sight glasses, etc.)
Adjusting charge
Superheat values
Patching coils

If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Short #5 - Wire Routing & Connection Mar 27, 2018

Show notes

In this short podcast episode, Bryan covers some basic best practices for wire routing and wire connections in HVAC work.

When it comes to electrical work of any kind, the wires must have proper protection. For example, the wires must be in the proper conduits. They must also work on appliances that they are rated for. HVAC technicians must also understand their qualifications against local codes to ensure they have been authorized for electrical work.

You also NEVER want to route the wire through an opening you can't shove your finger through. If you can cut your finger on an opening, then that opening will probably cut the wire. If you need to run a wire through one of those difficult places, use a grommet. In any case, make sure you properly strap the wire, such as with zip ties. Do NOT trim wires to make them fit a connection.

When routing wire, you WILL be making connections inside the appliance. Make sure you know your connectors and their ratings to make the best, safest connections possible. Check if there is any tension at the connections and disconnects; if there is tension AGAINST the terminal, check your wire angles and adjust them until they sit still or have a little tension towards the terminal. The goal of creating a good connection is to avoid melting, arcing, and other unsafe conditions. Replace melted plugs and leads entirely if you come across them.

When you make a crimp connection, make sure you give them a good tug to check their tightness. Make sure there are no exposed wires by your crimp connections. Soldered connections are usually excellent connections, especially with heat shrink over them.

Bryan also discusses:

Using torque screwdrivers
Terminal crimping (insulated terminals, indentations, using ratcheting crimpers)
Lineman splice
"Doubling over"

If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Furnace Commissioning Part 2 w/ Jim Bergmann Mar 21, 2018

Show notes

In the second part of this podcast series, Jim covers the basics of furnace commissioning in more detail with some common-sense practices. (Listen to Part 1 HERE.) Even though installers set up a furnace system, the technicians help with the equipment startup and commissioning. That way, two parties can ensure that the installation is proper.

The technician is perhaps better equipped to check the electrical connections. As technicians, we can also check the polarity of the power supplies (ensuring that the sine waves are in sync). If the polarity is backward, sometimes the hot wire has been switched with another wire, or you may have to switch the primary or secondary on the transformer. Flame rectification also ties directly into the electric components of a furnace.

Inspection is also a critical component of furnace commissioning. As such, our eyes and ears will be our most important tools during the commissioning process. During the inspection, we should check over the original factory parts to ensure that everything is in order and that the furnace will operate safely.

After we've calculated the temperature rise and set the blower speed, we must evaluate our static pressures. The static pressures let us know how our motors and ductwork are doing. The goal is to get our static pressures as close to 0.5" wc as possible.

Be sure to perform a flame disruption test to ensure that the flame does not starve. Many technicians also fail to check the high limit cutout. When techs fail to check that cutout, the heat exchangers can break from stress. To check that high limit cutout, we can use a piece of cardboard to block the filter; that blockage raises the temperature, and it's our job to make sure that the limit cuts out and shuts the burners down.

Jim also discusses:

Grounding screws
ECM motors
Home insulation and furnace/ductwork sizing
Furnace switches/safeties
Flame rod microamps

If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Short #4 - Blower Taps Mar 19, 2018

Show notes

In this short podcast episode, Bryan talks about blower taps in furnace systems. He explains how to set up their fan speeds and repair them.

Before you even look at the blower taps in a system, you must know a bit about the system design. Is the system supposed to remove high amounts of sensible heat? What is the capacity? How quickly should the thermostat drop? When a system is supposed to move lots of heat and has a high capacity, it needs high airflow; to run optimally, the system needs higher fan speeds to move more CFM per BTU. Moreover, a Manual J calculation can tell you how much sensible and latent heat the system must move. Also, keep in mind that system tonnage does NOT always indicate the amount of BTUs a system is actually moving.

Conversely, to calculate the airflow needed for heating, you must look at temperature rise. Ideally, your temperature rise should be near the middle of the temperature-rise range.

So, how do you set the airflow and know how much you're producing? That's where you measure your static pressure and look at fan tables. Remember to make sure the blower is clean and to factor in additional resistance from components like heat strips or filters. Alternatively, you can measure airflow with a duct traverse or by using an airflow hood. Then, you set the fan speed accordingly.

Overall, to set the blower taps, you need to be able to measure your airflow and read fan charts. If you're merely commissioning a new system, measuring airflow becomes less important; instead, you must ensure that the manufacturer's fan charts are correct. Remember, the airflow needs to be different for a customer's heating and cooling needs.

If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Furnace Commissioning Part 1 w/ Jim Bergmann - Input / Rise Mar 15, 2018

Show notes

In today's podcast episode, Jim Bergmann covers furnace commissioning, including setting up furnace input, clocking the meter, setting temperature rise, and much more. The goal of commissioning is to optimize a furnace's efficiency; we want to make sure we correctly engineer the intake/exhaust system to extract as much heat from the flue gas as possible.

The commissioning process for an 80% furnace is pretty similar to that of a high-efficiency furnace. Checking gas pressure, setting temperature rise, and combustion analysis are critical procedures when commissioning both furnace types. Moreover, you must know the heat content of the fuel and the amount of fuel going into the furnace before you can determine the correct input. There is an acceptable range for gas pressure, typically within 10% of the specs (usually 3.5" wc, so the acceptable range is 3.2-3.8" wc). Both the gas pressure and heat content let you know how efficiently the furnace is firing.

When checking the input, you must clock the gas meter; you do that by timing a single revolution of the gas meter and determine how much fuel goes into the appliance during that time period. You can't have the water heater on at the same time that you are clocking the meter. When you clock the meter, you can start with a gas pressure of 3.5" wc and go up to 3.8" wc. When clocking the gas meter, you may realize that the orifices are incorrectly sized.

Ideally, you want your temperature rise to be in the middle of the manufacturer-specified range. For example, if the range is 40-60 degrees, you would want your temperature rise to be close to 50 degrees).

Jim also discusses:

Weighing condensate
Primary vs. secondary air
Excess air
Changing/resizing orifices
Other gas lines in the home
Ductwork sizing for temperature rise/CFM
Filter considerations

If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Short #3 - Saturation Mar 12, 2018

Show notes

This short podcast episode is about saturation and what it means. Bryan covers related topics, including boiling, evaporation, and condensing.

Saturation refers to something that is "full" of something else. In science, "saturation" refers to a substance being in the middle of a phase change. (For example, boiling water stays at 212 degrees until it all boils off and becomes water vapor.) In HVAC, we often use the term to refer to refrigerant with liquid and vapor are present at the same time. The refrigerant is typically both liquid and vapor in the evaporator and condenser; phase changes occur in those two components as refrigerant changes from a liquid to a vapor and vice versa.

Refrigerant tanks are contained systems, so the liquid-vapor mix remains at equilibrium, and the temperature and pressure will change at a predictable rate. That is why we can use the P-T chart to determine the refrigerant type; a given type of refrigerant that is changing state at a given pressure will always be a certain pressure.

The process of changing state is where we can utilize so many more BTUs of heat. When a substance is at saturation, that substance will not increase in temperature so long as it remains in its current state. However, that substance will continue absorbing heat until it fully changes its state. We call the added heat that does NOT contribute to a temperature change "latent heat." Evaporators are so effective at absorbing BTUs of heat because refrigerants have relatively high latent heat of vaporization values; it takes a lot of added heat to make a refrigerant change from liquid to vapor.

However, evaporation can occur WITHOUT boiling. Temperature is only the average heat content, and some faster-moving liquid molecules can still break free and become gas.

If you have an iPhone subscribe to the podcast HERE and if you have an Android phone subscribe HERE.

Measuring Airflow For Techs Mar 08, 2018

Show notes

In this discussion with Bill Spohn from TruTechtools.com, we cover the practical steps and tools for YOU to start measuring airflow today, if not sooner.

There are several ways to measure airflow; when measuring airflow, start with the "why" rather than the "how." Understand what the goal of the airflow is before you begin taking measurements in random places.

You can take a bulk measurement at a return, but you have to be prudent to avoid human error. The best way to avoid error is to use a TrueFlow grid, which replaces the filter and uses a pitot array to measure airflow in the return. Another relatively easy way to get a bulk measurement is to use a flow hood. However, it can be easy to mess up the positioning of a flow hood (or not have enough room for it).

Many techs misuse tools like vane anemometers and collect poor data. Vane anemometers can gather information throughout the duct (mini vane) or over the supply or return (larger vane). You want to pick up the micro-transitions in air velocity to get quality data; you can use either point or traverse measurements and average those readings to come up with your average CFM.

We can take measurements INSIDE the duct with pitot tubes (although we have our reservations about using those), hot wire anemometers, and mini vane anemometers. In-duct measurements require multiple measurements and consistency during testing.

A common system airflow measurement doesn't measure CFM at all; that measurement would be static pressure. However, you need to have the correct tables and understand all of the load requirements to measure static pressure effectively.

Bill and Bryan also discuss:

Pitot tubes vs. static pressure probes
Air movement metaphors
Point vs. traverse measurements
Static pressure drop
Total system airflow setup
Ventilation airflow

If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

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