Month: March 2018

This article was written by Senior Refrigeration Tech Jeremy Smith. Before we get to it I want to remind you that ALL of the tech tips are available in alphabetical order HERE – it’s a great link to share with other techs, HVAC business owners, Trade school students etc… you can feel free to share these anywhere.


Alright, maybe “advanced” isn’t the right thing to call this little tidbit, maybe it should be “troubleshooting and information sharing in the digital age….”

Microprocessor controls, PCBS, PLCs, call them what you will, electronic circuit boards have become an integral part of the HVAC/R world. From a small heat pump defrost board to an advanced building automation system, these little pieces of equipment seem to be the bane of a techs existence.

One very important thing to remember when working on a system with one of these items installed is that each one has a specific troubleshooting procedure and its own sequence of operations.

So, how is a tech supposed to remember all of this stuff?

Pro Tip.

You DON’T.

Chances are good that you’re reading this on a smartphone or a tablet. With that and a couple of free apps, you can build a library of tech manuals, reference documents and other information to allow you to be better at diagnosing problems on specific equipment.

 

So, how do we build this? Well, you can go Old School and print out all of the manuals and store them in your service truck, or we can keep up with the times and go HVAC/R School and put it in “The Cloud”.

 

Everybody has a Gmail account. Maybe it’s your primary email, maybe it’s the one you give people that you don’t really like so you never hear from them again. Well, with every Gmail.

account comes 15GB of free online storage through an app called Google Drive. Grab the Google Drive app from the app store or play store and, if your Gmail is logged in to that phone, the drive app is already logged in to access your cloud storage. Now, start to “build” your reference library by uploading those PDF files to the drive.

Sometimes this is easier to do on a PC, but it can be done from a phone or tablet as well, it’s just a bit more tedious, at least for me. Then, the next time you’re on a job and have to search and find a manual for a piece of equipment you’re working on, save it to your Google Drive, too. Before long, you’ll have a very
nice library to draw from.

If you’re feeling particularly generous, within Google Drive, you can share that information with co-workers and other techs. You can either allow them to contribute to the library or just to view
it.

You know what’s better than having a good memory? having good resources. Oh and reading… you pretty much can’t be a good tech nowadays if you never read.

Sorry…

— Jeremy

Here is another great explanation from Michael Housh from Housh Home Energy in Ohio.Thanks Michael!


I’m going to layout and compare the Sensible Heat Rate equations for both the air-side and water-side of HVAC, to help draw similarities and dive deeper into the science behind these equations.  This is the beginning of a series to try and help us all gain a deeper knowledge of where these equations come from. The more we learn about the two, the more similarities can be drawn between them. This will hopefully allow a technician to be more comfortable when faced with different systems in the field.  I should also note that while the equations can be complex, they are a great reference for those who would like to build them into spreadsheets (or other formats).

 

Sensible Heat Rate Equations:

 

Air

Water
Q = 1.08 * CFM * TQ = 500 * GPM * T
Where:Where:
Q = sensible heat transferred (Btu/hr)Q = sensible heat transferred (Btu/hr)
CFM = quantity of air (ft3/min)GPM = quantity of water (gallons/min)
T= dry bulb temperature difference (°F)T= dry bulb temperature difference (°F)

 

The only thing I will say about the Delta-T side is that it is the measurement of dry-bulb temperature, this is something I think all technicians know and have a decent grasp on.

 

Like most things in our industry these are “rules of thumb” equations, however, both derive from the same lower level equation, which is as follows:

 

Q = M * C * T

 

Where:

Q = sensible heat transferred (Btu/hr)

M = mass of the fluid (lb/ft3)

C = specific heat of the fluid (Btu/lb)

T= dry bulb temperature difference (°F)

 

I’ve often heard Bryan say that air-conditioning is about moving pounds of refrigerant.   We move pounds of refrigerant to create air-conditioning, and we move pounds of air to deliver that air-conditioning to the space.  As you may have gathered from the above equation the Sensible Heat Rate is derived from moving pounds of a substance (in our case air or water).

 

I’m not going to dive into the details of the above equation at this time, but wanted to share where both of these equations stem from. What I’d like to breakdown in this article is a deeper understanding of where the 1.08 (air) and 500 (water) constants come from.   Both CFM and GPM are actually what provides the “pounds” of the fluid (air is a fluid), based on density and specific heat.

 

Density is defined as its mass per unit of volume (or weight per unit of volume), and specific heat is the rate at which an object will give off or absorb thermal energy.  Both density and specific heat are moving targets, but in the “rule of thumb” below are the values that are used.

 

Density (lb/ft3)Specific Heat (Btu/lb)
Air @ 70°F & at sea-level (14.7 psia)0.0750.24
Water @ 60°F62.371.0

 

I’m going to solve for the water-side first.  We have to take into account that our measurement for water is Gallons Per Minute, so for anyone who doesn’t know, there are approximately 7.48 gallons in 1 cubic foot.  Using the density from the table above we can solve for the weight of one gallon of water 62.37 / 7.48 = 8.34 lb @ 60°F.  Since our end result of the Sensible Heat Rate equation is Btu/hour we have to convert our GPM -> GPH (gallons per hour).  So, our 500 is a simplification of the following values:

 

Constant = 8.34 (lbs/gal) * 60 (min) * 1 (specific heat) = 500

 

When we provide the GPM in the Sensible Heat Rate equation for water, we have already accounted for its density (mass), specific heat, and converted to gallons per hour.

 

Next, let’s look at the air-side.  Here we have to account (just like in the water-side), that our measurement is in Cubic Feet per Minute, and since we are solving for Btu/hour we will have to convert CFM – > CFH (cubic feet per hour), we also have to use the density to account for the mass of air that we are moving, and the specific heat.  So, our 1.08 is a simplification of the following values:

 

Constant = .075 (density [ lbs/ft3]) * 60 (min) * 0.24 (specific heat) = 1.08

 

So, just like the water side, when we provide CFM to the Sensible Heat Rate equation, we have already accounted for its density (mass), specific heat, and converted to cubic feet per hour.

 

I hope I haven’t utterly confused you on such a technical topic, but stay tuned for more in the series to help bring the Sensible Heat Rate equation (and the air / water side) closer together.

— Michael Housh

This tip is written by 19 year service tech Frank Mashione. Thanks Frank.

Here is a tech tip from the field that had stumped me. Lucky I knew the right person to call to get back on track.

This business has complained about heat calls for quit a while. I have heard other techs mention it in passing. I ran into our installation crew there about a month ago on a different job. Yesterday was my turn to take a crack at it.

They had called a different company day before and they said it was working fine. When I arrived checked thermostat set at 73 and 65 in store, so I checked another thermostat set at 73 and 70 in the store.

I Got up on the roof found both units locked out on high limit, which is 4 blinks for these Trane gas packs. I found it odd that the units were locked out on high temperature but the indoor fan was not running or inducer. I cycled power and the unit restarted. Next I checked gas pressure, it was on the high end of manufacturers specs so I adjusted it back just a bit.

In the back of my mind, I thought I had it. I checked static pressure found it at 0.6″ wc which isn’t too bad especially for the area I work in which I regularly see static off the charts.

The temperature rise was 55° which was acceptable but the return temperature was reading high. I put my wireless air probe in the location of the high limit. After some run time, the temperature in the high limit was approaching the trip point of the limit. This made it clear that the limit was doing its job by tripping.

The unit would run about ten minutes then trip on limit. After four trips it would lock out for an hour.

This got me looking again at the return temperature and I realized that it was much higher than the indoor temp.

The cause of the problem was the supply was installed too close to the return making return temperature high tripping out high limit. After nineteen years in the business still finding new things to learn.

Frank Mashione service technician

In HVAC/R we are in the business of moving BTUs of heat and we move these BTUs on the back of pounds of refrigerant. The more pounds we move the more BTUs we move.

In a single stage HVAC/R compressor, the compression chamber maintains the same volume no matter the compression ratio. What changes is the # of pounds of refrigerant being moved with every stroke(reciprocating), oscillation (scroll), or rotation (screw, rotary) of the compressor. If the compressor is functioning properly the higher the compression ratio the fewer pounds of refrigerant is being moved and the lower the compression ratio the more pounds are moved.

In A/C and refrigeration the compression ratio is simply the absolute discharge pressure leaving the compressor divided by the absolute suction pressure entering the compressor.

Absolute pressure is just gauge pressure + atmospheric pressure. In general, we would just add the atmospheric pressure at sea level (14.7 psi) to both the suction and discharge pressure and then divide the discharge pressure by the suction. For example, a common compression ratio on an R22 system might look like-

240 PSIG Discharge + 14.7 PSIA = 254.7
75 PSIG Suction + 14.7 = 89.7 PSIA
254.7 PSIA Discharge ÷ 89.7 PSIA Suction = 2.84:1 Compression Ratio

The compression ratio will change as the evaporator load and the condensing temperature change but in general, under near design conditions, you will see the following compression ratios on properly functioning equipment depending on the efficiency and conditions of the exact system.

In air conditioning applications compression ratios of 2.3:1 to 3.5:1 are common with ratios below 3:1 and above 2:1 as the standard for modern high-efficiency Air conditioning equipment.

In a 404a medium temp refrigeration (cooler) 3.0:1 – 5.5:1  is a common ratio range

In a typical 404a 0°F to -10°F freezer application 6.0:1 – 13.0:1 is a common ratio range

As equipment gets more and more efficient, manufacturers are designing systems to have lower and lower compression ratios by using larger coils and smaller compressors.

Why does the compression ratio number matter? 

When the compressor itself is functioning properly the lower the compression ratio the more efficient and cool the compressor will operate, so the goal of the manufacturer’s engineer, system designer, service technician and installer should be to maintain the lowest possible compression ratio while still moving the necessary pounds of refrigerant to accomplish the delivered BTU capacity required.

The compression ratio can also be used as a diagnostic tool to analyze whether or not the compressor is providing the proper compression. Very low compression ratios coupled with low amperage and low capacity are often an indication of mechanical compressor issues.

Compression ratio higher than designed = Compressor overheating, oil breakdown, high power consumption, low capacity 

Compression ratio lower than designed = Can be an indication of mechanical failure and poor compression

Understanding compression is critical to understanding the refrigeration process. Don’t be tempted to skip past this because it is a really important concept.

Look at the pressure enthalpy diagram above. Top to bottom (vertical) is the refrigerant pressure scale, high pressure is higher on the chart. Horizontal (left to right) is the heat content scale, the further right the more heat contained in the refrigerant (heat, not necessarily temperature).

Start at point #2 on the chart at the bottom right. This is where the suction gas enters the compressor. As it is compressed it goes to point #3 which is up because it is being compressed (increased in pressure) and toward the right because of the heat of compression (heat energy added in the compression process itself) as well as the heat added when the refrigerant cooled the compressor motor windings.

Once the refrigerant enters the discharge line at point #3 it travels into the condenser and is desuperheated (sensible heat removed). This discharge superheat is equal to the suction superheat + the heat of compression + the heat removed from the motor windings. Once all of the discharge superheat (sensible heat) is removed in the first part of the condenser coil it hits point #4 and begins to condense.

Point #4 is a critical part of the compression ratio equation because the compressor is forced to produce a pressure high enough that the condensing temperature will be above the temperature of the air the condenser is rejecting its heat to. In other words, in a typical straight cool, air cooled air conditioning system the condensing temperature must be higher than the outdoor temperature for the heat to move out of the refrigerant and into the air going over the condenser.

If the outdoor air temperature is high or if the condenser coils are dirty, blades are improperly set or the condenser coils are undersized point #2 (condensing temperature) will be higher on the chart and therefore will put more heat strain on the compressor and will result in lower compressor efficiency and capacity.

As the refrigerant is changed from a liquid vapor mix to fully liquid in the condenser it travels from right back left between points #4 and #5 as heat is removed from the refrigerant into the outside air (on an air cooled system). Once it gets to #5 is is fully liquid and at point #6 it is subcooled below saturation but ABOVE outdoor ambient air temperature. The metering device then creates a pressure drop that is displayed between points #6 and #7. The further the drop, the colder the evaporator coil will be. The design coil temperature is dictated by the requirements of the space being cooled as well as the load on the coil but the LOWER the pressure and temperature of the evaporator the less dense the vapor will be at point #2 when it re-enters the compressor and the higher the compression ratio will need to be to pump it back up to point #3 and #4,

This shows us that the greater the vertical distance between points #2 and #4 the higher the compression ratio, which means that both low suction pressure and/or high head pressure result in higher compression ratios, poor compressor cooling, lower efficiency and lower capacity.

In some cases, there isn’t much that can be done about high compression ratios. When a customer sets their A/C down to 69°F(20.55°C) on a 100°(37.77°C) day they will simply have high compression ratios. When a low temp freezer is functioning on on a very hot day it will run high compression ratios.

But in many cases, you can reduce compression ratios by –

  • Keeping set temperatures at or above design temperatures for the equipment. Don’t be tempted to set that -10°F freezer to -20°F or use that cooler as a freezer
  • Keep condenser coils clean and unrestricted
  • Maintain proper evaporator airflow
  • Install condensers in shaded and well-ventilated areas

Keep an eye on your compression ratios and you may be able to save a compressor from an untimely death.

— Bryan

Proper sizing and orientation of grilles, registers, and diffusers may seem like such a simple thing, but it’s an area where confusion and mistakes are commonly made.

First let’s define some terms.

Return 

A return draws air into a return duct system with negative pressure compared to the space usually via a fixed “grille” but also often called a “return vent” or a “return intake vent” or for some of you old school folks from up north the “cold air return”.

Supply

The supply vents, registers or diffusers blow air into the conditioned area with positive pressure and are responsible for distributing and mixing the air.

Vent

A vent is a generic word for a designed opening or cover that air passes in or out of. When in doubt, just say vent.

Grille

A grille is a fixed vent type that contains no damper or adjustable louvers. Grilles can be used for supply but are most commonly used in return applications. The grille shown above is a steel stamped return grille.

Register 

A register is a vent that contains an internal adjustment damper and often externally adjustable louvers. Registers have the same inlet neck and outlet face size. Air will move straight through registers and grilles.  Registers are the most common type of supply vent.  The register shown above is a common aluminum, adjustable, curved blade, one-way 10×6 ceiling register.

Diffuser 

A diffuser is a vent that has a smaller inlet and a larger face resulting in a lower face velocity than that of the inlet duct. Diffusers often “turn” the air at a steep angle as it exits the face. Diffusers may or may not have adjustable dampers or louvers. The diffuser shown above is a typical tiered, acoustical ceiling 2’x2′ lay-in supply diffuser.

Sidewall Straight Blade vs. Curved Blade Ceiling 

Sidewall registers and grilles have straight louvers to force the air straight into the space with no turning at all at the face. Curved blades direct the flow at an angle and are generally used for ceiling applications.

Sizing

When sizing grille or a register you will measure the OPENING that the grille or register is designed to cover or recess into, not the total external frame size of the grille or register.  The register shown below is a 10×6, sidewall supply register.

Orientation 

Look at the image at the top of the article. This is generally how we describe return grille orientation because return grilles are an instance where grille orientation / louver direction make a big difference.

For return grilles, we state the dimension parallel (running the same direction as) with the louvers first and then the perpendicular dimension second.

For supply diffusers, they are almost oriented with the external louvers parallel with the long dimension on ceiling registers and with the louvers parallel with the short dimension on wall and floor registers like the shown below.

For floor registers, they follow the same rules as return grilles where you state the dimension parallel to the louvers first. This means that floor registers will often be smaller number first like 4×10 or 4×12.

Ceiling and some sidewall registers will usually just be described as long side first such as a 10×6 or 12×8 but that can vary from brand to brand.

Yes, it is pretty simple, but also essential for clear communication.

— Bryan

P.S. – This episode of the podcast with Jack Rise covers common duct and vent mistakes that you may want to know.

We’ve all been new at one time or another so there is no need to get all judgy about some of the mistakes new techs make just because they are inexperienced.

However…..

These are some very preventable mistakes that occur due to simple oversight and carelessness that need to happen 0% of the time.

Caps and Seals

Leaving caps off is never OK. While it’s true that Schrader valves and back seating service valves “should” seal completely and shouldn’t be left leaking it is always possible that a little leakage can happen. Besides, keeping bugs and dirt out of the ports is reason enough to keep the caps on.

Bill Johnson (co-author of RACT) made a really good point on a recent podcast. When a system is apparently low (which you can verify through non-invasive temperature tests) you shouldn’t just pull off the caps and attach the gauges. First, look for oil at the ports and leak check them to eliminate port leaks as a possible cause. Once you remove the caps and attach your manifold you won’t be able to know if the ports were a leak point or not.

Every time I remove caps I look inside them to make sure they are in place unless it is a flare hex cap that doesn’t require a seal.

It’s a good practice to keep all caps and screws together and in the same place on every call. This helps to ensure they don’t get accidentally knocked into the dirt, lost or forgotten.  Put those caps back on, finger tight for caps with seals and snugged up with a wrench for hex flare caps (Trane residential units for example).

Leaving Disconnects Out / Off

Obviously, nobody TRIES to forget the disconnect but it still happens all the time and it’s almost always because the tech gets in a hurry or distracted and usually both, and it can be eliminated easily by some best practices.

Most often the disconnect is left off or out during maintenance or during very simple repairs. This is because the tech will often run test the equipment, then perform the maintenance or minor repair and leave without run testing again. This order of test first then clean / repair isn’t my favorite for several reasons will silly mistakes being one of them.

I advocate for performing the comprehensive run test at the very end of a repair or maintenance meaning you are observing the system running right before you leave with the last action being resetting the thermostat or controls back to the desired setpoint. When you run test last you don’t forget silly things that prevent the system from running.

Always do a final walk of the job before leaving and check disconnects, setpoints, cleanup and check for tools.

Making Poor Electrical Connections 

I see it all the time. Capacitors tested and the spade connections left loose, contactor lugs not properly torqued, stranded wires with some of the strands cut off to make the wire fit, crimp connections on solid wire…. the list goes on and on. Here are the top mistakes to avoid.

  • When forcing on a female spade (on a capacitor for example) it should be very snug. If it is loose at all, pull it off and pinch down the spade sides a bit to ensure it’s a snug fit
  • When making a crimp connection only do so on a stranded wire and use an appropriately sized connector. Position the jaws so that the indent crimp is made on the side of the connector OPPOSITE the split in the barrel. Even better is to use a crimper specifically designed for insulated terminals that compresses the entire barrel.
  • Never cut strands of wire to make a conductor fit under a lug. Use the proper connection (termination) type for the conductor.
  • Never leave exposed wire, strip back insulation only to the length required to make the connection and no more.
  • Don’t leave connections under tension. Use straps and zip ties to keep tension away from connections so that they aren’t left under a pulling/disconnecting force.
  • Make appropriate connections for the job, never leave connections open to the environment unless they are rated for it.

When making any electrical connection always pull the connection to make sure it is a snug fit before walking away.

Failing to See the Obvious 

So much is made of good workmanship (how things look) and diagnosis (figuring out what’s wrong) and rightfully so. However, for a new tech, nobody expects you to do the best looking work out there or to diagnosis the super difficult situation. You are expected to use common sense and spot things that are out of the ordinary or that can lead to issues. Here is a quick list of things to look out for that you can see with little to no experience.

  • Look for refrigerant oil stains, often oil stains or residue can lead you straight a refrigerant leak.
  • Use a mirror and a flashlight and look for dirty evaporator coils and blower wheels. You may make a diagnosis but if you leave the system with a dirty coil or a blower wheel you still look silly.
  • Check the air filter and let the customer know you checked it. A home or business owner may not know much about HVAC but they know what an air filter is and reporting the condition back helps give them confidence.
  • Watch for rub outs on copper lines, feeder tubes, external equalizers and sensing bulbs and wires. You can often find or prevent a problem just by looking for areas of contact between tubes and/or wires.
  • Inspect control wiring for cuts or UV damage outside. If the weedwhacker doesn’t get the wire often the sun will.
  • Look for past workmanship that may be done incorrectly. Just because that fan motor or capacitor is new doesn’t mean it is the right size and wired properly. Always double check your own work as well as work done by others.
  • Before making a repair double check the previous diagnosis and check that the part you have is actually the correct part. There is NOTHING worse than removing a compressor t find out the one you have isn’t the correct one. ALWAYS double check the diagnosis and the part.

There are many other things that could be added to the list, but for a new tech if you do the following you will be on the road to success even if you are green.

  • Read product manuals and never stop learning
  • Listen carefully to senior techs and ask lots of questions
  • Help other techs when they are in a pinch
  • Smile and treat customers with respect
  • Compete with yourself to do each job better than the last
  • Walk  every job before you leave to make sure everything is buttoned up (Screws, caps, disconnects)
  • Ask every customer is you have done everything to their satisfaction and if there is anything you can improve.
  • Do all the little things with exceptional detail. Cleaning drains, washing condensers etc… always do it with a level of detail that exceeds your peers and you will build a reputation for excellence.

If you do these things your co-workers, customers, and managers will generally overlook the mistakes you make just because you are green.

— Bryan

Michael Housh from Housh Home Energy in Ohio wrote this tip to help techs determine the air side charge on a pressure tank. Thanks, Michael!


Determining the air-side charge of an expansion tank in a hydronic heating system is a relatively easy task.  A properly sized and charged tank is designed to keep the system pressure about 5.0 psi lower than the pressure relief while the system is at maximum operating temperature.

 

The proper air-side charge is equal to the static pressure of the fluid at the inlet of the tank plus an additional 5.0 psi allowance for the pressure in the top of the system.  The air-side of the tank should be checked and adjusted before adding water to the system, if the tank is already installed and the system has pressure in it, the pressure should be drained at the tank to 0 psi before testing the pressure on the tank.

 

The formula for calculating the air-side pressure is relatively easy and directly related to the highest point in the system from the inlet of the expansion tank.

 

Pa = H * (Dc / 144) + 5

Where:

Pa = air-side pressure in the expansion tank (psi)

H = height from the inlet of the tank to the highest point in the system (ft)

Dc = density of water at its coldest state / typically filling (lb/ft3)

 

The above graph shows us the relationship between density of water and temperature between 50°F – 250°F.

 

A lot of the “rule of thumb” equations for hydronic systems are based on the density of water @ 60°F is 62.37, so we could simplify the above equation into a rule of thumb equation by first solving for the density (Dc).

 

Dc = 62.37 / 144 =0.433

 

Substituting ‘Dc’ into the original equation would give us a slightly less complicated equation that can be used as a rule of thumb to solve for the air-side pressure.

 

Pa = H * 0.433 + 5

 

Below is a graph that shows us this rule of thumb equation and the required air-side pressure based on the height of the system piping.

— Michel H.

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