The Sleeper 

The year was 2002 and I was 20 years old. I had a helper named Clay and he was a really nice guy, probably 15 years my senior, already with streaks of grey in his hair with a way of making you feel at ease… so very at ease.

OK, he was sleeping most of the time…

He fell asleep in my van between most calls and even fell asleep in company meeting leaning against a condenser box.

Now maybe I’m just being judgmental and Clay was a narcoleptic, or maybe he was staying up all night doing superhero work, but I think the guy just liked to grab a few , or MANY winks.

It didn’t really bother me much when Clay would sleep, I could tell he wasn’t learning much and didn’t care much, but he was a pleasant sort of bloke and I didn’t hire or manage him so it really wasn’t my problem.

Nowadays I do employ and train lots of people and now it is my problem and trainees who sleep in vans DRIVE ME CRAZY! Instead of focusing on my evil capitalist anti-sleep, judgy ways right off let’s ease into with some more trainee tales and let’s see if you can catch a thread of commonality.

The Nasty Dudes 

When I was a helper I rode with a few old techs that took it as their life mission to teach me all about every possible nasty thing they could pump into my mind. I started in the trade at 17, home-schooled, wide eyed and as sheltered a Christian kid as you can get (almost). These guys started in using words and pushing mental images I didn’t even understand at first.

Once I got into my own van I was glad to have a break from it… until I started getting trainees. I had three guys that rode with me that I remember in particular who ONLY wanted to talk about what they did, saw or thought about last night. One of them used to be a “tech” (used loosely) in Miami and if I took him at his word he slept with 120% of the of the occupants of South Florida. Needless to say, the fantasy game is strong with most of these guys and I didn’t take a word they said seriously.

Does it shock you that none of them worked out as techs?

The Phone Lookers 

I’m thankful that I started in the trade during a time of radio dispatch before cell phones were popular and even before Nextel chatter became a thing (remember Nextel). Back then our favorite entertainment was listening to little dispatch dramas and techs helping one-another with diagnosis.

Nowadays many helpers / trainees / apprentices and techs alike turn to their phones for entertainment between calls. If you have had a young person working with you who was on there phone all the time how did that work out for them?

The Random Guesser 

I once rode with a guy who would guess what the next problem would be before we got there.

“This one is gonna be a coil leak” he would state confidently 

This was before detailed, web based job histories were a thing so it was really just a total guess based on the type of equipment common in a particular community.

He actually wasn’t a bad tech and this was just his way of entertaining himself, but his method of pre-diagnostic guessing was all based on the dreaded “I’ve seen that before” rather than a solid diagnostic approach based on observation and measurement.

The common thread? All of these techs were busy engaging (or disengaging) their minds in lot of things that weren’t making them better at their jobs.

The Diagnosis Game 

There were a few techs that really taught me and this teaching often happened on the drives between calls and it came in four flavors

  1. Discussing what and why we did what we did at the last call
  2. Explaining technical concepts and practices I was struggling with
  3. Talking through strange diagnostic issues they had experienced in the past
  4. The Diagnosis game

Different people do the diagnosis game differently and probably also call it different things (some of you may not be comfortable with “games” at work) but it has some common elements and is designed to challenge the helper to think and imagine their way through a diagnostic scenario.

Here is how I do it –

Me: Ok, I’ve got one 

Trainee: You’ve got one what? 

Me: I’ve got a diagnosis for you 

Trainee: OK, what is it? 

Me: I’m a service call so you can ask me questions as the customers or choose to check various things and ask me the findings until you make a diagnosis

Trainee: OK so what’s the suction pressure 

Me: Is that how you start a service call? Come to screeching halt in front of the home, hop out and check suction pressure? 

Trainee: No…

Me: Ok, so what do you do first?

Trainee: Check the thermostat I guess

Me: So you come to a screeching halt, jump out, slam open the customers door and start checking their thermostat?

Trainee: (rolling eyes) No… I guess I talk to the customer 

And I just keep going and going and going like this, picking on every detail of the call and diagnosis process they use, detail by detail until they gather enough information to make a diagnosis.

Along the way they will inevitably say something like –

Trainee: Is it a bad capacitor?

Me: Can you ask an air conditioner questions? 

Trainee: No 

Me: I only answer yes or no questions about observable facts, provide you tool readings or answer questions as the homeowner 

Trainee: OK, does the contactor have power? 

Me: What does that mean?

Trainee: Is there power going into the contactor? 

Me: What is power? 

Trainee: Is there VOLTAGE at the CONTACTOR! 

Me: Where at the contactor? 

Trainee: The HIGH VOLTAGE! 

Me: Measured with what? 

Trainee: MY METER! 

Me: What setting on your meter? 

Trainee: VOLTAGE! 

Me: OK, Where are the leads placed

Trainee: Across the bottom of the contactor I guess? 

Me: Don’t guess, what is the bottom side called

Some of you are reading this and getting annoyed thinking I’m a pedantic nerd who just like to antagonize helpers (which is somewhat true I will admit). Some guys hate this at first, but they usually come to enjoy it EVENTUALLY and it teaches imagination, reasoning and precise language.

Along the way you can throw in little scenarios where they die or get injured because they forget to double check their meter to a known power supply or fail to wear PPE etc…

Yes, it’s a little dramatic but the human brain is hardwired for story and competition and the diagnosis game used both of these human traits to help teach HVAC/R. It is better than classroom training because they get to apply and test what they are learning as they are thinking about it, it works best if they actually think you are wrong on something and have to come up with proofs or experiments to try and prove you wrong.

So I posted on social media a few weeks ago about how I don’t like it when trainees sleep in the vans and I got pretty well roasted for being a judgmental sleep hater and after all “what do I expect trainees to do while riding along?”

I expect nothing

One of my political heroes (who will remain unnamed) was once asked how he kept his sanity working in DC with so much corruption and lunacy, he responded

It’s Simple, I’ve just learned to have low expectations  

While I fully expect trainees to fall asleep, look at their phones, guess at diagnosis, fail to read manuals and share inflated escapade stories my STANDARD is that they will actually engage their brains and learn about HVAC/R (and hopefully some life lessons) when they work with me. This is a process and the diagnosis game is one of my favorite tools to get them there.

I firmly believe that anyone who really wants to learn this trade can become usefully proficient much faster than most think possible if they just spend their work day engaged rather than relying on osmosis to fill their brains with experience.

Many of us learned this business because we really had no choice but to make it work and necessity forced us to turn on our minds and make it happen. Some of the people who train with you may not have those pressures and may not have influences in their lives that require then to be on the ball.

You don’t need to be a jerk to hold new people to a high standard, I would suggest step one is to have low expectations and step two is start requiring more of their attention during drives investing in them and bringing them up to your standard.

And trainees… Don’t sleep in the van or stare mindlessly at your phone. Trust me.

— Bryan

A good leak detector is a big investment and one of the more important tools a tech has on the truck. I’ve had the same leak detector for years and I’ve replaced everything on it from sensors to pumps to the probe.. and no, the one shown above isn’t mine.

One thing that I have learned is that with leak detectors care, maintenance and testing is a huge part of finding leaks the first time and will also save you a lot of money. This little tutorial covers the Bacharach H10 series but many of the tips apply to most detectors.

Keep it Clean and Dry

Leak detectors don’t like moisture and dirt. Make sure to keep the rubber tip and filter on the end to help prevent creating a seal that pulls in moisture and keep the detector off the floor and out of the dirt. If you ever DO get your detector wet, shut it off quickly, pull out the batteries (if it has them) and put them in a degassing chamber and pull a vacuum on it. This will dehydrate the detector and can often save it.

Store it in a Safe Place

Leak detectors have sensitive pumps and sensors in them that can be damaged if they are handled roughly. Also, keep from kinking the hoses or probes as this can cause leaks in the tube that will impact your reading as well as restrict flow to the sensor.

Confirm Flow

The H10 series of leak detectors has a red ball flow indicator in the probe. The first thing I do when I start the detector and allow it to warm up is to check the flow through the probe by pointing it down and seeing is the red ball floats.

Check your Sensor

Make sure your sensor is properly connected and on the H10 you can physically feel the heat from the sensor guard door when the unit is running.

Adjust the Sensor

On the H10 you can use the adjustment on the bottom to increase the current through the sensor as it ages to maintain performance. Make sure to adjust it back to the starting point when you install a new sensor to extend the life of the sensor.

Use a Reference Leak

I see many techs attempt to use a bit of refrigerant out of a tank to test their leak detector. With most detectors having a published leak detection accuracy of 0.10 oz per/yr this is a really rough way to test a detector. The best way is to use a tiny calibrated leak or a leak reference bottle like the one shown above to ensure that your detector is going to find small leaks as well as large ones.

If you treat your detector well and confirm the operation of it every time you use it, you should get great results and a long life.

— Bryan


These are two separate emails that I sent to our customers and staff in preparation for what could be a very hot Memorial day weekend (2019). I’m sharing it here so that you can use parts of it in your business as you see fit. I hate seeing techs get beat up on hot holiday weekends so hopefully this helps ease the pain if even just a little. Stay safe out there!

We Have a HEAT WAVE COMING in a Few Days!

I’m not sure if you’ve taken a look at the weather forecast for Memorial Day weekend but it is looking like it’s going to be BLAZING!

There are a few things to consider that could pose an issue for some of you that you should be aware of

  • If it hits the forecast temperatures it could be the hottest days we’ve seen in over a year. Really hot days can reveal issues with air conditioning equipment that don’t usually show up
  • These FIRST hot days of the year are coming on a holiday weekend. A/C companies will have limited staff working and supply houses will be closed.
  • In Central Florida A/C systems are generally designed to maintain 75° inside on a 93° – 95° day. When the temperatures get up to near 100° you may not be able to keep your home below 80° inside. If there is ANYTHING wrong with the A/C this can be even worse.

Take Action This Week Before The Heat Hits

You are getting this email because at one point in time you’ve done business with Kalos. Rest assured this email isn’t about marketing, if you have another company you work with now then the same applies with them. In the A/C business we are used to dealing with a hot “first day of Summer” as well as a hot holiday weekend but NOT both at the same time. Please read below and consider taking these actions on Monday 5/20 before the heat hits.
  • If you have ANY concern that your A/C may not be working the way it is supposed to then get a service call to check it out early in the week so it can be addressed (or given a clean bill of health) before everyone is swamped. We charge ***Redacted*** for a diagnostic service call which is cheap insurance and you can either call or text us at ***Redacted*** (Or use whomever you prefer). It is too late to schedule a tuneup / cleaning / maintenance for next week unless it is already on schedule but you can still get a full checkup which we call a diagnostic service. 
  • If you are sure your A/C is working OK make sure your air filters are all fresh and clean and as the days start to warm up make sure doors stay closed and blinds, curtains are closed.
  • If the weekend comes and your thermostat starts to rise and the the A/C runs all the time, try to stay calm. Don’t call an A/C contractor UNLESS the thermostat rises above 80°. I know it can be frustrating but this is how systems are designed in Florida because we cannot oversize them due to humidity.
  • If you think your A/C is on it’s last leg and needs replaced we can get that setup for a free consultation and estimate during the week next week. Keep in mind the installation schedule will fill up REALLY quick for the week after Memorial day.
There are a few other practical things you can do to keep your home cooler that don’t involve the air conditioner at all.
  1. Replace Halogen and Incandescent light bulbs with LED, they produce less heat. Led recessed can trims can also reduce attic air leakage into the home.
  2. Don’t cook on the stove or oven during really hot days, Hot days = PIZZA!
  3. Run fans when you are in the room, don’t run them when you aren’t. Leaving fans running in rooms you aren’t using actually INCREASES the temperature of those rooms. Fans cool you via convection and evaporation they don’t decrease the air temperature.
  4. Get insulation added to your attic. If you call an insulator early this week they may be able to get it done before the weekend hits. That’s a win -win because it helps with your power bill and comfort on hot days.
This next piece of advice is worth the price of the email so pay close attention. If you get into the heat of the weekend and your thermostat starts to rise there are two secret HVAC technician life hacks you can use to make things a little better for a short period of time.
  1. FIRST, go outside and place your hand over the outdoor fan. If you can hear it running and the air blowing out the top feels hotter then the outdoor air then the compressor is running. If not then shut the system off and you will need to schedule a service call.
  2. Look all around at the pipes going into the unit. If you see any ice, go inside and turn the unit to OFF and the fan to ON at the thermostat. Leave it this way for 8 hrs or so to defrost the unit. If you call out a tech and they show up to a frozen unit it will result in delays and/or extra charges. Keep in mind that when the unit defrosts the part inside (the furnace or fan coil) may leak some water so be prepared with towels around the inside part of the air conditioner. If there was no ice then go to step 3 
  3. If the unit is blowing out warm air outside and there is no ice you can see anywhere and your filter is new and clean you can use a lawn sprinkler to mist water onto the side of the outdoor part of the air conditioner. Make sure it is low pressure and only do it for a maximum of 6 hrs a day and only for a few days a year during the hottest parts of the day. This helps to improve the capacity of the air conditioner and takes some of the load off of the compressor. DO NOT DO THIS LONG TERM, CHLORINE AND MINERALS IN THE WATER CAN AND WILL DAMAGE YOUR AIR CONDITIONER. 

Finally, If you do need a service call you can call or text us at ***Redacted*** but PLEASE be patient. We are doing everything we can to get ahead of the weather but the technicians who will be working during Memorial day weekend are going to be under a lot of pressure. Some of them are Veterans who have served our country and all of them care deeply about doing a good job for our customers.

Sometimes your best option may be to get a hotel for a night or two if your A/C goes down during a time like this while waiting to have it repaired. You may also consider getting a portable A/C from a big box hardware store to keep the master bedroom cool.

As a customer of Kalos you are a huge priority to us but caring for our team members and their families are still priority #1. For us this means shutting down the schedule for the day at midnight so our techs can get a few hours of sleep before they start the next day.

Rest assured that if you need us we will do everything we can do to help while maintaining the health and sanity of our staff.

Thanks for being a Kalos Customer, I really appreciate you.

— Bryan Orr


Hello Everyone,

I may be overreacting but as they say “Fate favors the prepared”… Don’t they say that? I’m sure somebody does.

The current forecast shows high temperatures of 98° on Memorial Day Weekend. This is not ONLY high temperatures on a weekend when supply houses won’t be open on Monday (although we can always make them open if need be) but it will be the hottest day of the year and MAYBE the hottest day in several years.

This means a few things,
Monday 5/27 will be a full staff work day for service employees just don’t forget to honor those who gave the last full measure of devotion to our Nation as we serve our customers.
All managers will need to be ready to assist on 5/25 & 5/26 (Including Myself)
Anyone who is willing to help out on the evening of 5/24 – 5/26 will be most appreciated from installers to refrigeration techs to CSRs to parts quoting. Anyone who can grab a service call or a phone call will be appreciated.
Have your trucks stocked and ready to rock. If a real emergency occurs and we need a part from a supply house, especially for Warranty or contract customers then almost all suppliers have emergency lines and we should use them, if we are miserable then they can be as well.

Keep a cooler or case of water on your truck, grab it from the shop or use your card to get it if need be. STAY HYDRATED.

If it is as hot as forecast we may need to prioritize calls. The first thing is that from Saturday 5/25 – 5/27 we will be charging a ***Redacted*** diagnosis fee for non-contract / non-warranty residential customers for the holiday weekend. If the customer asks why just say it is the holiday charge.

We will prioritize customers in this way for service

*** Customer Name(s) Redacted *****
Commercial Refrigeration Warranty Work & Callbacks
Residential Warranty & Callback Customers
Residential Contract Customers
Regular COD customers of all types
Ductless Lanai / Florida Room Units (Schedule for the week)
When we schedule over the weekend we need to use VERY wide windows for any COD customers we put on schedule. Do not schedule any calls for ductless systems on the holiday weekend, these are not emergency calls and should only be scheduled during regular hours on weekdays. If these customers get cranky keep in mind that we NEVER promise 24hr or weekend service to residential customers unless they have a specific contact to that effect.


Whenever we have days where the outdoor temperatures get above 93° you will have some customers that call in because their A/C is not keeping up or because it “runs all the time”

In Florida we have ACCA (Air Conditioning Contractors of America) guidelines for design and 93° – 95° are used as the design outdoor temps. This means that on a 98° day many systems may not maintain 75° and may go up as high as 80°. When a customer calls in and says the temperature is going up in the house we can ask what the thermostat says the indoor temperature is. If it is 80° or lower at 2PM – 9PM of a 98° Summer day then there is likely nothing wrong with the system so long as it is running. For the skeptical client you may send them this link **redacted**

If as a technician you go to a call on a callback or warranty job for not keeping up or running all the time you need to do the following steps

Perform all of your normal visual inspections and measurements ( Filter, coils, thermostat calibration, subcool, superheat, delta T, Amps, Voltage) if all this check out then
Check static pressure and visually inspect ducts and attic insulation – if all this checks out then
Do a full MeasureQuick PDF report and send it to ***Redacted*** so we can be aware and upload to the file…. What? You say you DON’T KNOW HOW TO DO THAT? well… you have a full week to figure that out.
If the customer is COD then we do the basic tests and OFFER the Attic inspection for ***Redacted*** to check ducts and insulation on a basic small house or ***Redacted*** if it will take over 30 mins.

When we find a house where the A/C is working properly (based on all these tests, not “BEER CAN COLD” or suction pressure) then we do NOT tell them their A/C may be undersized… The resolution is almost ALWAYS in decreasing heat load on the space not increasing system size. This includes items like –

– Sealing Gaps to the attic
– Replacing incandescent light trips with sealed LED
– Upgrading Attic Insulation
– Closing Blinds and Drapes
– Keeping doors closed
– Upgrading Ducts

If a system is LEGITIMATELY undersized it’s generally better to carve out a room and add ductless rather than trying to up the tonnage of the old A/C and upgrading ducts + trying to make it fit in the same space.

MeasureQuick system reports will be your best friend in helping you PROVE that the A/C is working properly in cases where the customer is stuck on the idea that there is a problem and it only takes about 10 mins to do completely.

The goal is all pitch in to get our customers taken care of without kicking a bunch of callbacks or cranky customers down the road into the next week. Weeks like this can either be a profitable kickoff to the Summer or a miserable mess depending on how we approach it.

My Cell is ***Redacted*** if you need me. I will have it on and with me.




I recently received a message asking for a discussion of RH. WB and DB. Time and time again I hear techs say that condensation occurs when “hot meets cold” which may be true in some cases but that is only a shorthand way to describe it and doesn’t really address what is going on when we see condensation and undesirable growth.

RH = Relative Humidity as in the percentage of humidity relative to the amount of moisture can hold at that temperature.

I like to think of it like sugar in a cup of coffee. The hotter the coffee the more sugar the coffee can hold.

When we say the air is “humid” we can mean it contains a lot of absolute moisture in grains or pounds or we can mean it is high “relative” humidity which is the more common meaning. 95 degree air at 50% RH contains far more moisture in lbs per lb of air than 65 degree air does at 50% RH does.

It’s a common misconception that hot air is more humid. While it’s true that hotter air can hold more moisture in the same way that hotter coffee can hold more sugar it does not mean hotter means more humid. In fact, if you heat a mass of air and the amount of moisture doesn’t change the RH will go down as the air gets warmer. This is why the RH coming out of the top of a furnace is lower than the RH going in. No change has occurred in the actual amount of moisture present, the air is just hotter and therefore lower in humidity relative to how much it can hold.

DB = Dry Bulb and is the temperature of air without taking account for evaporation / relative humidity

WB = Wet Bulb and is the temperature of the air with the evaporative effect of a “wet bulb” taken into account. Quite literally wet bulb temperature is the temperature a thermometer bulb will be when covered in a wet fabric and whirled in the air or placed in an air stream.

If the RH is below 100% the WB will always be lower that the DB. The differential between the DB and WB illustrates the RH. The higher the differential the lower the RH. The lower the differential the higher the RH. When DB and WB read the same then the RH is 100% and the air is “saturated” and no more evaporation can occur.

When air hits 100% RH the dry bulb and wet-bulb temperatures are the same and this point is known as “dewpoint”

— Bryan

A friend of mine was telling me that a utility had the idea that they could reduce energy consumption by turning HVAC equipment on and off rapidly during times of high load. In their minds wouldn’t it be better to spread out the off time rather than keeping the system off for longer periods and allowing the space to become uncomfortable?

The answer is a HARD NO on that one!

Short cycling is a condition where equipment goes on and off more than is optimal, each time it goes on and off is called a cycle and we (almost) always to keep run times long and cycles to a minimum. Sometimes short cycling occurs due to a system fault and sometimes it occurs due to a mismatch between system capacity and load (cooling or heating too quickly).

Short cycling is a problem for many reasons including poor temperature control, inadequate dehumidification, rapid component failure and the list goes on and on. RAPID short cycling can quickly cause contact and relay failure due to arcing and can be very damaging to motors.

Let’s look at some common conditions that cause short cycling –

Safeties, Limits and Pressure Switches 

Anytime there is an issue with the equipment that causes high temperatures or and high/low system pressures there are often controls that shut the system off before a catastrophic failure occurs. Some common examples would be –

  • Furnace limit switches
  • Compressor and other motor overloads
  • Refrigerant High, Low and Loss of Charge pressure switches

When one of these safety controls turns the system off there will often be a time delay that prevents the equipment from coming right back on. In most of these switches there will be a gap between the make and break (on and off) points in the switch which will naturally help to prevent rapid short cycling.

Loss of Power

When power is rapidly cycled (turned on and off) the components may go off then back on quickly if there is no time delay. Here in Florida this happens often during thunderstorms but it can also be caused by flipping a breaker on and off rapidly or bumping a condensate switch. These sorts of rapid short cycling events are hard on motors and controls and can even cause scroll compressors to run backwards (on rare occasion).

Oversizing / Low Load 

The way we control temperature with most appliances is by running them until they hit setpoint and then shutting them off. This can result in short run times when the load is low or when the equipment is oversized. The best designs result in the equipment running non-stop when during peak load, this isn’t intuitive for most customers and they will often complain that the system “never shuts off”, you can reassure them that so long as they are staying comfortable, never shutting off is a good thing for system longevity and power consumption.

Controls Design & Setup

The controls play a big part in run time depending on how they are setup. It is almost never as simple and turning on and off at a set temperature because that would almost certainly result in short cycling unless the system has variable capacity or the capacity is perfectly matched to the load. In most real world conditions the controls will need to manage a deadband or gap between on and off to balance comfort and short cycling.

Controls do this by maintaining and on off dead-band and maintaining a maximum CPH (cycles per hour) like the Honeywell thermostat shown above. This means that a thermostat with a 3 degree dead-band with a cooling CPH set to 3 and a set-point of 75 degrees would come on at 76 and shut off at 74 while turning on and off a maximum of 3 times per hour.

So these are some of the factors that impact short cycling but what are some of the issues associated with short cycling? here is an incomplete list –

  • Electrical System Strain / low voltage to the rest of the structure during motor / compressor start up
  • Dimming lights
  • Contactor / Relay contact wear
  • Premature HSI (Hot Surface Ignitor) Failure
  • Compressor oil loss and lubrication issues
  • Poor dehumidification (It takes a while for the coil to cool down and dehumidify)
  • Poor efficiency and system performance (It takes time for the system to get up to steady state performance)
  • Poor Cooling / Heating (When you short cycle you may heat and cool the air rapidly but may still have “stuff” in the home and structure that are hotter or cooler resulting it radiant discomfort)
  • Poor ventilation control

I’m sure you can think of many more.

The goal is to run long and steady cycles without any cutting in and out safeties and a good match of system capacity with the load. This helps us provide comfort, efficiency and  system longevity.

What are some short cycling issues you have seen?

— Bryan


Every piece of air conditioning equipment is capable of moving a certain amount of heat BTUs (British Thermal Units) at set conditions. In most cases during the cooling mode, a portion of those BTUs will go toward changing the temperature of the air and a part will go towards changing vapor water in the air into water that collects on the evaporator and then drains out.

The BTUs that go towards changing the TEMPERATURE of the air are called SENSIBLE and the ones that go toward removing water from the air are called LATENT. The percentage of the capacity that goes toward sensible cooling at a given set of conditions for a given piece of equipment or space is called SENSIBLE HEAT RATIO (SHR). So a system that has an SHR 0f 0.70 and 30,000 Total BTUs of capacity at a set of conditions would produce 21,000 BTUs of sensible cooling and 9,000 BTUs of latent removal because 30,000 x 0.7 = 21,000 and the rest 30,000 x 0.3 = 9,000.

Higher SHR (closer to 1.0) = More change in temperature and less humidity removed

Lower SHR = less change in temperature and more humidity removed

In the HVAC industry, there is a set of standard conditions used to compare one piece of equipment to another. When a system has an SHR rating listed it would often be at AHRI conditions unless the specs state otherwise.

When doing a load calculation a good designer will calculate and consider the internal and external latent and sensible loads and match up with equipment accordingly based not only on one set of design conditions but on the range of seasonal and occupant conditions that the structure is likely to experience based on the use, design and climate. By following ACCA (Manual J & S) and ASHRAE (62.2 & 62.1 for example) standards a designer will have guidelines to follow and this includes matching the space SHR to a piece of equipment that will make a good match at similar conditions. It does often need some digging into manufactures specs to interpret this data for the equipment.

In the example above from a Lennox unit, you can see that the SHR is listed and highly variable based on outdoor temperature, air flow setting as well as indoor wet bulb and dry bulb temperatures. In this example, you would need to multiply the total capacity x SHR to calculate the actual sensible and latent capacity.

This example from Carrier has no SHR listed, instead, it lists the specific sensible and total capacities. You can easily calculate the SHR by dividing the sensible capacity by the total capacity and the latent is simply the sensible subtracted from the total.

The cool thing is that this understanding can help both designers and commissioning technicians to match equipment properly and even make further adjustments using airflow to get a near perfect match which leads to lower power consumption, less short cycling and better humidity control.

— Bryan


The most common method to defrost appropriately in refrigeration involves both time for initiation and a combination of time and temperature for defrost termination (ending defrost).

But why can’t we just use temperature or time alone? (you may wonder).

Imagine a common freezer with a designed box temperature of -10°F and a coil temperature of -20°F. Periodically the evaporator coil will need to defrost and the amount depends on how much moisture is brought into the box from opening doors and new product being added.

How could we possibly tell when the coil needs to defrost by temperature alone? The coil is already 52°F BELOW the freezing temperature at design conditions. Whether the coil has a lot of ice on it or very little it will still be cold enough for ice to form so using the temperature of the coil alone is a poor indicator of when a defrost is needed (initiation of defrost).

So what if we used time alone? It is common to setup freezers for 2 (dry) to 6 (Humid) defrosts per 24hr period depending on the climate and how they are being used. You would then setup a length of time for the defrost as a best guess with too long wasting energy and warming the product or too short resulting in incomplete defrost and gradually freezing the coil.

With this time only strategy you are left guessing and in order to prevent progressive freeze ups you will always need to defrost a little too long.

So instead we use a combination of time to set the number of defrost occurrences per 24hr period. We use time to make a solid at how long it will take to reliably defrost the evaporator coil and then we use temperature to terminate (stop) the defrost once the coil warms up enough that we are sure it is no longer ice bound.

This combination of time and temperature for defrost termination also gives us a bit of a backup plan. If the temperature sensor or thermostat isn’t working correctly it will still go back to refrigerating once the time is complete. If the time is set way too long for defrost the temperature termination will stop the defrost and send it into refrigeration mode before the product gets too warm.

This is why it is common to initiate defrost using time and terminate defrost using temperature and time.

You can think of it like a irrigation timer that uses a time schedule to water the lawn but it can ALSO use a rain sensor to prevent it from watering when it just rained.

This same strategy of time and temperature is also used in many comfort heat pumps to defrost the outdoor coil in heat mode.

— Bryan

In Residential and light commercial HVAC we work primarily with PSC (Permanent split capacitor) motors. However, there are some other types that are good to be aware of.

PSC (Permanent Split Capacitor)

A common medium torque single phase motor with a run capacitor always in the circuit. This type makes up the majority of HVAC motors (condenser fans motors, blower motors compressors)

CSCR – (Capacitor Start, Capacitor Run)

A higher starting torque motor that uses a run capacitor as well as a start capacitor. The start capacitor is removed from the start circuit shortly after starting using a potential, current or centrifugal relay.

CSIR – (Capacitor Start, Induction Run)

These motors are fairly rare and utilize a start capacitor and no run capacitor.

Three Phase

Three phase motors require three phase power and do not require capacitors.

Shaded Pole

Shaded pole motors are very small, low torque motors. They can only run in one direction and they do not utilize capacitors.

D.C. (Direct Current) 

D.C. Motors work on Direct Current and (generally) utilize brushes to transfer an electrical charge to the armature (rotor) of the motor.

ECM (Electronically Commutated Motor)

This type of motor is a high-efficiency  DC (or three phase depending on how you look at it) motor that uses no brushes, a permanent magnet rotor and utilizes electronically switched DC power to turn the motor at various speeds.


— Bryan

I am consistently surprised by how much false information still circulates out in the field and one of the ones I hear often is the idea that you cannot or should not “top-off” or recharge R410a systems on top of an existing charge of R410a when the system is low.

So to be clear before we move on, it is 100% OK to add to an R410a charge without fear of any significant fractionation. If you doubt me, you can read THIS from Dupont/Chemours.

R410a is a near-azeotropic blend of 50% R32 and 50% R125. This means that while it has a tiny amount of temperature glide you can still work with it like a zero glide (azeotropic) refrigerant for all practical purposes.

The fear that some have is that if the refrigerant leaks out in vapor phase, one refrigerant will leak at a higher rate than another which could change the blend as it leaks.

While this can (and does) occur with high glide refrigerants, it has been proven that this is most likely to occur in very slow leaks during long periods of storage when the refrigerant is not moving. An example would be a high glide blend in a tank with a slow leak at the valve on top. This is the worst case scenario and an example of where fractionation can be a real issue.

In a running system or a system that runs most of the time, it is unlikely that fractionation would pose an issue because the movement of the refrigerant in the circuit mixes the refrigerant and prevents one part from leaking significantly faster than another. This study by Purdue covers this as it relates to flammability risks.

The practice of charging blends in liquid phase still makes good sense because fractionation, to the extent it occurs is still most likely to pose an issue in a static vessel like a tank and charging in the liquid state is just cheap insurance against fractionation.

But once again… It does no harm to top off an R410a system with R410a. This is NOT to say I’m advocating recharging systems without finding and repairing leaks where possible, just that fractionation isn’t a reason not to do so.

— Bryan

A while back I had a tech who was having some trouble finding a 35 PSI(2.41 bar) make on fall pressure switch. In the catalog, one adjustable switch said (SPDT) but he didn’t quite understand what that meant. In that case, it means single pole, double throw, and the “double throw” part means that the switch has terminals in both the close on rise and close on fall directions. Another common example of this sort of switch is a “3-way” light switch.switches

A single pole, single throw (SPST) switch is like a typical light switch. It only has one path (pole) and it is only closed or open.

A double pole singe throw (DPST) switch that is quite common is a 2-pole contactor. It has two switches but they only open and close in one direction.

A common double pole, double throw (DPDT) switch in HVACR is the 90-340 relay (and many other relays), where it has two circuits and they alternate between closed and open terminals.

— Bryan




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