Month: May 2018

This article is written by my good buddy Bill Frisbie. Service manager and crack technician at AirFx, a Trane dealer in lovely Inverness Florida. Thanks Bill!


One of the most intimidating things in the field is to walk up to a piece of equipment that you have either never worked on, or you just don’t understand. One of the most misdiagnosed systems is the Trane Hyperion air handler, more especially the Tam7, or Aam7 (American Standard). The most common issue they’ve had is the sensors that connect to the EVC board, and one attaches to the suction line, much like a sensing bulb, and the other is after the EEV and entering the coil. The black lead goes to the gas sensor (suction) and the orange goes to the ET sensor (coil entering.)

In order for the system to function correctly, these sensors must be able to accurately read those temperatures, and there is a chart that helps us check those values on site.

Another common fault has to do with the way the float safety is tied into the system.  When the float trips (opens), the loss of voltage should occur between the thermostat and Y1 before entering the board. If you break the circuit between the board and the condenser, the condenser will not run, however, the EVC does not know the outside is not running. The EVC continues to monitor evaporator temperatures, it thinks that the superheat is incorrect, and can cause a fault. To fix this, simply confirm the wiring is correct, and of course make sure the drain is clear.

The system also has test pins located at the bottom front of the EVC board, that you can test open and closed, to make sure the stepper motor is working. Although they can be bad or plugged, it’s been very rare in my personal experience, to have a bad EEV valve body. Our company installs 10-12 systems per week on average, and I’ve replaced 2 in 7 years.

As far as the actual EVC board, I may personally have 5 changed in 7 years. There is also a chart to check the stepper motor, and can tell you if it’s bad, but that’s also pretty rare.

A more common issue would be the wire harness that connects the board to the coil. I’ve had several where the harness has a wire that does not make contact through the plug, or an installer has drilled in a bad area to attach something to the cabinet, and damaged the wire buried between the inner and outer panel. One fairly common issue is also having the dc voltage control fail. Its located left of the door switches and has 240 v entering, and 13.8 VDC leaving to the AFC board. Every failure though is because a bug has gone between the plate and board, and caused a short.

 

I’ve come up with a simple image that our technicians have as a resource on site, so they can confirm the boards have communication and control voltage where it needs to be.

Included is a PDF of the Tam7 service facts sheet that can help as a guide to help with troubleshooting in the field. Once you get the hang of it, its really a solid piece of equipment, and fairly easy to repair.

— Bill

 

I bought a crappy old house that was built in the 1920’s a few years into marriage and there were so many things wrong with it. Water intrusion, leaking pipes, roots in the sewer line… on and on… but it was ours and we loved it.

One issue was the water heater was tiny and it was in the attic with no room to make it larger. I couldn’t even make it through a shower without running out of hot water. So what did I do? I jacked up the thermostat!

My wife washed dishes the next day and was not amused at the blazing hot water that came gushing over her hands. I’m glad I listened to her and set it back down, because not only was it safety hazard it was also a waste of energy.

So much of what we do is about controlling the temperature of air, fluids and objects as well as the rate of transfer of heat from one to the other. We can impact this rate of transfer by changing the distance between the objects, changing their temperature differential or changing the resistance to energy flow or R-value.

In the case of the water heater, increasing the temperature of the water in the tank and in the pipes increases the rate of energy loss through the tank and pipe walls as well as being a safety hazard. This is why the Department of Energy suggests setting your water heater thermostat to 120ºF which is 20º lower than many manufacturers even set it.

In addition to changing temperature differential, we can insulate to reduce energy transfer. We insulate things for three primary reasons

  1. To reduce the rate of heat (thermal) transfer from hot to cold for efficiency or comfort
  2. To keep the temperature of a surface above dew point to prevent condensation and water damage
  3. To protect safety from scalding or frostbite

The IMC (International Mechanical Code) 2015 edition 604.2 surface temperature states that ducts that contain air of over 120º must have enough insulation so that the external surface doesn’t exceed 120º. This serves as a high limit for duct temperatures for safety reasons, but it also has practical energy application as while.

While locally adopted mechanical and energy conservation codes will generally require certain insulation R-value for ducts you can use this 120º surface temperature as a litmus test. On the other end of the spectrum, a duct surface temperature should never be allowed to fall below the dew point temperature of the air surrounding it. This can be quite tricky in humid climates where ducts are installed in unconditioned spaces but should be considered nevertheless.

So be safe, efficient and stay dry by keeping your ducts and water properly insulated.

— Bryan

First off we need to clarify that very few unitary manufacturers use flares anymore. You will most often find flares on ductless and VRF / VRV systems and in refrigeration. A flare uses a flared female cone formed into tubing (usually copper) that is pressed onto a male cone (usually brass) by a threaded flare nut. A flare shouldn’t be confused with a chatleff fitting that uses a threaded nut and seals with teflon or nylon seal.

This is not a full lesson on how to make a flare, this will give you some best practices to make a flare that doesn’t leak.

  • Use proper depth, the old school method is to bring the copper up a dimes width above the block but modern flaring blocks usually have built in gauges that work well.
  • Don’t trust factory flares. In many cases factory line-set flares are made poorly, often it’s better to just cut them off and start over
  • Ream the copper before flaring to remove the burr but don’t OVEREAM and thin out the copper edge.
  • Use a good, modern flaring tool designed for refrigeration. This is a great one
  • When making the flare use a bit of refrigerant oil, or even a better a bit of Nylog. You only need a drop or two, one drop on the flare while making it to prevent binding and create a smoother flare surface with a bit on the back of the flare as well to allow the nut to slide easily. I also like one small drop on the threads and spread to the mating surfaces. Some manufacturers disagree with this due to the effect it has on torque specs so always follow their recommendations when in doubt. In my experience a bit of assembly lubricant really helps.
  • Use a flare wrench instead of an adjustable wrench and tighten with a torque wrench.  I understand that very few techs do this… but it is a great practice if you want to get it right the first time with no leaks and no damage. This can be done easily be done with a set of SAE crowsfoot flare nut wrenches and a 3/8″ torque wrench. As always use manufacturers torque specs if available. If not you may use the chart below. Make sure to keep the crowsfoot at 90 degrees to the wrench (perpendicular) and place your hand on the end grip of the wrench. If you have lubricant on the threads stay on the low side of the torque rating.

Some things NOT to do that I’ve seen –

  • Don’t use leak lock or teflon tape on flares
  • Don’t Over Tighten flares to try and get them to stop leaking. If they are properly torqued and still leak they are made wrong
  • Don’t use too much oil or nylog, a drop or two will do
  • Don’t try and jam a teflon seal from a chatleff on a flare

Using these practices we have VERY FEW leaks on flare fittings.

Some other things to note –

There is a company called Spin that uses a flaring tool that goes on a drill. Their tool actually heats and anneals the copper. They claim they don’t need to get the flare to 45 degrees because the annealing makes the copper soft enough that the nut itself with finish the flare. We have used it a few times with good results.

There are now companies that make nylon / teflon (I’m actually not sure what they are made of) gasket inserts that go into a flare. Some techs swear by them, I really don’t see the necessity but I don’t have any experience with them.

Finally, make sure when your system has flares to pressure test to the rated test pressure and bubble test the joints. Then perform a vacuum to below 500 microns and decay test. This will help ensure that you got it right. If it leaks, cut it off and remake it.

  • Use a good tool
  • Get depth correct
  • Ream properly
  • Use a good assembly lubricant
  • Torque properly
  • Pressure test to 300+ PSIG (in most cases) and bubble test carefully

— Bryan

Tunnel Vision and How To Avoid It

How many times has this happened to you: You’re on your way to that final service call. While you’re listening to the customer explain their complaints over the phone, there’s this precise moment where you’ve thought: “I know what it is already. This will be a quick one.”

Sometimes intuition proves to be a useful tool for an efficient service technician, but that same intuition can bite back fiercely if it leads to ignoring the whole picture.

Let’s take a simple example. The customer reports that their unit isn’t cooling very well and it seems like it’s running longer than normal. The immediate thought may be that the refrigerant charge is low. Reading the pressures on site, it’s discovered that the unit has lost most of its charge. While it can be tempting to restore the refrigerant charge, find the leak, and write up the repair to keep moving, it’s vital to evaluate the rest of the system before proceeding.

Failing this can lead to upset customers who, after paying for the initial service, can face the prospect of additional repairs. Here are a few simple steps to avoid this pitfall:

  1. Listen closely to the primary complaint and address this problem first.

  2. Take care to note any contributing factors to the primary complaint. Ask yourself questions like: “What caused this problem in the first place? Could this happen again if these conditions persist?”

  3. Watch out for any other potential failure points unrelated to the primary complaint.

  4. Document all findings in detail and take the time to explain why each concern is valuable to your customer.

Taking these few extra minutes on the initial visit can save you and your customer precious time and frustration. Resisting the temptation to only solve the first problem will often lead to a more fruitful service call. Nothing beats the peace of mind that comes with a thorough diagnosis.

– Zach S.

Let’s first state the obvious. Most techs are intimidated by Psychrometric charts and Mollier diagrams, we JUST ARE. While there are some pretty complicated formulas that back up these diagrams, using them isn’t a big of a deal once you understand the different elements and then focus on one at a time.

BUT WHY DO YOU CARE?

Dew point is one example of a very useful measurement to understand, design for and test for in an HVAC/R system. Take an evaporator coil, do you know how to calculate the exact temperature at which that evaporator coil will start to condense moisture? can you tell the exact temperature at which a surface inside of a space will start to condensate and possibly grow mold? These are both cases where a basic understanding of a psychrometric diagram can help a technician.

While some of the elements on the chart are represented by curved or slanted lines, dew point temperature and humidity ratio / absolute moisture content are just straight lines horizontally across the chart.

So if we focus on a 65°F(18.33°C) dew point on the right side of the chart you will notice it crosses  over 92 grains (there are 7000 grains of moisture per lb) of moisture line and then goes all the way across until it intersects with the curved 100% humidity line on the left side. This shows us that at a 65°F(18.33°C) dew point the air always contains 92 grains of moisture per lb.. ALWAYS.

This also shows us that when the air is at 100% relative humidity the dew point, wet bulb and dry bulb temperatures are ALL THE SAME.

If we have a dew point of 55°F(12.77°C) the air contains 64 grains of moisture per lb. If the dew point is 30°F(-1.11°C) the air contains 24 grains… you get the point.

So now if you find the dry bulb temperature and the relative humidity you can easily calculate the dew point at which that same air will reach saturation and begin to form condensation.

Let’s say we have 75°F(23.88°C) dry bulb air at 50% relative humidity. We would simply draw a line up from the bottom at 75°F23.88°C) until we hit the curved 50% line. Then go right (or left) until you bump into the the grains of moisture and then the dew point scale. Now you know at what temperature that same air mass will start to condense water.

So we can see that this if this 75°F(23.88°C) dry bulb 50% relative humidity mass of air comes in contact with a surface that is 55.5°F(13.05°C) or less, it will begin to condense water. We also know that this air stream contains 65 grains of moisture per lb of air.

Forgive me for saying so, but I think this is pretty cool.

— Bryan

P.S. – If you want a good quality Psychrometric chart you can use THIS ONE

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