May 2018 - HVAC School

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

Podcast Episodes

Sealing Ducts From the Inside w Sean Harris (Podcast)

May 29, 2018 By HVAC School No Comments

Sean Harris with Positive Energy and Aeroseal Austin sat down with me at the humid climate conference and talked about how to seal ducts from the inside with Aeroseal.

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

Tech Tips

Exposed Duct High Temperature Limit

May 29, 2018 By Bryan Orr No Comments

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

To reduce the rate of heat (thermal) transfer from hot to cold for efficiency or comfort
To keep the temperature of a surface above dew point to prevent condensation and water damage
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

Tech Tips

The Case For Pulling The Blower Housing

May 25, 2018 By Bryan Orr 3 Comments

When I started in the trade in 1999 there were still a lot of oilable blower motors in service. As part of the maintenance, we would remove the housing, oil the motor plus vacuum / wipe it down.

As oilable motors have become extinct I see fewer and fewer techs pulling the blower housing. Here are some reasons you may want to consider doing it more often.

Cleaning the motor itself can help it run cooler and last longer. A hot motor not only is more susceptible to winding breakdown but also to bearing/lubricant failure. Grab a vacuum, soft bristle brush, and a rag and get the dust buildup off the motor. If you have any dust that gets stuck inside, use some low-pressure nitrogen or compressed air to get it clean.
Get in there and look carefully at the wheel. A wheel that is even slightly dirty can have a significant effect on air output. If it’s dirty, recommend cleaning.
Check the blower bearings, it’s easier to do when it’s out
On high-efficiency furnaces pulling the blower is a good way to check the secondary heat exchanger. On 80% furnaces, you can check parts of the primary exchanger and even the evaporator coil with a mirror or inspection scope.
Pulling the blower gives you the ability to wipe down the inside of the furnace or Fan coil.
You can check blower mounting bolts and set screws as well as blower alignment and balance more easily.

Obviously, when and why you pull the housing will vary from contractor to contractor but I advocate it being done more often than it is now.

What say you?

— Bryan

Podcast Episodes

Short #9 – Commercial Maintenance (Podcast)

May 24, 2018 By HVAC School No Comments

5 things residential techs need to consider when tasked with doing a PM on a commercial system.

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

Tech Tips

Making a Flare – Quick Tips

May 23, 2018 By Bryan Orr 3 Comments

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

Podcast Episodes

Air Filters, They are More Complex Than You Knew w/ Lee Andrews (Podcast)

May 22, 2018 By HVAC School No Comments

Lee Andrews with Andrews Filters talks about the complicated and important topic of air filtration and why it matters to you and your customers.

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

Tech Tips

Fan On or Fan Auto

May 21, 2018 By Bryan Orr 4 Comments

Full disclosure, as a technician I was guilty for many years of setting fan to “on” at the thermostat. I never really thought of any of the negative impacts that could happen.
I wanted to circulate the air, and to keep air moving through the high efficiency air filter that most of our houses had. Later I learned that in many scenarios fan “on” is not a good idea.

For this discussion I will be talking about the cooling season in a humid climate. Many adverse impacts may occur in the heating season, depending on the region.

Things to be aware of when running the fan “on”.

Condensate on the coil after a cooling call with the fan running will evaporate back into the living space. Some thermostats combat this by having a fan off period at the end of a cooling call to let the coil drain.

If the ducts are in unconditioned spaces, outside the thermal envelope of the house, the sensible heat will be added back to the space. If the ducts are warmer than the air traveling through them there will be a transfer of heat. If there is any duct leakage latent heat (moisture) will be added as well. Latent heat gains do not only apply to return duct leaks. Supply air leakage can also contribute to this.

It is common that the HVAC system can cause the house to go into a negative pressure. When this happens sensible and latent heat will be added. A common cause of the pressure imbalance is when the duct system is in an attic or crawl space, and the return duct has fewer connections than the supply ducts.

Since the supply has more connections than the return there is more of a potential to leak air. If the supply air leaks into the attic or crawl space this can cause the living space to go into a negative pressure. The leaked air is replaced with either attic, crawl space, or outside air. One CFM(M3/h) in = one CFM (M3/h) out.

Ducts in conditioned spaces with panned returns can add latent and sensible heat as well. This happens when the panned joists and studs are not sealed by the HVAC contractor on all six sides. Joists and studs are part of the building network that when not air sealed during construction, by the builder, they will communicate with air outside the building envelope. With blower door testing, and air changes per hour requirements now code in many jurisdictions houses are being built much tighter. In an older home, with panned returns, expect to be bringing in some outside air.

Even if the ducts are sealed, and 100% in the conditioned space it still costs money to run the fan. Running a PSC motor 24/7 can be costly. (ECM motors on a property sized duct system do have considerably lower operating cost when compared to PSC motors.)

The duct leakages and pressure imbalances mentioned above will also occur during a cooling call. Most of the time these issues can go unnoticed because of the ability of the HVAC system to overcome or mask them.
The goal is to get maximum customer comfort with minimum power usage and maximum system longevity. In many cases the fan being left in the ON position detracts from these goals.

Hopefully this Tech Tip will make you think twice about running the fan “on”. Every situation is different. I encourage you to think outside the box, if you are not already.

— Neil Comparetto

Tech Tips

Connecting Transformers in Parallel

May 20, 2018 By Bryan Orr 1 Comment

I had an old timer tell me that you can never connect two transformers together because they will “fight one another”.

If you are anything like me (and heaven help you if you are), whenever someone says something like that, a cartoon in your head starts playing.

In this case, I imagine two transformers with boxing gloves on duking it out to see which one “wins”.

The truth is you can connect two transformers together so long as you are careful, but you need to know why you’re doing it and then do it properly.

Transformers have a VA (Volt-amps) rating that dictates how many volt-amps (volts x amps, which is watts simplistically but there is a more complicated reason it is called VA in transformers that we won’t get into here) the transformer can handle on the secondary.

Above we show two 75VA transformers with 24V secondary windings.

75VA÷24V=3.125A

So with a 75VA transformer, you can run a maximum of 3.125 Amps, if you needed more power you would need to either go get a larger, more expensive transformer or…. you could connect another identical one in parallel. If you connected two 75VA transformers in parallel you would then have 150VA of secondary capacity which can be necessary in some cases with multistage commercial units or some large accessories.

In this case, parallel simply means connecting the two primary and secondary windings together in the exact same way as we show above… Pretty easy

It is SUPER important to get the polarity exactly the same and use two transformers with identical winding turns in the primary and secondary and identical secondary coil impedance (resistance).

In fact, it is so important that I advise that you only do this if you have two identical model transformers.

To be even safer, connect the primary windings first and check the secondary’s against one another with a voltmeter before actually connecting them to the system. For a typical 24v secondary you can connect the two common wires to ground to act as a stable reference first then check the two R or Hot side leads to one another and then to common. They should read 0v to one another and 24v to common. If you get anything other than 0v from hot to hot then you want to recheck your primary wiring and ensure that they are exactly the same.

— Bryan

Tech Tips

Tunnel Vision and How to Avoid It

May 16, 2018 By Zach Simpson No Comments

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:

Listen closely to the primary complaint and address this problem first.
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?”
Watch out for any other potential failure points unrelated to the primary complaint.
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.