This is a video tech tip from our friend Brad at HVAC in SC.

In this video Brad demonstrates that using a cap off of a refrigerant tank on a system can depress the Schrader core on the system in some cases. Make sure to use proper caps that have seals or brass flare cones.

Transcript

If you’re ever on a service call and you need to use a replacement valve cap, do not use the ones that are on the refrigerant tanks. Here’s a perfect example the one on the right is just a standard plastic cap you can see the circle o-ring in there the one on the left you can sort of see the dimple in the center it’s just got a flat piece of rubber across the bottom of the valve cap. What actually happens is where you see that depression is what’s pushing against the valve core. As you can see this is all oil and what’s happening is when they screw this on it depresses the valve cap and slowly leaks as you can probably hear. So that’s how this system lost its refrigerant charge, just make sure you’re using the proper caps make sure they have rings inside of them.
— Brad Hicks

Many of us are aware that X13 and Fully variable motor failure has peaked over the last few years and there are several reasons for that. One of the reasons is fairly simple and can be traced back to two simple installation and service practices that can be easily implemented.

  1. Seal all air handler / Furnace / Coil penetrations
  2. Use drip loops on wires entering the motor


Eliminating “Straws”

Straws are openings in the cabinet that are unsealed that “suck” moisture into the system and can cause condensation on the interior surfaces. These can be copper penetrations, drain port openings and electrical penetrations.

This is a bigger factor on fan coil systems and package units than it is on furnace/coil systems because in a fan coil or package unit warm/moist air can more easily be drawn in after the coil and before the blower.

When unconditioned air enters into the system due to these penetrations it can cause mold, short circuits, and corrosion. This moisture can also gather on wires and drip into electrical connections causing issues with motors and control panels.

Make sure to seal any penetrations into the conditioned compartments of equipment with proper rubber grommets or in some cases silicone or thumb gum can be used.


Wire Drip Loops 

Anytime a wire enters a plug, board or motor it is best to either locate the connection facing down to prevent water from entering or make a drip loop before the connection point. This allows moisture to drip off of the wire before entering the connector or device.

These issues have been identified as causes of X13 and ECM motor failure and checking these two areas can be very helpful in preventing future failure.

— Bryan

  

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I don’t do much in the way of “rack” refrigeration, but I recently had a conversation with experienced rack refrigeration tech Jeremy Smith and he got me thinking about EPR valves.

I’ve heard EPR (Evaporator pressure regulator) valves called suction regulators or hold back valves. In essence they hold back against the suction line to maintain a set evaporator evaporation or boiling temperature.

In refrigeration rack systems EPR valves play a vital role in ensuring that the product is cooled consistently and nearly constantly.

In an A/C system we have a TXV that maintains a constant superheat at the evaporator outlet. The evaporator temperature itself will fluctuate up and down depending on load.

In a refrigeration case you must first ensure you have full line of liquid using a sight glass or by checking subcooling. Then you make sure the case has proper airflow etc… then you set the EPR to maintain the proper coil evaporation temperature (by holding back pressure as needed) and then you check and / or set the TXV to the proper superheat. This ensures BOTH proper coil feeding as well as proper coil temperature.

Pretty cool right? (Pun intended)

— Bryan

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We have discussed DTD (Design Temperature Difference) quite a bit for air conditioning applications, but what about refrigeration? Let’s start by defining our terms again

Suction Saturation Temperature

Saturation temperature is the temperature the refrigerant will be at a given pressure if it is in the process of changing state. This change of state would be from liquid to vapor (boiling) in the case of the low side (evaporator / suction line). When we look at saturation temperatures instead of pressures we can use similar rules and we will see similar saturation temperatures across all refrigerants when the application is the same. Experienced HVAC and refrigeration techs pay far closer attention to the saturation temperatures than they do pressures.

Evaporator TD and DTD

Evaporator TD (temperature difference) is the measured difference between the suction saturation temperature (evaporator boiling temperature) and the box temperature. DTD (design temperature difference) is the designed or expected TD.

Delta T

Many A/C techs will confuse TD with Delta T. Delta T is the difference between the evaporator AIR temperature entering the coil to the air temperature leaving the coil. The Delta T will vary based on the humidity in the box where TD will not.

Target Box Temperature 

The temperature the refrigeration box should maintain when the system is operating properly

Superheat

The increase in temperature between the suction saturation temperature and the suction line temperature leaving the evaporator. Superheat is the temperature (sensible heat) gained between the point that all of the liquid boiled off in the evaporator coil and the suction line at the outlet of the coil. in refrigeration, like HVAC 10° of superheat  is average with a range from 3° to 12° depending on the equipment type (10° for med temp, 5° for low temp, 3° for ice machines ).

Hot Pull Down

Refrigeration equipment is unlike HVAC equipment in that the evaporator will spend most of its life running in a very stable environment with minimal fluctuation in the box temperature. 

On occasion a refrigeration system will see a huge change in load in cases where it was off and needs to “pull down” the temperature, or when doors are left open or when a large quantity of warm product is placed in the box. When a piece of refrigeration equipment is in hot pull down it cannot be expected to abide by the typical DTD or superheat rules and must be allowed to get near the design box temperature before fine adjustments are made to the charge, TXV superheat settings or to the EPR (Evaporator Pressure Regulator) if there is one.

Design Temperature Difference (DTD)

In air conditioning applications a 35° DTD is a good guideline for systems that run 400 CFM of air per ton of cooling (12,000 btu/hr). In refrigeration the DTD is much lower than in air conditioning. 

There are several reasons for this but one big reason is the desire to maintain relatively high relative humidity levels in refrigeration to keep from drying out and damaging product. Keep in mind that NOTHING is a substitute from manufacturer’s data but here are some good DTD guidelines for traditional / older refrigeration equipment. Keep in min dthat the trend is toward lower evaporator TD on newer equipment.

Walk-ins  10° DTD +/- 3°
Reach-ins  20° DTD +/- 5°
A/C 35° DTD +/- 5°

You then subtract the DTD from your box temperature / return temperature to calculate your target suction saturation. You can then use this target saturation / DTD and compare it to your actual measured saturation and DT once the box is within 5° – 10° of it’s target temperature to help you set your charge, TXV and EPR as well as diagnose potential airflow issues when compared with suction superheat and subcooling / clear site glass.

For Example –

If you have a medium temp walk-in cooler with a 35° box temperature you would expect to see a suction saturation of  25° +/- 3°

When doing a quick inspection of a piece of refrigeration equipment without gauges you can use this data to do the following calculation –

35° – 10° DT + 10° superheat = 35° suction line temperature +/- 3°

In this particular case logic tells us that the suction line could be no WARMER than 35° because that is the temperature of the air the refrigerant is transferring its heat to. However by the time you factor in the the accuracy of your box thermometer and line thermometer and the assumed saturation temperature you would still expect a 35° suction line temperature +/- 3°

For a -10° box, low temp reach-in you would calculate it this way

-10° – 20° DT + 5° superheat = -25° suction line temperature +/- 5°

Clearly, this is NOT the way to commision a new piece of equipment or to benchmark a system you haven’t worked on before, but it can give you a quick glimpse at the operation of a piece of refrigeration equipment without attaching gauges, especially on critically charged or sealed systems.

The best practice is to know the equipment you are working on, read up on it and properly log benchmark data the first time you work on a piece of equipment or during commissioning.

It should also be noted as Jeremy Smith pointed out, in recent years TD’s have been decreasing as manufacturers seek higher efficiency through higher suction and lower compression ratios. 

This means that TD’s as low as 5 can be designed into some units but keep in mind… the suction line can still be no warmer than the box so as DTD drops so does superheat and the critical nature of expansion valve operation.

— Bryan

 

 

Photo by Stephen Rardon

Whenever someone brings up undesired condensation on an air handler cabinet, or on a supply air duct or in a ventilation duct or on a vent like the one above, someone will inevitably say “condensation occurs where hot meets cold”.

Early on in my career, I believed this, so when I saw a vent like the one above I would either increase the air flow to warm up the supply air or I would seal around the vent or even pile insulation on top to make the ceiling “less warm”.

The trouble was, the problem almost never went away  just by trying to keep hot from cold

Then in 2003 – 2005 we had some of the most active hurricane seasons in Florida on record with numerous land strikes and tons of power outages as well as weeks with high latent (humidity load) and low sensible load (low outdoor temperatures).

condensation and mold growth EXPLODED

In the Summer of 2004 I had a few things happen that opened my eyes to the reality of condensation. 

First, I kept going back to the home of pro golfer and former Masters champion Mark O’Meara and wiping down his vents and ceiling all while frantically attempting to solve the root issue. 

Eventually, the vent DIRECTLY over his large, heavy, king sized bed started growing mildew. I tried moving it and it wouldn’t budge, so I ended up STANDING  on his bed, reaching with my tiptoes to wipe down the vent and the ceiling, PRAYING he didn’t walk in and see me that way. That event got me to the point where I understood that simply sealing the boot and vent and insulating above and around it wasn’t doing the trick.

Luckily a month or so later I was able to help participate in installing an Aprilaire whole home dehumidifier on a test house where they tracked the results vs. a typical home with a variable speed air conditioning system. 

The results were incredible, and the house with the dehumidifier had no issues with condensation and was able to maintain target relative humidity no matter the latent or sensible load on the space.

This is what I learned –

Condensation occurs whenever air hits dewpoint. Period.

Dew point is simply the temperature at and below which air containing a particular amount of moisture can no longer contain that moisture and will begin to give up water in the form of condensation. Saying dew point is the same as saying the 100% humidity point. 

Air can achieve dew point without coming into contact with a surface at all (see clouds), but often we observe that air hits dewpoint when it contacts a surface of a lower temperature than the air itself. So condensation on surfaces is a function of.

  • The moisture contact of the air
  • The temperature of the surface
  • Contact time on the surface

So what causes air to hit dew point and condensate in undesigned places? It is either colder or more humid than it is designed to be in those places.

Sweating Air Handlers

In Florida we have many air handlers (fan coils) located in unconditioned garages. This is not a great design right off the bat, and add in the fact that we ALSO have high latent (humidity) load so we run the blowers at low CFM output for and we have a recipe for sweating (condensating) air handlers.

The only way to resolve the issue is to warm up the air handler cabinet by running the system at higher CFM (warmer), Decrease the humidity in the garage through supplementary dehumidification (add a dehumidifier) or ventilate the area better which keeps the air in contact with the cold air handler surface for a shorter period of time.

Supply Register Condensation

Common knowledge about sweating vents tells us that when a vent sweats it should be sealed. This is true, because it is just a good practice, but also because it prevents unconditioned, moist air from entering in around the boot or can and condensing moisture around the vent and on the ceiling. In my experience sweating registers are more often caused by high humidity in the space, poor air velocity, low air temperature caused by low system CFM output or a combination of all three. 

The problem is that many techs will try to solve this by increasing system airflow. While increasing air flow will increase the register temperature it will also reduce the ability of the system to dehumidify resulting in high relative humidity in the space.
The best way to reduce sweating registers is to reduce or eliminate the effects of moisture “drivers” that introduce new moisture into the space in the first place. This can be done by properly ventilating bathrooms and kitchens, keeping doors and windows shut, improving the air tightness of the conditioned space and using and ERV to keep the space under neutral or slight positive pressure.

Obviously proper Cooling system sizing and duct design will help extend system run times and decrease indoor humidity.

It is also helpful when designing fresh air systems in humid climates to only provide the amount of fresh air required and no more unless an enthalpy control system is in place.

It can also help to redesign registers and branch ducts to output the designed face velocity of the vent for better air mixing in the room. In extreme cases, supplementary dehumidification can be added to stop the issue once and for all.

Duct Condensation 

Ventilation ducts will often condense moisture on the inside when they are routed through spaces that will often be cooler than the air contained inside. This is why it is a good practice to insulate ventilation ducts in most climates unless the duct is run completely in the conditioned space.

Supply air ducts will also condensate at times on the outside when one of the following situations occur –

  • The air in the duct is colder than designed
  • The insulation of the duct is insufficient
  • The insulation of the duct is compressed
  • The ventilation around the duct is poor (some ducts are designed to be buried in insulation and others are not)
  • The moisture content around the duct is high

Usually, when you find condensation on ductwork it is a combination of two or more of these issues.

All of the issues discussed above can usually be prevented by –

  • Proper ventilation of moisture laden air (bathrooms, kitchens)
  • Better sealing of conditioned spaces
  • Better insulation of conditioned spaces and “cold” objects
  • Proper duct design and system air flow output
  • Keeping ducts and air handlers inside the conditioned envelope when possible
  • Placing vapor barriers on the “warm” side of structures to prevent moisture intrusion
  • Use of ERVs to positively pressurize the space (In very warm climates) and neutral in multi season and cold climates
  • Installation of supplementary dehumidification when required
  • Keep the space no cooler than it must be for comfort
  • Size cooling equipment properly to extend run times and reduce space humidity
  • Do not bring in excessive fresh air during humid outdoor conditions

— Bryan

 

 

 

I knew a tech when I was just starting who was hands down, no questions asked, the best technician at the company I worked. 

EVERYONE, we are talking over 60 techs… we all knew it.

His name was Mike Gilford 

Being the little brown nosing ladder climber I was, I made a complete study of mike and found three things about him.

#1 – He read stuff. When a new product came out he would read up on it, data tags, product data, bulletins etc…

#2 – He didn’t talk much. There was no need. He proved what he knew by what he did more than what he said.

#3 – This is the big one. This is the one that I am confident is the trait that made him who he was. He was humble, willing to be wrong and willing to learn.

Let that sink in a minute…

Sure Mike had an ego like we all do. He didn’t like being corrected and he wanted to do things right.

But…

He never let his ego get in the way of growing and learning

If you had something to share that would benefit him and others, he kept an open mind and was willing to accept it.

That’s a hard pill to swallow.

I knew Mike when I was in my early twenties and I haven’t seen in over 12 years but I vividly remember things he taught me.

I still want to be like Mike.

— Bryan


Condensate overflow prevention devices or float switches as they are often called are such simple devices that you wouldn’t think there would be much room for controversy. In my experience there are few areas of the trade where technician and installer preferences and opinions vary greatly.

Let’s start with some float switch basics

Float (condensate) switches are designed so that they will remain closed when water is going down the drain like it’s supposed to and then open when an overflow condition occurs. In order for the switch to open it must be positioned in a location that is dry normally and will reliably fill with water when a drainage issue occurs.

There are very simple switches that just clip onto the edge of primary or secondary drain pans like the Rectorseal Safe-T-Switch SS3 shown above. When the primary drain overfills it begins leaking into the secondary pan below and a pan sitch like the SS3 will open when the water levels rise. This type of switch can also be used in the primary pan so that it only trips when when the water level exceeds the normal levels. In both of these cases it is important that the switch is firmly mounted and level so that it will function as designed when the time comes.

Then there are the more typical devices like the Safe-T-Switch SS1 and SS2 that are designed to be installed to an aux drain port or sometimes even in the primary drain. When it comes to the mechanical code, there is no “nationally adopted code” but most states and localities adopt the International Mechanical Code (IMC) is the most widely adopted code in the country and it states a few things that are important to consider in addition to the general requirements stating that an overflow device is required.

307.2.3.1: “On downflow units and all other coils that do not have a secondary drain or provisions to install a secondary or auxiliary drain pan, a water-level monitoring device shall be installed inside the primary drain pan. This device shall shut off the equipment served in the event that the primary drain becomes restricted. Devices installed in the drain line shall not be permitted.

307.2.5: “Condensate drain lines shall be configured to allow the clearing of blockages and performance of maintenance without having to cut the line.”

So while this may not apply to you depending on where you live, in general the code says –

  1. You need to have overflow protection
  2. It needs to be in a secondary pan, in an overflow drain or in the primary pan UNLESS the unit also has an aux drain line that drains outside or a secondary pan under it. 
  3. The primary drain needs to have some sort of cleanout that doesn’t require taking the drain apart

While there are cases where installing in the main drain is permitted the cases are limited and there is also the issue of buildup collecting on the float itself when it is installed in the main drain. While some technicians swear by the practice of putting the float switch in the main drain line I generally advise against it.


So in most upflow applications we will be installing the condensate switch to the aux port on the evaporator coil. When installing the switch you want to set in such a way that you accomplish the following –

  1. The float trips (rises) before the pan overflows
  2. Have free access to the access panels and filter door
  3. Water should flow freely to the float if an overflow occurs
  4. The float is installed level so it can rise and fall freely 
  5. The switch is installed so that it cannot be easily moved into an improper position 

Many technicians swear that if the aux drain is pitched down that water will flow into the float all the time and they pull the drain perfectly level or even pitched upwards. Others swear that the switch must be mounted directly to the front of the unit. The truth is that so long as you follow  the 4 rules above the float could be positioned in many different locations. It is not the orientation of the pvc connected to the aux port that holds back the water, it is the level of the aux port opening that does that. The level that the water must rise and the total depth of the primary pan varies from model to model. This means that in some cases a practice that works just fine on one brand may not on another.


Many contractors have found that installing a float switch with a flat bottom like the SS2 right on the front of some shallow coils can result in the pans overflowing before the float trips. Others have found that this same practice can result in difficulty accessing air filters. In these cases it may make sense to route the aux drain around to the side, pitch the drain down and level it out with 45s and install the switch there. Like all drains it must be pitched slightly down for the water to reliably reach it’s destination, but the switch itself should still be installed level.

Once again, this practice does not result in false tripping because it is the level of the aux drain port that holds back the water, not the pitch of the drain (unless the drain is improperly pitched upward).

Finally, there is a dispute over whether to break the “R” circuit or the “Y” circuit with the switch. It is generally recognized that breaking R is a better practice to prevent short cycling unless the system has another dedicated method for condensate switch connection.

— Bryan


The title says it all. It should be one of the first things you learn when you started… however, I have seen a lot of experienced techs who seldom (if ever) do it.

When connecting to a tank… purge your hose by cracking the center connection at the manifold for a second.

When connecting to a system, crack each connector for a second and then tighten. (Unless you are using ball valves or low loss of the same refrigerant type).

Low loss brings up a different subject. If you are using them, you need to make sure not to switch between refrigerants without recovering all the refrigerant from your gauges .

Both air and incorrect refrigerant are not acceptable to add to the system… even in small quantities.

— Bryan

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