Month: May 2017

My technician (and brother in law) Bert made a good point the day (It’s hard for me to admit it, but it’s true). When he needs to open the refrigerant circuit to make a repair regardless of whether he is recovering or pumping down, he pulls out his nitrogen tank and his regulator (We like the VN500 shown above).

Once the refrigerant has been pumped down or recovered, instead of opening the system to the atmosphere and exposing it to air and moisture, he simply puts it on “BRZ” mode and introduces a very low flow of nitrogen. Now when he cuts into the system to replace a line drier, or a coil, or a compressor, or an accumulator (you get the idea) the system will stay dry and it will be less likely that anything undesirable enters the system. You simply connect the regulator to your center hose and direct the flow to the high side, low side or both depending on what part of the system you have open.

Once the system is all dry fit into place you are then ready to flow nitrogen while brazing, pressure test and even triple evacuate if nitrogen is needed for that.

The biggest hurdle to getting techs to flow nitrogen while brazing is getting the nitrogen tank off the truck. If you get in the habit of connecting nitrogen before you ever cut or open the lines it even further reduces the chance that you “forget” and increases the chances that your system is clean and dry.

Just a thought (from Bert)

— 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, concentric flaring tool with a 45-degree cone and block. 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.
  • 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.

— Bryan

 

Look closely at a contactor on your truck and you may find some interesting ratings you never noticed. Things like terminal ambient temperature ratings and torque specs. One reading you may overlook is the RES AMPACITY of the contactor or relay. The RES rating is the RESISTIVE LOAD AMPACITY (amperage capacity) or rating.

Remember, a contactor and relay is both a switch (contacts) and a load (coil) that controls the switch (contacts). The FLA, RES and LRA are the ratings of the switch / contacts / points portion of the relay / contactor, not the coil portion. The coil is just rated for voltage and cycle rate (hz).

You will notice that the RES (Resistive load) rating is higher than the  FLA (Full Load Amperage) rating and much lower than the LRA (Locked Rotor Amperage) rating. So the contactor above the contactor above would be sufficient to control / switch a 40 amp full load INDUCTIVE load and a 50 amp RESISTIVE load.

So what is the difference between an inductive and a resistive load?

An inductive load is a magnetic load that converts electrical energy into kinetic energy (motion) through electromagnetic force (magnetism). This would usually be motors and solenoids in HVAC/R, really anything where magnetism and motion are involved (Transformers and inductive rages being examples of induction WITHOUT motion for the purist).

An inductive load will experience a spike in current when voltage (potential) is first applied, this is called locked rotor amps (LRA) because it is the current a motor will draw when it starts up from a locked or stalled position.

A Resistive load is a a load that converts electrical energy directly to light or heat as the electrons flow through a resistive conductive path. These would be things like heat strips, crankcase heaters and incandescent light bulbs. Resistive loads do not have any internal variation in load and the voltage and amperage are completely in phase. This means that when a contactor, switch or relay are controlling a resistive load there will be less load variation.

The conclusion is that often contactors and relays can handle a higher amperage across the contacts when the load is resistive (Light / Heat)  than when it is inductive (Motor / Motion).

— Bryan

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