Do You Own a Backup Wrench?

I am often talking about new technology and recent trends in HVACR on this blog. Today I would like to discuss a rather old piece of technology – the backup wrench. If you work in mechanical trades and you don’t own a backup wrench, then you are my intended audience! A backup wrench is not used to reverse anything, and it does not have left handed threads. Backup wrenches are often specified by manufacturers when installing mechanical fittings, yet most techs do not have any wrenches in their tool box named a backup wrench. I have sometimes reminded students to use a backup wrench only to be told that they only have some open end wrenches and a couple of adjustable jaw wrenches – no backup wrenches. By now you hopefully have figured out I am pulling your leg. “Backup” does not describe a particular wrench, but how the wrench is used. The wrench is backing up the fixed part, keeping it from turning. When tightening a nut or fitting onto a valve or coil, you are often instructed to use a backup wrench. Many units have stickers on them stating: “use a backup wrench.” The backup wrench holds the fixed part in place, keeping it from twisting when the nut is tightened. Otherwise, it is quite possible to turn the fixed part once the nut is tight. This twists the copper tubing connected to the valve or coil connection, causing leaks and restrictions. Unfortunately, this is a common occurrence in school. Students try to “fix” a leaky flare with a 12” wrench and a hefty turn. Repairing the damage can be pretty tricky, and it is definitely time consuming. If you look carefully, most male flare connections have flats on them – that is where the backup wrench goes. One wrench goes on the fixed part and another goes on the part that is turning. That way you can control exactly what gets turned. So the next time you go to tighten a flare on a valve or coil, make sure to use a backup wrench. If you don’t have a backup wrench, send me $50 and I will send you one with instructions for using it.

Appearance Counts!

I recently attended a meeting with contractors and instructors. We are looking for a way to help local contractors hire, develop and retain the technicians they need. More than one contractor said that lack of technicians was hindering their company’s growth potential. Contractors were looking for a way to pump more lifeblood into our industry. The instructors in the meeting were trying to find out what  we could do to more effectively meet their needs. This involved trying to identify the most crucial aspects that seem to be missing from much of today’s prospective talent. The first thing mentioned was personal appearance. As one contractor put it “if I can’t send you to my grandmother’s house, I can’t hire you!” They discussed job applicants with body piercings, tattoos, even applicants wearing spiky dog collars! It may be narrow minded and prejudicial to assume someone wearing a spiky dog collar is not trustworthy, but I believe much of the general public would feel uneasy about letting someone into their house who was wearing a spiky dog collar. Service Techs ARE the company as far as the customer is concerned. The impression they make has a lot to do with the trust the customer places in them. If the customer does not trust them, they will be hard pressed to do their job – the customer will be suspicious of anything they say or do. If you want to pursue a career dealing with the public, you need to carefully consider the impact any body art may have on people who meet you. Often, body art almost seems to scream “I WANT TO SHOCK YOU!” Even companies that are desperate for help don’t want that association with their company. Here is a short list of things that will improve your chances of getting past the first interview.
 

• Before going to the interview cover up any tattoos you can and remove any extraneous metal objects from your body that might be seen during the interview. 
• Don’t wear a T-shirt with an obnoxious logo – wear a shirt with a collar. 
• Turn your phone off before going in.  
• Don’t drop the F bomb in every sentence – in fact, don’t curse at all. If you are used to throwing one or two expletives in every sentence you had better practice talking at home for a while. Speech becomes habit. Try going the whole day without cursing the day before the interview.
• Look the interviewer in the eyes when you talk – don’t look at the floor or up at the ceiling.
• Smile –nobody wants to work around a grouch.
• Before the interview you should study HVACR so you know how to talk intelligently about the field you are pursuing.

Tracing a Communications Problem

One bad apple don’t spoil the whole bunch girl …
You may know the Jackson Five hit that line comes from.
(The first time I heard it was NOT on an oldies radio station.)  Unfortunately, when it comes to communicating controls, one bad communicating board CAN take down the whole network. If the communicating portion of a board is sufficiently damaged, it can prevent communication to ANY of the components on the communicating network. This is because they are all tied together in parallel. A sufficiently low resistance can pull down all communication signals on the whole bus. We saw this first hand this week in our lab. A system that had been operating correctly started having problems communicating. A lab instructor had put in a problem and the student tried to troubleshoot by swapping wires around, resulting in a dead board. (In my experience, swapping around wires just to see what will happen almost never ends well!) Now, the ENTIRE SYSTEM stopped communicating and the control could not find the furnace, which did not have any problems. When the communicating wires to the condensing unit were disconnected, the thermostat found the furnace and was able to operate it. The bad condensing unit board managed to pull down the entire communication bus. When you have a communicating control system that will not communicate, the first step should always be to check your connections. Make sure they are correct and making good contact. Then, try to isolate different parts of the system by connecting one part of the system at a time to the communication bus and seeing which specific component will not communicate. Unlike standard 24 volt controls, you cannot read a voltage to determine if a board is communicating. Isolating the components and checking them individually usually identifies the component which is causing the problem.

Understanding Pressure Gauge Specifications.

Pressure gauges have many specifications which technicians should understand when selecting a gauge, including range, resolution, accuracy, proof pressure, and burst pressure.

The range is the lowest to highest reading on the gauge. It is important that the range of a gauge fit the pressures for which it will be used. You want a gauge able to read the highest pressure you might encounter, but you don’t want the top reading much higher than that. This is because accuracy is stated as a percentage of full scale. A gauge with an accuracy of 1% and a top reading of 300 psig has a possible error of 3 psi. If you make the top reading 600 psig, now the possible error becomes 6 psi. If the pressures you will be reading only go up to 250 psig, expanding the top pressure reading just makes the error larger.

Resolution is the smallest indication the gauge can display. A gauge that can display in tenths of a pound has a resolution of 0.1 psi. This is not the same as the accuracy. Just because a gauge CAN display in tenths of a pound does not mean the reading is accurate to tenths of a pound. However, having a small resolution does make the gauge more useful for precise readings than another gauge with the same accuracy and top scale. For example, there are both analog and digital gauges with the same accuracy, but an analog gauge with a scale of 0 – 500 psig cannot have a resolution in tenths of a pound – there is just not enough space. A digital gauge with the same accuracy and top reading has no problem displaying in tenths of a pound.

Accuracy is stated as plus or minus a percentage of full scale. Full scale is the highest reading on the gauge. To determine how far off a gauge can be and still be within specifications, multiply the percentage accuracy times the top reading. For example, a gauge with 1% accuracy and a top reading of 500 psig would have an accuracy of plus or minus 5 psi. Note that the accuracy is plus or minus a percentage of full scale, NOT, a percentage of the reading. For example, a reading of 400 psig could indicate a pressure anywhere from 395 psig to 405 psig. This is not too bad at 400 psig, where 5 psi only represents 1.25% of the actual reading. However, plus or minus 5 psi becomes a problem at lower readings. A reading of 25 psig could indicate a pressure anywhere from 20 psig to 30 psig.  Now 5 psi represents 20% of the actual reading. For accuracy reasons, you don’t want the top reading on a gauge to be any higher than it has to be to get the job done.

Temperature compensation is an important aspect of accuracy in digital gauges. The accuracy of the sensors used in digital gauges changes with temperature. A gauge that specifies an accuracy at a single temperature is only that accurate at that temperature. It will be less accurate at other temperatures. A temperature compensated gauge maintains its accuracy over a wider range of temperatures. The most accurate digital gauges will be temperature compensated.

Proof pressure is the highest pressure the gauge can withstand without damaging the sensor. This is typically considerably higher than the highest reading.

Burst pressure is the pressure at which something on the gauge physically breaks. It is higher than the proof pressure. Gauges should be selected with proof pressures and burst pressures considerably higher than the highest pressure you would expect to encounter. A gauge which would be perfectly acceptable for use with systems using R-134a might not be acceptable for use on systems using R-410a.