Random Puzzle Assembly

Many students trying to troubleshoot HVACR systems have difficulty navigating the sheer amount of data one can collect. If you go about just collecting a lot of data, it does not take very long to confuse yourself. I often see people taking resistance, voltage, and current readings on just about every conceivable location on the system without having a clear idea why they are taking the readings. This is like trying to build a 1000 piece jigsaw puzzle by just randomly trying to fit pieces together without looking at the shapes or color patterns on the pieces. When building puzzles, it helps to have a plan. There are different plans – outside edges first, organizing pieces by color, or organizing pieces by shape, but having a plan improves your chances of success. Troubleshooting is the same way. You should have a plan to organize your data collection into something meaningful. You should know why you are taking a voltage, resistance, or current reading before taking the reading. Ideally, each measurement you make should eliminate an area of inquiry. A simple example is checking the power supply to the unit. If you read the correct incoming voltage, you can eliminate that as a source of the problem. But if you don’t read the correct voltage at the power supply, then there is no need to check anything inside the unit until you have solved the power supply problem. There are probably as many systems as there are technicians. It is not too important what your system is, so long as it is based on an understanding of how the equipment functions and proceeds logically. For a non-functioning component, I generally want to know if that component is receiving the correct voltage. If it is, then I need to take a closer look at the component. Otherwise, I need to check the circuit that supplies voltage to the component. Many technicians check the line voltage and control voltage first. This does not take long and covers a large number of problems. Another technique is to start at the thermostat and work towards the non-functioning component until you find a break in the circuit, or eventually reach the component. The key point is that each piece of data you collect should tell you something. This will allow you to take far fewer readings and isolate the problem much faster.

Are You Seeing Ghosts?

Have you ever taken a voltage reading with a digital meter and gotten something that really did not quite make sense? With high impedance digital meters, it is common to get readings where you don’t expect them. This can be very confusing for students. Volt-meters are basically electrical loads. Normally, for them to read anything, they have to be in a complete circuit. The impedance rating of a meter determines the amount of current required to operate the meter. The higher the impedance, the less current required to operate the meter and get a reading. High impedance meters are preferred for electronic work because they don’t add any load to the circuit they are testing. However, high impedance meters can behave differently from older analog meters. A phenomenon called capacitive coupling can cause high impedance meters to read voltages that low impedance meters don’t read. These voltages are sometimes referred to as ghost voltages. Unenergized wires and devices in close physical proximity to energized wires and devices are charged by the energized wires in their proximity. This is a static voltage which cannot move any appreciable current. Since high impedance digital meters really don’t require a current flow to operate, they can read the ghost voltage. To differentiate between a ghost voltage caused by capacitive coupling and a hard voltage that will move current, place a load across the voltage. When loaded, a ghost voltage disappears. Some digital meters actually have settings for both high and low impedance to allow technicians to distinguish between a ghost voltage and a hard voltage. Fluke makes an adapter, SV225,  that can be used with high impedance meters to effectively turn them into low impedance meters by placing a small load across the leads. Low impedance analog meters do require a small current to operate, so they typically will not read the ghost voltage built up by capacitive coupling. 

Checking ECM Motors

Electronically Commutated Motors (ECM) are pretty common these days. You can’t troubleshoot them the same way you do a standard PSC motor. The ECM motor is really two components – a motor and a control module. One big difference in checking these motors is that is that they receive voltage all the time, not just when the motor is operating. Really, it is the module that is powered all the time – the module then controls when the motor receives power. The first thing you want to establish is if the problem is in the controls to the motor/module, or the motor/module itself. A device called a TECINSPECT helps you do this. Turn off power to the unit. This step is important, not just for your safety, but for the motor’s safety. Unplugging connectors from the motor while the unit is powered up can cause the module to arc out. Unplug the control plug from the module and connect the TECINSPECT. Connect the two tecmate alligator clips to 24 volts, such as the R and C terminals. Turn power back on to the unit. The LED on the TECINSPECT should light to show it is receiving 24 volts. Flip the TECINSPECT switch on and the motor should operate. If it does, the problem is in the control board or wiring harness from the unit. If the motor does not operate, the problem is in the motor or module. If the problem is in the motor or module, the odds are that it is the module. Turn the power to the unit back off and wait 5 minutes for the high voltage capacitors inside the module to discharge. Remove the module and unplug it from the motor. Ohm out the motor. The resistance between any two of the three motor leads should be approximately 5 ohms. If the readings check out, the problem is in the module. You must replace the module with one designed for that specific unit because the mmodules are programmed for the blowers they control.  

Courage

Monday, May 20, 2013
The teachers in Moore Oklahoma teach a lesson in courage.

The Air First Pledge

I want you to take the “air first” pledge. “I solemnly swear to check the system airflow before I connect my gauges.” If the system airflow is off, the pressures are going to be wrong, so there is no point in connecting your gauges until you know that both the evaporator and condenser are clean and the correct amount of air is moving through each of them. No amount of refrigerant can correct for a dirty air filter, you have to change the filter. I understand that not everyone in the air conditioning business has a tool for measuring airflow. But we are in the AIR conditioning business! Would you trust an electrician who worked without a volt meter? You don’t have to have a flow hood to measure airflow. There are several tools under $300 that do a good job. You can get a Fieldpiece hot wire anemometer, several companies make reasonably priced digital manometers, there are many inexpensive rotary vane anemometers, or you can get a Magnehelic gauge for less than $100. Dwyer sells an airflow meter for less than $50 that reads both velocity and inches of water column pressure. It is not in the same class as the other tools mentioned, but it is a whole lot better than nothing. Why should you invest in a tool that you have been doing without? For one, customers notice when you use instruments instead of guessing. But the best reason is because it makes your job easier. It is always easier to solve problems if you have good data, which you can’t get by holding your hand over the register. How many times have you added refrigerant to a system only to discover later that the coil was plugged up with cat hair? Wouldn’t it have been easier to check the airflow first and correct the real problem? Even if I can’t convince you to start measuring airflow, please at least check the air  filter and check out the airflow with your handomometer before pumping refrigerant into a system that does not need it. Take the air first pledge! 

The Perfect Mothers Day Gift

Nobody is more interested in your success than your mother is. Not even you. Mothers pour their heart, soul, blood, sweat, and tears into insuring their children are successful. Go to any school honors day, any event celebrating achievement, or any graduation and the happiest people there are mothers. Mothers usually also make up the largest part of the audience at these events. Oh, there are plenty of fathers too, but there are more mothers and they are clearly more involved with the program. After all, who made you do your homework, shuttled you back and forth to band practice, and waited for you for hours at your different events? Your mother. Who packed your lunch, made you dinner every night, and cleaned up after you? Your mother. Who made sure you registered for the SAT and ACT on time, made sure you got your college applications done on time, and made certain that you dotted every I and crossed every T on every application? Your mother. I could go on, but I believe you see the point – your mother has more time and energy  invested in your success that you do. That is why your success is the ultimate mother’s day gift. More than anything you can give her, she wants to see the fruits of her labor lead to a happy and successful life for her children. So Mom, I am happy, healthy, and financially successful. Truly, I have received many blessings in my life, but first and foremost, I was blessed with a great mother. 

The Hand-O-Mometer

Most technician’s favorite instrument is the hand-o-mometer. They use it to measure air temperature, suction line temperature, liquid line temperature, air velocity, and airflow. A few even use their hand-o-mometer to measure voltage, although that is not recommended as it can fry the microprocessor. Yes, we grab the suction line to see if it is cold, we grab the liquid line to see if it is warm, we hold our hand over air outlets to see if we have good airflow. At times it seems like we are trying to heal the system by laying on of hands. I must admit, I do it too. I feel compelled to touch the unit. We are like Thomas – unless we put our hands on the suction line and in the air-stream, we will not believe. The problem is that hand-o-mometers take decades to calibrate. In truth, even the most experienced hand-o-mometer is just not very accurate at any of these readings. We can say that the fan is blowing, the unit is cooling, or the unit is heating using our hand-o-mometer. However, we can’t say for certain that a system is performing the way it should just because the suction line is cold and the air leaving the registers feels good. In the era of high energy costs and increased awareness of system efficiency, this is simply not good enough. Employers and customers are demanding accurate measurements – not just rough approximations.

The idea is to use accurate measuring instruments to take system operational data and compare the data with a standard provided by the equipment manufacturer or system designer. Then if the data does not fall within specified parameters, we analyze the cause, make adjustments, and take new measurements. I believe this takes three things: accurate instruments to take the measurements, a good understanding of how the system works, and the patience to perform service work correctly. In the end, you will save time doing things once the right way, instead of several "close enough" attempts. Brian Baker has suggested a phrase to me that sums this all up

“Diagnostic analysis is the rule, so use proper tools”

So my suggestion is that we start using accurate instruments to perform diagnostic analysis and use our hands for more important things, like holding a cold beverage at the end of the day or hugging our wife and kids.