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.