If you are primarily a residential technician working on equipment under 5 tons, there are a lot of similarities between the systems you are used to and 5 – 20 ton rooftop units that are common to the light commercial market. There are MANY additional things to consider on larger equipment and here are just a few. Wash Fresh Air Filters While fresh air intake is becoming more common across the entire industry, it has been most common in commercial environments. Fresh air filters are often metal mesh and should be washed regularly with a hose and maybe some degreaser when they are in an environment near exhaust hoods. Check and Adjust Belt Tension When I was a new commercial maintenance tech I used to get belts far too tight. This would result in high amperage on the blower, belt breakage, stretching and excessive bearing wear. You want the belt to be tight enough that it doesn’t slip or vibrate excessively but no tighter. In most cases, the tension is adjusted by moving the position of the motor itself, either by way of adjusting the height of the motor base plate or sliding the base plate back and forth. In some cases, the tensioning will be done with a tensioner pulley like the one shown below. Many techs will use the 1/2″ deflection rule or something similar to guess at belt tension. The trouble is this rule doesn’t account for the length of the belt or the amount of pressure used for deflection. Many experienced techs have a good “feel” for proper belt tension, but even that can be pretty far off at times.
Browning makes a belt tension tool that you can use to ensure that the best has the proper tension for the application. Here is a quick video showing how it works. You can read the full guide on using the tool as well as proper deflection force HERE Keep in mind that belts do need to be replaced regularly. If a belt begins to loosen significantly due to stretching after the initial break-in period, it is often best to replace it rather than to keep tightening it. Align Pulleys When aligning pulleys keep in mind that you need to align the pulley centers with one another both right to left as well as the “camber” or angle of the pulleys themselves. Often pulley misalignment can happen when one of the bolts holding the motor base in place begins to slip or if a pulley has been adjusted or replaced. Misaligned pulleys and result in thrown or damaged belts, damaged bearings and noise. In addition to aligning pulleys, keep in mind that pulleys can become worn over time and lose their designed shape or wear grooves in the sides. If a pully becomes worn it will lead to improper airflow, noise and shorter belt life. Clean Condensers, Split as Needed Many commercial units have multirow condensers that will need to be split from time to time to get them completely clean. The frequency that this will be required is dependant on the location of the unit and the amount of debris in the air. Here is a video showing the process. Checking Phase Balance Many 3-phase systems will already have phase monitoring controls installed that check for voltage imbalance and dropped legs of power. This is important on 3-phase systems because even small imbalances can result in motor heat and failure. Check voltage from leg to leg on all three legs on the equipment. Any imbalance of more than 2% is considered detrimental and an imbalance of over 4% is totally unacceptable. To learn more about exactly how to measure voltage imbalance read this excellent article by John Tomczyk — Bryan