Motor Rotation

Many single phase motors can only turn in one direction. For example, pump motors and fan motors. Since the pumps and fans they operate only work in one direction, the motors that drive them re usually built for one direction.  This can pose a problem for service techs when replacing these motors. Often, service motors solve this problem by being reversible. However, OEM replacement motors are generally not reversible, so you must specify the correct motor rotation. To do this you need to understand the terminology that is used to describe motor direction.

There are only two possible rotations: clockwise and counter-clockwise. However, there are also two perspectives: looking at the shaft end of the motor or looking at the lead end (opposite the shaft end). A motor which turns clockwise looking at the shaft end is turning counter-clockwise when viewed from the lead end! The point is that just stating a direction is not good enough. You must also identify a perspective.

There are several names for the two possible perspectives. The most common are shaft end and lead end. The shaft end can also be called the output end, drives end, or pulley end. The lead end is sometimes referred to by placing “opposite” in front of whatever phrase is used to describe the shaft end; such as, “opposite drive end.”

Normally these descriptions are abbreviated, which tends to add to the confusion. Below is  list of some of the abbreviation used. The graphic above each group uses an arrow to show the rotation looking at the motor shaft.

CCWSE Counterclockwise shaft end
CCWOE Counterclockwise output end
CCWDE Counterclockwise drive end
CCWPE Counterclockwise pulley end
CWLE   Clockwise lead end


CWSE  Clockwise  shaft end
CWOE Clockwise output end
CWDE Clockwise drive end
CWPE Clockwise pulley end
CCWLE Counterclockwise lead end

Clockwise and Counter-Clockwise

Many folks have heard the phrase “righty tighty, lefty loosey.” This little limerick is a clever way of remembering which way traditional right-handed threads turn. However, it can be misleading. The right or left direction refers to the direction the top of the circle will turn. But the bottom of the circle turns in the opposite direction. So while the top is being turned to the right, the bottom is being turned to the left.

CLOCKWISE

COUNTER-CLOCKWISE

I really prefer the terms clockwise and counter-clockwise to describe rotational movement because you don’t have to be concerned if you’ re looking at the top of the circle or the bottom. You only have to remember which way a clock hand moves. Therein lies the problem. In today’s digital age, some people can’t tell you which way a clock hand moves because they rarely see one.

Every program should have an operating analog clock in the class room so students can learn the difference between clockwise and counterclockwise. Notice how the numbers on the clock face progress from the top to the right, creating clockwise motion. Logically, counter-clockwise motion is the opposite.

LEFT HAND THREAD ON ACETYLENE HOSE

This little saying also ignores the left handed threads, which are exactly backwards from right-hand threads. Although far less common, left hand threads are often found on connections for flammable gas, such as the regulators and hoses used for Acetylene on an oxy-acetylene torch. In that case it is “righty loose, lefty tighty.” Doesn’t have quite the same ring to it. Left hand threads on torches have a hash mark on them to indicate that they are left-hand threads. The acetylene and oxygen have opposite threads for a reason – to prevent mixing up the regulators and hoses. Mixing the gasses under pressure can create a combustible mixture.

Intelligent Controls Improve System Charging

"Charge View" by Johnson Controls

Units with intelligent boards that assist in system charging are available. Many VRF systems can assist technicians in charging the unit. They are so complex that some type of automated assistance is really necessary. With multiple heads and variable capacity compressors there is really no way to use system pressures to determine the correct charge. Computer assistance is available through installation and charging applications that run on laptop computers, to evacuation and charging modes built into the system controls.

Trane introduced split system units with “Charge-Assist” back in 2008 in their Xli line. These systems have pressure transducers and temperature thermistors which are used to operate the electronic expansion valves in the unit. The board can also use the input from these sensors to determine if the system charge is correct. An external  “Charge Assist” solenoid can be controlled by the board to allow the unit to charge itself. On these units, the technician only sees a blinking LED on the unit control board.

Johnson Controls (York, Coleman, Luxaire) are now offering units with built in pressure and temperature monitors and a screen to display system pressures, liquid line temperature, suction line temperature, superheat, and subcooling. The system will also tell you if it is correctly charged. It is like having a digital gauge set built into the unit. The main point is that you can check the unit charge without attaching any gauges or temperature probes. That means you will not lose any refrigerant while checking the charge.

These examples represent only the very high end systems from a few different manufacturers, but I believe it shows the direction the industry is headed. Systems will have sensors and intelligent controls monitoring system operation. I am sure that as the technology matures, its cost will come down, making this technology attractive to other manufacturers and in more main line units. Another driving force will be the desire to insure actual equipment performance and efficiency match the design. The most efficient system available installed incorrectly may perform worse than the lowest builder grade equipment available. Designing intelligent controls into a system is a way to improve system installation and service by taking guesswork out of charging. With systems employing these intelligent controls you really have no excuse for leaving the unit improperly charged.