EC Indoor Blower Motors, Resistance is Futile

Part one of this three-part series on indoor blower ECMs provides information on power connections and airflow adjustment. Thirty-two years after ECM (electronically commutated motor) technology was introduced to the residential and light commercial HVAC industry, the indoor blower motor segment of this industry is now almost completely converted from PSC to ECM. Interestingly enough, the first application for ECM in the HVAC industry was also the indoor blower motor. The constant airflow “variable speed” indoor blower motor was introduced by GE* in 1987.

This motor is primarily applied to top tier multi-stage or modulating HVAC equipment. By 2005, approximate 15% of all new HVAC equipment was built with this motor. However, in 2006, there was a major shift in this segment driven by the 13 SEER regulation. At the same time this regulation was being developed, Regal Rexnord Corp. (“Regal Rexnord”)¹ was developing a new type of ECM for indoor blower motor applications called “constant torque.” This technology would provide the same electrical efficiency as the constant airflow ECM but with fewer features and a lower cost.

The constant torque ECMs would be utilized by almost all HVAC OEM in the majority of their air handlers and package systems that moved from 10 SEER to 13 SEER in 2006. By the end of 2006 over 50% of new HVAC equipment was built with an ECM indoor blower motor. In 2019, another regulation focused on the electrical efficiency of fossil fuel appliances has again caused a major shift in this segment. Due to the Fan Energy Rating (FER) regulation that went into effect July 2019, the vast majority of furnaces that were still being built with PSC motors, are now built with constant torque ECMs.

So, it seems like now would be a good time for a refresher course on these two types of motors. Even though they are both built with ECM technology, they are very different in almost every aspect. This article will cover the basic design, input connections and airflow adjustment of each type of motor.

Constant airflow ECMs

Let’s start with the constant airflow (often referred to as “variable speed”) ECMs. I refer to these motors as “communicated ECMs.” The term “communicated” here refers to any type of communication between the HVACR system control and the motor control that meets the following criteria:

• The connections are fixed at both ends (typically with plug connections), meaning that they are not adjusted from one position to another to modify the operation of the ECM.
• Airflow adjustments related to the output of the motor are selected at the HVACR system control or user interface.
• The line-voltage inputs are separate from the communication inputs and are powered continuously from the HVAC system.

Figure 1 shows the type of plug connections used by Genteq^® constant airflow ECMs.

The HVAC system manufacturer provides charts (often labeled as “set-up” or “airflow” or “comfort” settings) that relate the position of each switch or jumper to its corresponding setting. In some cases, charts may be located on stickers on the HVAC unit itself, or they may be part of the schematic. Information may even be printed right on the control board, near the selections. The charts and complete instructions about each setting and how it affects the operation of the HVAC system are always found in the installation and/or service manual. Most HVAC system manufacturers create one manual for each model line they produce, and that manual contains all of the charts for every unit in that model line. There- fore, it is important to find the chart or charts that match the precise model number for the system on which you are working.

Most fossil fuel heating systems have the heating airflow preset at the factory to operate with a temperature rise that is within a few degrees of the midpoint of the temperature rise range specified on the unit rating (data) plate. However, the technician should always measure the temperature rise and compare it to the information on the unit rating plate. There are several ways to modify the heating airflow if the temperature rise does not meet the specified range, or if adjustments are needed to improve airflow or register temperature.

The chart shown in Figure 5 (this time from Trane^{® 3}) provides detailed temperature rise, airflow, and power values related to a pair of switch settings. Note that the factory default setting is identified as “Normal.” Also, notice that even though the values for first-stage and second-stage heat are given, there is only one selection that modifies the airflow for both stages.

Figure 4: Airflow data (York^® TM9V)

For most systems, the cooling air ow is also the heat pump heating air ow. Most units designed to be used in split systems are capable of operating with multiple sizes (capacities) of A/C or heat pump systems. Therefore, the factory default selection always must be checked and adjusted to match the installation.

Figure 6 shows an example of a chart from Trane that allows for the selection of cooling air ow by unit capacity (tonnage) and the ability to set the air ow at 350, 400, or 450 cfm per ton for more or less latent heat removal (dehumidification). In this example, four switches must be adjusted to achieve the proper selection.

These are just few examples of how different manufactures provide charts and functions for selecting air ow. Constant air ow driven systems also have many other options for selecting comfort features such as improved dehumidification and continuous fan. While many are similar, it’s important to be familiar with and follow the instructions provide for each individual HVAC system.

Many HVAC manufacturers also now offer communicating thermostats with on-screen menus. These menus may include some or all of the air ow and comfort selections previously discussed, as well as advanced diagnostic features and real-time operational values, such as cfm and TESP (total external static pressure). If the HVAC system control board utilizes DIP switches or jumper pins, their settings may be superseded by the communicating thermostat menu selections. Again, be sure to check the HVAC manufacturer’s literature for information related to these advanced thermostats.

Figure 5: Heating airflow (cfm) and power (watts) vs. external static pressure with filter for gas furnace (Trane UY080RV3W)

Figure 6: Cooling airflow (cfm) and power (watts) vs. external pressure with filter for gas furnace (Trane UY080RV3W)

Constant torque ECMs

Constant-torque ECMs are most commonly built using a multi-tap design similar to that of a PSC induction motor. Each tap (usually called a “speed tap”) is actually programmed with a torque value. The torque value for each tap is stored in the motor control. When the tap is energized, the motor control operates the motor at that value. This is also very similar to an induction motor in which the motor winding is tapped to create multiple speeds based on the torque created by each tap. However, that is where the similarities end. The Genteq^® model Endura^® Pro motor is an example of a multi-tap constant-torque ECM (see Figure 7).

The motor control is powered with continuous line voltage when the HVAC system’s disconnect is closed. The high-voltage terminals on the connection block of all Endura® Pro motor controls, regardless of the rated voltage, are labeled “L” (Line 1), “G” (ground), and “N” (neutral). The “N” terminal is connected to the neutral line on 15-V ac and 277-V ac systems, or to Line 2 on 208-/230-V ac and 460-V ac systems. Each model is built to operate at a single voltage source.

Figure 9: Example of airflow table (partial) for single-stage gas furnace

*“GE” is believed to be a trademark or trade name of the General Electric Co. ¹ Regal Rexnord, Genteq^® are trademarks or trade names of Regal Rexnord Corp. or one of its affiliated companies.

² York is believed to be owned by Johnson Controls International plc or one of its affiliated companies. ³ Trane is a subsidiary of Trane Technologies.

Christopher Mohalley is the Training Manager for Regal Rexnord. He has applied his 25+ years of HVAC field experience, instruction and extensive product training to create a nationally-recognized ECM training program. He serves as a NATE Technical Committee SME, is a member of RSES and is NATE certified in all HVAC disciplines.

Interested in reading more about this topic? Check out Mohalley’s book Understanding Electronically Commutated Motors (SKU 200-523x), published as a part of the RSES Sustainability Series at www.rses.org/store. Use promo code ECM2020 and get 10% off the purchase price.

"EC Indoor Blower Motors, Resistance is Futile", by Christopher Mohalley. June 2020 feature reposted with permission from RSES Journal, www.rsesjournal.com.