ECM Motors

TECH TALK

I often get calls from technicians wondering what the “best” way is to test an ECM motor.  That’s a difficult question to answer in less than 30 seconds.  The Carrier/Bryant factory publishes a very comprehensive diagnostic troubleshooting guide, but rarely have I seen anyone actually use it.  That being said, I decided it would be best to publish a short article on quick ECM motor diagnostic techniques.

Before getting into the actual checks, let’s make sure we understand the basics of how ECM motors work.  The ECM blower motor is first fed 120 VAC power through the 5-pin connector.  The 120 VAC power is then rectified to DC by a diode module.  After rectification, the DC signal is electronically commutated and fed in sequential order to 3 stator windings. The frequency of commutation

pulses determines motor speed.  In a nutshell, the P.C. Board is communicating with the module to determine Torque, RPM and Pulse Frequency. 

Knowing this helps to understand that even with voltage present, the circuit board communications need to be active and functioning for the motor to work.  The motor module must also be functioning to properly control the motor.  If either is defective, the motor will not turn.

First.   Initiate a call for fan on the circuit board or from the thermostat and check with your meter for 120 VAC at the motor.  2.  If there is 120 VAC present then turn power off to the furnace or fan coil and remove the blower.  Then remove the motor module and visually inspect for damage or burnt components inside.  3.   Turn the motor and see if it turns freely.  Note that the motor has an internal brake and will stop the wheel before too many revolutions.  4.  Set your OHM meter to the highest setting and OHM each of the 3 motor leads to the un-painted motor end shield.  You should read > 100k OHMs on each lead.  If so, the motor passes this test.  5.  OHM out each of the 3 leads to each other (1 to 2, 1 to 3 & 2 to 3).  Each should read less than 20 OHMS and should be nearly equal or within + 10%.  6.  If the motor turns freely and passes the listed OHM’s tests, the motor is fine.  You either have a bad module or bad circuit board. 

Most of the time the motor is fine, but the module or circuit board has failed.  At this point, if you don’t have a definitive answer on which component is bad, you should refer to the manufacturer’s detailed troubleshooting guide or purchase a TECMate Pro tester.  This will simulate the circuit board’s call for fan by allowing you to manually turn the fan on/off.  If you are able to energize the fan with the TECMate Pro, then you have a bad circuit board or wiring harness.  The part number for the TECMate Pro is: GE-A447 and is available at our store.  The good news is that this TECMate Pro will work on all or most all Genteq ECM motors used in our industry.  The exception is the X-13 motor.  It is not designed to work on the X-13.  

The specific ECM troubleshooting guide for the Carrier/Bryant product you’re working on can be downloaded from www.HVACPartners.com.   You may also want to refer to www.dealertoolbox.com or download the Genteq App from the App store for additional troubleshooting references.

Although this is not a 100% comprehensive troubleshooting guide on ECM motors, many times this “short list” of troubleshooting tips will lead you to the problem and save you a significant amount of time

Good Luck

Magnum

Engineering

Engineering is the application of physics, science, experience, economics, and practical knowledge in order to design, improve, maintain a system, structure, or a process. In the HVAC world, there are various levels of engineering needed and performed. This ranges from the practical knowledge of a trained contractor to the expertise of a larger engineering firm. The goal should be always the same. To create a high performance system with reliable, serviceable, and predictable results.

At Contractors HVAC Supply, we have organized a team with a range of experience in commercial and residential from an Engineer with experience from a consulting engineering firm and Carrier University training. We also have people experience with field installs, service, factory training, sales expertise, etc. We strive to work closely with our contractors and the local engineering community to provide solutions with our quality equipment, product knowledge, and proper application of our equipment.

WP_CAR_VRF

WP_CAR_VRF

Variable refrigerant flow (VRF) systems vary the flow of refrigerant to indoor units based on demand.

This ability to control the amount of refrigerant that is provided to fan coil units located throughout a 

building makes the VRF technology ideal for applications with varying loads or where zoning is 

required.  

WP_CAR_CommercialFanApplication

WP_CAR_CommercialFanApplication

The indoor fan is a critical component in every forced-air, space-conditioning system. The fan is

the principal means for delivering conditioned air to a space, and therefore the effectiveness of the fan

has a direct impact on system efficiency, perceived comfort level, and air quality in the space. There are

a variety of fan types and arrangements, each with unique operating properties that lend themselves to

particular applications and design requirements.

WP_CAR_IndoorCoilCorrosion

WP_CAR_IndoorCoilCorrosion

Indoor coil corrosion leading to coil failure is an issue that affects coils manufactured by the entire

HVAC industry today. A leading cause of coil corrosion is formicary acid, an organic acid that

can be formed in the home. Although the occurrence rate of these failures is low nationwide,

some geographic areas have experienced higher incidence rates. For instance, some homes

experience multiple corrosion-related failures while those around them have none. Failures are

typically characterized by leaks that form in the fin pack area of the coil after one to four years of

installation and use.

WP_CAR_FurnaceHeatExchangerSooting

WP_CAR_FurnaceHeatExchangerSooting

Heat exchanger sooting in 90% multi-poise condensing furnaces can begin to form from

several sources. The two most common are improper setup and maintenance, and high

sulfur levels in the fuel. The intent of the following information is to address the operational

changes of the furnace based on high sulfur levels as well as furnace setup and mainte-

nance. The sources of high sulfur will also be addressed.

Keeping Connected

With the rapid pace of technology improvements and equipment changes, it’s important we keep up with the demands of our industry.   We have many electronic resources available to you that will make you a more efficient and informed technician. 

               One of the most important resources from a Carrier/Bryant standpoint is access to HVAC Partners Web Site.  On this site you will have access to all current and past literature for Installation, Service, Wiring, Troubleshooting, Engineering Data, etc.  You just need to log onto www.HVACPartners.com and submit a request for access.  This will normally take 1-2 business days, and you will be notified of a username and password for future access.  

               Additionally, there are lots of FREE Apps for your Smartphone.  Log onto EmersonClimate.com/mobileapp to download a Temperature & Pressure Chart App, Compressor Troubleshooting App (for air conditioning & refrigeration systems) or Check & Charging App just to name a few. 

               You may also just browse the App Stores for your iPhone or Android to find many other useful Apps that will help you every day in the field.

               As always, if you can’t find what you need, I am here to assist you with your Technical questions or problems.  I look forward to speaking with you!

Magnum