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
