diagnosing - Meier Supply

diagnosing - Meier Supply
Service Clinic
GE ECM motors,
like the 2.3 pictured
here, are easy to
service because
the electronic
components are
separate from the
motor module.
he ability to move air rapidly and efficiently in HVAC systems is essential to
achieving a cost-efficient comfort system.
The electrical motors that were used in
HVAC applications were AC induction
style motors that were either single- or
multi-speed — they’d run at one speed
for heating, another for cooling, and sometimes a
third speed for two-stage systems.
The problem with these types of motors is that
they use a lot of energy because they run at full
amp draw at all times — even during off-demand
cycles. Also, since the motors run on high speed
all the time, the noise levels are also high.
To address these two concerns — efficiency
and noise — the electronically commutated motor
(ECM) was developed. According to GE, an innovator in ECM technology, the wide range of the
ECM motor, high efficiency, and programmability
gives it a virtually unlimited range of performance
Of course, the increasing popularity of the ECM
motor has led to a number of questions from technicians on how to service and troubleshoot ECMdriven systems.
GE offers a few basic checks that technicians
should perform before troubleshooting the
ECM motor. One thing to always keep in mind,
however, is to always consult the manufacturer’s guide to confirm proper configurations
and demands.
Verify that the correct thermostat input
voltage is present at the interface of the
main control board on the furnace or air handler.
Loose or broken low-voltage wires can potentially
cause intermittent problems.
When checking low-voltage connections,
always use the C terminal on the board,
never on the ground.
The GE-ECM Service Guide’s illustrations help
technicians visualize troubleshooting.
Check the setting of the jumper
pins or DIP switches on the
manufacturer’s control board. Don’t assume they are correct; use the manufacturer’s guide to select the proper airflow, delays, and profiles. And, be sure
to always disconnect the main power to
the unit when making these adjustments.
Check all terminal/plug connections both at the HVAC system
control board, and at the motor. Look
for loose plugs and/or loose pin connections in the plug, and for burnt, bent or
loose pins or seats.
Confirm there are no limits, rollouts, or safeties tripped. Also
check for any fault codes present on the
control boards. If fault codes are present, consult the manufacturer’s recommendations to resolve the problem.
If these checks don’t resolve the
problem, or if the fault code reveals a
motor problem, then it’s time for some
additional diagnostics.
For most models of ECM motors, it is
normal for the motor to rock back and
forth on start up. If this is the only symptom identified, there is no need to replace the motor.
However, if the system is excessively
noisy, doesn’t appear to change speeds
in response to a demand for heat or cooling, or is having symptoms during the
cycle such as a tripping limit or freezing
coil, there are a number of checks that
can be performed.
Wait for programmed delays to time
out. If delays are too long, then reset
them using the manufacturer’s chart.
Ensure the airflow settings are correct
for the installed system using the charts.
Remember that the change in airflow
between continuous-fan speed and low
stages of operation may be very slight
depending on the size of the system. If
the system is operating normally in each
stage, then there is no problem.
ECM Service Tech Tips
Tech Tip 1: Don’t automatically assume the ECM motor has failed. Make
sure you go through the diagnostic steps completely before replacing
the motor.
Tech Tip 2: When it’s necessary to disconnect the power from the HVAC
system, it’s always a good practice to verify that voltage has been
disconnected, by using a voltmeter.
Tech Tip 3: A True-RMS meter isn’t needed to check high- or low-voltage
to the motor.
Tech Tip 4: If you must replace the 2.0, 2.3, or 2.5 control module, then
be sure to use a direct replacement from the manufacturer. ECM control
modules are factory programmed for specific manufacturer applications.
If you use the wrong control module, it will void all product warranties
and may result in improper or no blower operation.
Tech Tip 5: If a check of the control module indicates replacement is
required, then also check the motor module. Installing a new control on
a failed motor will result in the new control also failing.
Tech Tip 6: Always pull the connector and not the wires. Most
connectors are also keyed. Reconnecting a connector the wrong way
could damage the motor.
Tech Tip 7: When checking any plug connector, the meter leads are most
likely larger than the terminals or socket. Using thin leads will prevent
the terminals from being damaged by a voltage check.
— From the GE ECM Service Guide
circle 60 on reader service card
Service Clinic
Remove the filter and check that all of
the dampers, registers, and grills are
open and free-flowing. If removing the
filter corrects the problem, clean or replace with a less restrictive filter.
Also, check and clean the blower
wheel, secondary heat exchanger, and
evaporator coil. If this doesn’t correct
the problem, then check the external
static pressure. If it’s higher than the
manufacturer’s recommendations, then
correct the airflow restriction.
If the motor does not shut off at the
end of the cycle, check the delay times
and wait for delays to time out. Make
sure that there is no call for “continuous
fan” on the G terminal. This motor may
take a while to come to a complete stop
with selected delays and the normal
ramp down.
There are also a few checks you can
perform if the ECM motor is not running. First, check for proper high-voltage
and ground at the five-pin connector at
the motor. Correct any voltage issues before proceeding.
ECM motors are dual voltage motors
capable of operating in 120 or 240VAC
systems. On the 120VAC systems, there
should be a jumper between terminals
one and two. On 240VAC systems, the
jumper should be removed. If the motor
is operating at 240VAC with the jumper
in place, the motor will be permanently
GE ECM certified master trainer
Christopher Mohalley’s service
training classes help distributors,
contractors, technicians, and
instructors understand all aspects of
ECM technology, from the
sophisticated electronic components
to simple set-up, diagnostics, and
repair of variable-speed blower
motors. Offering one hour, 2-4 hour,
or full day sessions, classes are made
for professionals across a wide range
of technical backgrounds — from
apprentice to certified master
For more information on this topic, go
to: www.thedealertoolbox.com.
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