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SERVICING
WARNING
Discharge capacitor through a 20 to 30 OHM resistor before
handling.
2. Connect the Meter leads to the Capacitor terminals.
3. Digital meter will show a reading momentarily (Figure 1).
Note the reading.
Figure 1
Figure 2
4. Reading will immediately return to the OL = (Open Line)
(Figure 2). Every attempt of Step 2 will show the same
result as was in step 4 and Step 5. This indicates that the
capacitor is good.
5. If there is no Change, then capacitor is dead and must be
replaced.
Check for Analog Meter
A. Good Condition - Indicator swings to zero and
slowly returns to infinity. (Start capacitor with bleed
resistor will not return to infinity. It will still read the
resistance of the resistor.)
B. Shorted - Indicator swings to zero and stops there -
Replace.
C. Open - No reading - Replace. (Start capacitor would
read resistor resistance.)
S-15B CAPACITANCE CHECK USING A DIGITAL
MULTI-METER (IN CAPACITANCE MODE)
WARNING
Discharge capacitor through a 20 to 30 OHM resistor before
handling.
NOTE:
You can do this test with a multi-meter if you have a
Capacitance meter on your multi-meter.
1. Remove the capacitor from the circuit.
2. Now Select “Capacitance” on your multi-meter.
3. Now connect the capacitor terminals to the multi-meter
leads.
4. If the reading is near to the actual value of the capacitor
(i.e. the printed value on the capacitor). The capacitor is
good. (Note that the reading may be less than the actual
printed value of the capacitor.)
5. If you read a significantly lower capacitance or none at all,
then capacitor is dead and must be replaced.
S-16G CHECKING EMERSON ULTRATECH™
ECM MOTORS
DESCRIPTION
The DVPTC and MBVC models utilize an Emerson, 4-wire variable
speed ECM blower motor. The ECM blower motor provides
constant CFM.
The motor is a serially communicating variable speed motor.
Only four wires are required to control the motor: +Vdc,
Common, Receive, and Transmit.
The +Vdc and Common wires provide power to the motor’s low
voltage control circuits.
GENERAL CHECKS/CONSIDERATIONS
1. Check power supply to the air handler or modular blower.
Ensure power supply is within the range specified on
rating plate. See section S-1.
2. Check motor power harness. Ensure wires are continuous
and make good contact when seated in the connectors.
Repair or replace as needed.
3. Check motor control harness. Ensure wires are continuous
and make good contact when seated in the connectors.
Repair or replace as needed.
4. Check thermostat and thermostat wiring. Ensure
thermostat is providing proper cooling/heating/
continuous fan demands. Repair or replace as needed.
5. Check blower wheel. Confirm wheel is properly seated on
motor shaft. Set screw must be on shaft flat and torqued
to 165 in-lbs minimum. Confirm wheel has no broken or
loose blades. Repair or replace as needed.
6. Ensure motor and wheel turn freely. Check for
interference between wheel and housing or wheel and
motor. Repair or replace as needed.
7. Check housing for cracks and/or corrosion. Repair or
replace as needed.
8. Check motor mounting bracket. Ensure mounting bracket
is tightly secured to the housing. Ensure bracket is not
cracked or broken.
