Checking Capacitor; Testing Capacitor Resistance; S-9A Ecm Motor Interface Board; S-10A Resistance Check - Amana GUIA070A30 Service Instructions Manual

S-9A ECM MOTOR INTERFACE BOARD

GUIV model furnaces use an ECM blower motor. These mo-
tors use an electronic control module attached to the mo-
tors end bell to control motor operation. Some unique fea-
tures of the ECM motor are:
1. Constant Airflow. These motors will maintain constant
airflow in excess of .80 static. In other words, as the
static increases so does the motors RPM so that a con-
stant CFM is maintained.
Note: The motor in these units will move more air under
higher static conditions than a similar sized unit using a
PSC motor. Because this motor does not load up and re-
duce airflow like a PSC motor, in some undersized duct
installations this may cause noise or high airflow complaints.
2. Ramp-up/Ramp-down feature. These motors ramp up
and down at the beginning or end of a cycle to reduce air
rush noise.
3. High voltage is present at these motors all the time. Motor
operation is controlled through the low voltage motor in-
terface board.
A motor interface board, mounted on the control bracket is
used to control blower operation in 3 modes of operation.
Fan only, cooling speed, and heating speed. Refer to the
airflow table in the BLOWER PERFORMANCE section of
this manual for details.
The cooling and heating speeds are adjusted by relocating
the jumper pins on the motor interface board. Refer to Speed
Tap Adjustments figure on page 44.
There is a LED on the motor interface board that serves to
indicate the airflow that the motor is supposed to be deliver-
ing, depending upon the positioning of the pin selectors on
the interface board. The number of blinks multiplied by 100
yields the programmed CFM (Example: 10 Blinks x 100 =
1000 CFM). The indicated CFM may vary, depending on the
mode of operation and the signals being sent to the control
board at the time.
Note: An inductor (Power Correction Factor Choke) is re-
quired when powering 3/4 horsepower ECM motors with 115
volts. The operation of this inductor is to reduce the line
current by storing the electrical energy in a magnetic field,
such that the voltage AC waveform leads the current AC
waveform. In other words, the inductor reduces line current
which extends the life of the 3/4 horsepower ECM motor.
The furnaces requiring this inductor are the GUIV090,115,
140DX50 models.
IMPORTANT: If the inductor fails, there will be no motor
operation since this is the LINE power supply, black wire
(BK-6), from the integrated ignition control to the motor. To
determine if the inductor is at fault, you can bypass by the
inductor by disconnecting the black wire (BK-6) wire from
the inductor and connecting it directly to the motor. If the
motor operates then the inductor will need to be replaced.
80
Rev. 2
SERVICING
S-10 CHECKING CAPACITOR
The direct drive motors are of the permanent split capacitor
design. A run capacitor is wired across the auxiliary and a
portion of the main windings. The capacitors primary func-
tion is to reduce the line current while greatly improving the
torque characteristics of a motor. This is accomplished by
using the 90° phase relationship between the capacitor cur-
rent and voltage in conjunction with the motor windings so
that the motor will give two phase operation when connected
to a single phase circuit. The capacitor also reduces the
line current to the motor by improving the power factor to the
load.
WARNING
DISCHARGE CAPACITOR THROUGH A 20 TO 30 OHM
RESISTOR BEFORE HANDLING
Two quick ways to test a capacitor are a resistance and a
capacitance check. Refer to the next two figures for proper
meter connections for the resistance and capacitance test-
ing of the capacitor.

S-10A Resistance Check

WARNING
Disconnect Electrical Power Supply:
1. Remove blower compartment door to gain access to ca-
pacitor.
2. Discharge capacitor and remove wire leads.
3. Set an ohmmeter on its highest ohm scale and connect
the leads to the capacitor.
a. Good Condition - indicator swings to zero and
slowly returns toward infinity.
b. Shorted - indicator swings to zero and stops there
- replace.
Volt / Ohm
Meter

Testing Capacitor Resistance