SERVICING
29
9. If the furnace blower motor starts and the condensing
unit runs, then the trouble is in the thermostat or wiring.
Repair or replace as necessary.
10. After completing check and/or repair of wiring and
check and/or replacement of thermostat, reinstall blower
compartment door.
11. Turn on electrical power and verify proper unit operation.
HEATING ANTICIPATOR
On older thermostats, the heating anticipator is a wire
wound adjustable heater which is energized during the
“ON” cycle to help prevent overheating of the conditioned
space.
The anticipator is a part of the thermostat and if it should
fail for any reason, the thermostat must be replaced.
The heating anticipator setting for furnaces covered in this
manual is
0.70 Amps
.
Modern thermostats do not have this type of heat
anticipator. Many have a selector switch to adjust the
number of cycles per hour.
CHECKING TRANSFORMER AND CONTROL
CIRCUIT
A step-down transformer 120 volt primary to 24 volt
secondary, 40 VA (Heating and Cooling Models) supplies
ample capacity of power for either operation.
WARNING
High Voltage!
Disconnect all power before servicing
or installing this unit. Multiple power
sources may be present. Failure to do
so may cause property damage, personal
injury or death.
1. Remove blower compartment door to gain access to
the thermostat low voltage wires located at the furnace
integrated control module.
2. Remove the thermostat low voltage wires at the furnace
integrated control module terminals.
With Power On (and Door Interlock Switch closed):
WARNING
Line voltage now present
3. Use a voltmeter, check voltage across terminals R and
C. Must read 24 VAC.
4. No voltage indicates faulty transformer, open fuse, bad
wiring, bad splice, or open door interlock switch.
5. Check transformer primary voltage at incoming line
voltage connections, fuse, splices, and blower door
interlock switch.
6. If line voltage is available to the primary side of
transformer and not at secondary side, the transformer
is inoperative. Replace.
7. After completing check and/or replacement of transformer
and check and/or repair of control circuit, reinstall blower
compartment door.
8. Turn on electrical power and verify proper unit operation.
4-Wire ECM Motors
D
escription
These models utilize an Nidec US motors, 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. Typical supply voltage is 9-15
volts DC.
CHECKING AIR CIRCULATION BLOWER
MOTOR (ECM MOTORS)
ECM Control Connections
ECM control connections are made through the integrated
ignition control. No other control connections are needed.
NOTE: An inductor
(Factor Power Choke Correction)
is required when powering the 3/4 and 1
horsepower motors with 115 volts (inductor
pictured below). 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
and 1 horsepower motors.
IMPORTANT: If the inductor fails, there will
be no motor operation since this is the “LINE”
power supply, black wire, 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 from
the inductor and connecting it directly to the
motor. If the motor operates then the inductor
will need to be replaced.
