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.
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 .
Modern thermostats do not have this type of heat
anticipator. Many have a selector switch to adjust the
number of cycles per hour.
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
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
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.
D
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.
ECM control connections are made through the integrated
ignition control. No other control connections are needed.
(Factor Power Choke Correction)
To Next Page
Loading...
