Variable Speed Motor
Units equipped with a variable speed circulation air blower motor will deliver a constant airflow within a wide range of external static pressures. Other features of this variable speed motor include:
Soft Start/Stop – The variable speed motor will slowly ramp up to normal operating speed. This minimizes noise and increases comfort by eliminating the initial blasts of air encountered with standard motors. At the end of a cooling or heating cycle, the motor will slowly ramp down.
Circulation Airflow Adjustments – The controls include a variable speed motor interface board. The ADJUST tap can be used to raise (+) or lower
Heating and Cooling Airflows – The units are factory set for the correct heating and cooling airflows. However, airflow changes can be made by moving the position of the HEAT and COOL taps (see Table 4).
Continuous Blower – The comfort level of the living space can be enhanced when using this feature by allowing continuous circulation of air between calls for cooling or heating. The continuous circulation of air occurs at half the full cooling airflow rate. To use this feature, place the thermostat fan switch into the ON position.
Cooling Airflow Ramp Up – At the beginning of a call for cooling, the blower will run at 80% of full airflow for 7.5 minutes. This improves the system’s moisture removal and saves blower power during cooling start.
Reduced Airflow Operation (Dehumidification) – For situations where humidity control is an issue, the variable speed motor can be connected to operate at a 25% reduction in the normal airflow rate. The variable speed motor interface board provides for connection of a humidistat on the HUM terminal. When a humidistat is connected, the dehumidifier resistor on the interface must be cut. The humidistat should be wired to open during high humidity, which will reduce blower airflow.
Safety Controls
The control circuit includes the following safety controls:
Limit Control
This control is located inside the heating compartment and is designed to open at abnormally high air temperatures. It resets automatically. The limit control operates when a high temperature condition, caused by inadequate airflow, occurs. This causes the ignition control to close the gas valve. The circulation air blower continues to operate in this situation.
Pressure Switch
The pressure switch prevents the gas valve and igniter from being energized if there is insufficient combustion air due to a failed combustion blower or a blocked vent.
MAINTENANCE
WARNING
ELECTRICAL SHOCK, FIRE,
OR EXPLOSION HAZARD
Failure to follow the safety warnings exactly could result in dangerous operation, serious injury, death, or property damage.
Improper servicing could result in dangerous operation, serious injury, death, or property damage.
•Before servicing, disconnect all electrical power to furnace.
•When servicing controls, label all wires prior to disconnecting. Reconnect wires correctly.
•Verify proper operation after servicing.
Flame Sensor
If the ignition control does not receive a signal from the flame sensor indicating that the burners have established flame, the gas valve closes after the
Rollout Switch
The switch is located above the main burners. In the event of a sustained flame rollout, the rollout switch causes the ignition control to close the gas valve. To reset, push the button on top of the switch.
Auxiliary Limit (42, 48, and 60 units only)
This control is located in the side of the circulation air blower housing. The switch causes the ignition control to close the gas valve should the circulation blower fail to operate. This control resets automatically.
It is recommended that this furnace be inspected by a qualified service technician at the beginning of each heating season.
Filters
Filters should be checked at least every 6 weeks. Disposable filters should be replaced when dirty, and cleanable filters should be cleaned regularly. It is important to keep the air filters clean, as dirty filters can restrict airflow and the blower and induced draft motors depend upon sufficient air flowing across and through them to keep from overheating.
Lubrication
The blower motor and induced draft motor are
Issue 1008 | Page 13 |
