MODEL F80A
AIRFLOW
For proper furnace operation, airflow over the heat exchanger is of utmost importance. Insufficient airflow accelerates metal fatigue and failure in the heat exchanger and excessive airflow promotes accelerated corrosion of the heat exchanger. IMPORTANT: Do not bypass this step of the start up procedures.
CALCULATING AIRFLOW
There are circumstances where it may be desirable to know the airflow delivery through the duct system, such as when
SETTING BLOWER "OFF" TIMINGS
Both control systems allow flexibility in the FAN OFF delay function. The control is located in the blower compartment. Follow the same steps as listed in Adjusting Blower Speeds to access the control.
DIP SWITCH
HEAT "OFF" DELAY
SW 1 | SEC. | |
|
|
|
ON | ON | 60 |
|
|
|
OFF | ON | 90 |
|
|
|
ON | OFF | 120* |
|
|
|
OFF | OFF | 180 |
|
|
|
estimating the amount of airflow available for air condition- ing. This can be done by direct measurement with electronic or sloped manometers and velometers, or by using the for- mula below.
Where:
Cfm is airflow in cubic feet per minute ΔT is the temperature rise
Bonnet output is the furnace output capacity from the rating plate.
NOTE: The bonnet output will vary directly with the input. If the actual input is below the stated input, the output will be reduced in the same ratio.
ADJUSTING BLOWER SPEEDS
If the blower speeds require adjusting, follow these steps:
WARNING
DISCONNECT THE ELECTRICAL SUPPLY TO THE FURNACE BEFORE ATTEMPTING TO CHANGE THE BLOWER SPEED. FAILURE TO DO SO COULD RESULT IN ELECTRICAL SHOCK RESULTING IN PERSONAL INJURY OR LOSS OF LIFE.
1.Remove the blower compartment door.
2.Access the motor electrical wiring.
The blower speed is changed at the integrated furnace control. Remove the wire from the "HEAT" terminal of the
IMPORTANT: If the heating speed and cooling speed are to be the same, remove the cooling lead from the control, tape it off, then install a “piggyback” connector from the control “HEAT” terminal to the “COOL” terminal. UNDER NO CIRCUMSTANCE MAY TWO MOTOR WINDINGS BE POWERED SIMULTANEOUSLY.
3.Slide the blower assembly back into position, and refasten with the sheet metal screws.
4.Reinstall the blower compartment door.
5.Recheck temperature rise.
NOTE: Temperature rise should always be rechecked whenever blower speed changes are done.
Figure 11: 50A55-250 Dip Switch Settings
These dip switches control the “Blower off” timing
HOW TO REMOVE THE BLOWER
1.Disconnect power from furnace.
2.Remove thermostat wiring from the integrated furnace control.
3.Remove L1, Neutral and Ground connections between the integrated furnace control and the Furnace electrical connection junction box.
4.Remove 12 pin male molex connector from female connection point, and ground connection from integrated furnace control.
5.Unscrew 2 blower housing bolts located in the front blower shroud as indicated in figure 12 below. Remove front blower shroud from furnace.
6.Slide blower assembly towards front of furnace. Blower is mounted on rail system, and will slide forward about 10 inches before blower is clear of rails.
HOW TO INSTALL THE BLOWER
1.Place blower into blower compartment.
2.Keep blower assembly tight to top of blower compartment. Line up blower assembly to slide into blower rails. Push blower assembly towards back of furnace ensuring blower assembly is correctly placed in blower rails. Insert blower shroud on the front of the blower housing. Insert blower housing bolts and tighten.
3.Connect thermostat wiring to the integrated furnace control.
4.Connect L1, Neutral and Ground connections between the integrated furnace control and the furnace electrical connection junction box.
5.Connect 12 pin male molex connector to female connection point, and ground connection to the integrated furnace control.
6.Turn on power to the furnace.
Figure 12: Blower bolts
Bolts
19
