MGD Gas Furnace
Service Manual
Blower Assembly removal and replacement
1. Disconnect electrical power to the furnace.
2. Remove the blower access panel.
3. Unplug blower-wiring harness from plug in top of control box.
4.
Remove the four screws securing the blower housing
.
5. Slide entire housing to the left to disengage the tabs holding the right side.
6. Pull back on top of blower and lift bottom to disengage the two tabs on the bottom side.
7. Lift blower assembly out of furnace cabinet.
8. Installation is the reverse of these removal steps.
Blower wheel inspection
Visually inspect the blower wheel for accumulations of dirt or lint which will reduce airflow. Clean
the blower wheel of any accumulations.
BLOWER SPEEDS
The wide variety of applications and installations of furnaces throughout the country makes it
impossible to factory select blower speeds that will provide proper operation for all installations.
The blower speeds for both heating and cooling must be field selected for each particular
installation to insure proper operation.
The criteria for selecting the proper blower speeds
IS
NOT
High
for cooling, Low for heating. That
may be how it works out SOMETIMES but it can be exactly the opposite.
The PROPER CRITERIA FOR SELECTING BLOWER SPEEDS is as follows:
A blower speed must be selected that will provide proper temperature rise through the furnace.
See Checking Temperature Rise found elsewhere in this manual. The required CFM for a
particular temperature rise can also be calculated by using the following formula:
Output BTU
Temp. Rise X 1.08 = CFM
EXAMPLE: A model MGD75-E3A has an output of 60,000 Btuh. A temperature rise of 60°F
(range of 45-75°F allowable) is desired. Measured external static pressure is 0.3” W.C. with a
dry
coil.
60,000 or 60,000 = 926 CFM
60 X 1.08 64.8
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