46
Figure 16.
:
The CMA/CMC furnace models are direct vent design and do
not require an air shutter adjustment (air shutters are not used) for proper
flame characteristics. Burner box access cover must always be secured
with all screws in place and tightened before operating furnace.
E. SETTING TEMPERATURE RISE
All CMA/CMC Models are designed and wired at the factory for a heating blower
speed that should result in an approximate temperature rise of 55
°
F for CM**50’s
and 65
°
F for CM**75’s. The blower motors are wired on med-low speed for
heating mode. The temperature rise through the furnace may vary depending on
the duct system, elevation, heating value, etc. for each installation. A lower
temperature rise will result in a higher efficiency. Temperature rise = supply air
temperature - return air temperature.
After 10 to 15 minutes of continuous operation, the temperature rise through the
furnace must fall within a range of 40
°
F to 70
°
F for CM**50’s and 50
°
F to 80
°
F
for CM**75’s. If the outlet or supply duct temperature is too high, you should
check to make sure that your return air filter is clean, your return air openings are
free from obstruction, your outlet registers are properly adjusted and clear and
your supply and return air ducts are open.
The circulating air blower is not moving enough air if the supply air temperature is
still too high. Before proceeding further, turn off the power supply to the furnace
and remove the front door of the unit.
The speed of the blower must be increased by changing the speed tap from the
motor (see figure 15). This is accomplished by locating the control panel attached
to the blower housing and switching blower lead connected to the “Heat” terminal
on the White-Rodgers 50A65-143 control, with one of the higher speed blower
leads attached to a terminal marked “Park”. Be sure to attach any unused blower
leads to a terminal marked “Park”. Replace the blower door and turn on the
power supply.
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