21
SERVICING
3. Subtract the return air temperature from the supply
air temperature to determine the air temperature rise.
Allow adequate time for thermometer readings to
stabilize.
4. Adjust temperature rise by adjusting the circulator
blower speed. Increase blower speed to reduce
temperature rise. Decrease blower speed to increase
temperature rise. Refer to Circulator Blower Speed
section in the Product Design section of this manual
for speed changing details. Temperature rise is relat-
ed to the BTUH output of the furnace and the amount
of air (CFM) circulated over the heat exchanger.
Measure motor current draw to determine that the
motor is not overloaded during adjustments.
All use a nonadjustable, automatic reset, bi-metal type limit
control. Refer to the following drawing for the location of the
primary limit.
Style 1 drawing illustrates the Primary Limit used on the 80%
furnaces.
-
-
1. Remove burner compartment door to gain access to
the primary limit.
2. Remove low voltage wires at limit control terminals.
3. With an ohmmeter, test between these two terminals
as shown in the following drawing. The ohmmeter
should read continuous unless heat exchanger tem-
perature is above limit control setting. If not as above,
replace the control.
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