Table of Contents
Advertisement
This tells us that in one hour, the furnace would consume
78 cu. ft. of gas (3600 / 46 = 78).
The typical value range for 1 cu. ft. of natural gas is around
1025 BTU. Check with your gas utility, if possible. In this
example, the furnace is consuming 80,000 BTUH.
NOTE: The final manifold pressure cannot vary
by more than ± 0.2" w.c. for Natural gas from the
specified setting. Consult your local gas supplier
if additional input rate adjustment is required.
4. Turn ON gas to and relight all other appliances
turned off in step 1. Be certain that all appliances
are functioning properly and that all pilot burners (if
applicable) are operating.
Temperature Rise
Air temperature rise is the temperature differench between
supply and return air. The proper amount of temperature
rise is usually obtained when the unit is operated at the
rated input with the "as shipped" blower speed. If the
correct amount of temperature rise is not obtained, it may
be necessary to change the blower speed.
Temperature rise must be within the range specified on the
unit rating plate. An incorrect temperature rise may result
in condensing in or overheating of the heat exchanger.
The temperature rise of the furnace must be within the
temperature rise range listed on the furnace rating plate.
Determine and adjust temperature rise as follows:
1. Operate furnace with burners firing for approximately
ten minutes. Ensure all registers are open and all
duct dampers are in their final (fully or partially open)
position.
2. Place thermometers in the return and supply ducts as
close to the furnace as possible. Thermometers must
not be influenced by radiant heat by being able to
"see" the heat exchanger.
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 Startup Procedure and
Adjustment - Circulator Blower Speeds for speed
changing details.
Temperature Rise Measurement
OPERATIONAL CHECKS
SAFETY CIRCUIT DESCRIPTION
To avoid personal injury or death, do not remove internal
compartment covers or attempt any adjustment. Electrical
components are contained in both compartments. Contact
a qualified service agent at once if an abnormal operation
should develop.
Do not bypass safety devices.
A number of safety circuits are employed to ensure safe
and proper furnace operation. These circuits serve to
control any potential safety hazards and serve as inputs
in the monitoring and diagnosis of abnormal function.
These circuits are continuously monitored during furnace
operation by the integrated control module.
Integrated Control Module
The integrated control module is an electronic device
which, if a potential safety concern is detected, will take the
necessary precautions and provide diagnostic information
through an LED.
Primary Limit
The primary limit control is located on the partition panel
and monitors heat exchanger compartment temperatures.
It is a normally closed (electrically), automatic reset,
temperature activated sensor. The limit guards against
overheating as a result of insufficient conditioned air
passing over the heat exchanger.
34
SUPPLY
AIR
RETURN
AIR
Figure 51
CAUTION
WARNING
Advertisement
Table of Contents
