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3.3.7
Supply air Temperature Rise Test
1.
Operate the burner for at least 10 minutes;
2.
Measure the air temperature in the return air plenum;
3.
Measuring the air temperature in the largest trunk coming off the
supply air plenum, just outside the range of radiant heat from the
heat exchanger. 0.3 m (12") from the plenum of the main take-off
is usually sufficient;
4.
The temperature rise is calculated by subtracting the return air
temperature from the supply air temperature;
5.
If the temperature rise is lower or exceeds the temperature
specified in Table 7, p.13, change to the next lower or higher
blower speed tap, until the temperature rise falls to the target. If
the excessive temperature rise cannot be increased or reduced
by changing fan speed, investigate for ductwork obstructions,
dirty or improper air filter, improper firing caused by improper
pump pressure or nozzle sizing.
3.3.8
Limit Control Check
After operating the furnace for at least 15 minutes, restrict the return
air supply by blocking the filters or the return air register and allow the
furnace to shut off on High Limit. The burner will shut off but the
blower will continue to run.
Remove the obstruction and the burner should restart after a few
minutes. The time required for the restart also depends on the
adjustment of the blower "OFF" delay.
3.3.9
Restart after burner failure
1.
Set the thermostat lower than room temperature;
2.
Press the reset button on the burner primary control (relay)
3.
Set the thermostat higher than room temperature;
4.
If the burner motor does not start or ignition fails, turn off the
disconnect switch and CALL A QUALIFIED SERVICE
TECHNICIAN.
CAUTION
Do not attempt to start the burner when excess oil has
accumulated, when the furnace is full of vapour or when
the combustion chamber is hot.
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