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SERVICE & TROUBLESHOOTING (CONTINUED)
Table 53.1 - Troubleshooting (Continued)
Trouble
Floating Flames (See Figure 53.1)
Flame Rollout (See Figure 53.2)
Not Enough Heat
Too Much Heat
Power Exhauster Motor Will Not Start
j The duct furnace comes standard with an automatic reset high limit switch that will shut-off the gas should the discharge air temperature become
excessive. See Figure 26.1, indicator (49) for the location of either the standard automatic or optional manual reset high limit switch. The switch
should operate only when something is wrong with the unit operation. Anytime the switch operates, correct the difficulty immediately or serious
damage may result. If the switch cuts off the gas supply during normal operation, refer to the "Not Enough Heat" section of Table 53.1.
Figure 53.1 - Floating Flame Condition
Possible Cause
1.
Insufficient primary air.
2.
Main pressure set too high.
3.
Orifice too large.
4.
Blocked vent cap.
1.
Main pressure set too high.
2.
Orifice too large.
3.
Blocked vent cap.
1.
Unit cycling on high limit. j
a. Obstructions/leaks in duct system.
b. Main pressure set too high.
c. Blower motor not energized.
d. Loose belt
e. Blower speed too low.
f. Blocked/damaged venting system.
g. Defective high limit switch.
2.
Main pressure set too low.
3.
Too much outside air.
4.
Thermostat malfunction.
5.
Gas controls wired incorrectly.
6.
Unit undersized.
1.
Thermostat malfunction.
2.
Gas controls do not shut-off.
a. Gas controls wired incorrectly.
b. Short circuit.
3.
Main gas pressure set too high.
4.
Defective gas valve.
1.
Power supply is off.
2.
No 24V power to thermostat.
3.
Thermostat malfunction.
4.
Defective power exhauster relay.
5.
Defective power exhauster motor.
Figure 53.2 - Flame Rollout Appearance
5-594.10
Possible Remedy
1.
Increase primary air.
2.
Adjust to a maximum of 14" W.C.
3.
Check orifice size with those listed on the
serial plate.
4.
Clean louvers in vent cap.
1.
Adjust to a maximum of 14" W.C.
2.
Check orifice size with those listed on the
serial plate.
3.
Clean louvers in vent cap.
1.
a. Clean/correct duct system.
b. Adjust to a maximum of 14" W.C.
c. Check that blower motor operates
within 45 seconds of when gas controls
are energized.
d. Adjust belt tension.
e. Check/correct blower drive settings for
proper rpm.
f. Check/correct venting system.
g. Replace high limit switch.
2.
Adjust main gas pressure. (Minimum for
Natural Gas — 6" W.C. Minimum for
Propane Gas — 11" W.C.)
3.
Adjust outside air damper to decrease
outside air percentage (if possible).
4.
Check/replace thermostat.
5.
Check unit wiring against the wiring
diagram.
6.
Check design conditions. If unit is under-
sized, an additional unit(s) or other heat
source must be added.
1.
Check/replace thermostat.
2.
a. Check unit wiring against the wiring
diagram.
b. Check for loose or worn wires.
3.
Adjust to a maximum of 14" W.C.
4.
Replace gas valve.
1.
Turn on main power.
2.
Check control transformer.
3.
Check/replace thermostat.
4.
Replace power exhauster relay.
5.
Replace power exhauster motor.
53
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