Carrier 48KHA - Manual (Page 20)

TROUBLESHOOTING CHART
Table 9—Heating Service Analysis Chart
SYMPTOM PROBABLE CAUSE REMEDY
Pilot will not light No spark at electrode Check air gap between electrode tip and pilot burner Gap should be
as shown in Fig. 11. Readjust as necessary.
Clean moisture or dirt accumulation on electrode ceramic with cloth.
Cracked ceramic—replace pilot electrode assembly.
Check for loose or broken wiring at and between spark generator and
electrode. Replace wire or tighten connection as necessary.
Check fuses or circuit breaker to ensure voltage to unit.
Check 24-volt input to spark generator. If reading is 24 volts, and
above steps have been completed, replace electronic control head
portion of control head/gas valve assembly.
Spark shorting out to main burner Realign electrode tip away from main burner but maintain spark gap
to pilot burner. See Fig. 11.
No gas at pilot burner Clean pilot orifice.
Check for 24 volts between terminals no. 1 and GR of gas valve. If
reading is 24 volts, and above steps have been completed, replace gas
valve portion of control head/gas valve assembly.
Burners will not ignite Water in gas line Drain—install water trap.
No power to furnace Check power supply, fuses, wiring, or circuit breaker.
No 24-volt power supply to control circuit Check transformer—replace If necessary.
Miswired or loose connections Check all wiring and wirenut connections.
Dirty pilot—yellow flame Clean pilot orifice.
Pilot burning improperly—
sharp blue flame
Replace pilot
Burned-out heat anticipator in thermostat Replace thermostat.
No gas at main burners 1. Check for 24 volts between terminals 3 and GR on control head If
reading is 24 volts, replace gas valve portion of control head/gas
valve assembly
2 If reading is not 24 volts, check flame sensor for cracked ceramic
insulator or shorted sensor cable Replace electronic head if
sensor circuit is not defective.
Broken thermostat wire Run continuity check to locate break.
Inadequate heating Dirty air filter Clean or replace filter as necessary.
Gas input to furnace too low Check gas pressure at manifold Clock gas meter for input If too low,
increase manifold pressure, or replace with correct orifices.
Unit undersized for application Replace with proper unit—or add additional unit.
Restricted airflow Clean or replace filter—or remove any restriction.
Blower speed too low Use faster speed tap—or install optional blower.
Limit switch cycles main burners Dirty air filters—clean or replace.
Registers closed, restricted ductwork—open or remove restriction.
Check heat anticipator setting on thermostat—readjust.
Poor flame characteristics Incomplete combustion results in:
Aldehyde odors, (CO), sooting flame—
floating flame
Air shutters on burners closed—adjust to soft blue flame.
Check all screws around flue outlets and burner compartment—
tighten.
Lack of combustion air. See Installation section.
Cracked heat exchanger—replace.
Overfired furnace—reduce input, or change orifices.
Check vent for restriction—clean as required.
Check orifice to burner alignment.
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