Carrier 48KHA - Manual (Page 22)

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 con­
nection 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 main­
tain 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 com­
partment — 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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