Carrier 48KH - Manual (Page 22)

TROUBLESHOOTING CHART
Table 8 — Heating Service Analysis Chart
SYMPTOM
Pilot will not light
Burners will not ignite
Inadequate heating
PROBABLE CAUSE
No spark at electrode
Spark shorting out to main burner
No gas at pilot burner
REMEDY
Water in gas line
No power to furnace
No 24-volt power supplytocontrol
circuit
Miswired or loose connections
Dirty pilot — yellow flame
Pilot burning improperly — sharp
blue flame
Burned-out heat anticipator in
thermostat
No gas at main burners
Broken thermostat wire
Poor flame characteristics
Dirty air filter
Gas input to furnace too low
Unit undersized for application
Restricted airflow
Blower speed too low
Limit switch cycles main burners
Incomplete combustion results in:
Aldehyde odors, (CO), sooting
flame — floating flame
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 you read 24
volts, and above steps have been completed, replace
spark generator
Realign electrode tip away from main burner but main­
tain spark gap to pilot burner See Fig 11
Clean pilot orifice.
Check for voltage to terminals no. 3 and 5 of gas valve.
Check to see if pilot valve is opening Check for loose or
broken wiring connections If no deficiency is found,
replace gas valve
Drain — install water trap
Check power supply, fuses, wiring, or circuit breaker
Check transformer — replace if necessary.
Check all wiring and wirenut connections
Clean pilot orifice
Replace pilot
Replace thermostat.
Check to see if main gas valve is opening Look for loose
or broken wiring connections If no deficiency is found,
replace valve assembly
Run continuity check to locate break
Clean or replace filter as necessary
Check gas pressure at manifold Clock gas meter for
input If too low, increase manifold pressure, or replace
with correct orifices
Replace with proper unit — or add additional unit
Clean or replace filter — or remove any restriction
Use faster speed tap — or install optional blower.
Dirty air filters — clean or replace
Registers closed, restricted ductwork — open or remove
restriction
Check heat anticipator setting on thermostat — readjust
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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