Carrier 48NLT Installation, Start-up And Service Instructions Manual

Also see for 48NET: Installation, Start-Up and Service Instructions

Table 11 — Heating Troubleshooting ChartSYMPTOM CAUSE REMEDYIGN locked out. LED flashing I Look for problems external to the ignitor module.LED glowing continuously 1 Replace IGN control.Pilot wHi not light. No spark at electrode Check air gap between electrode tip and pilot targetGap should be as shown in Fig. 15.Readjust as necessary.Clean moisture or dirt accumulation on electrode ceramic with' cloth.Cracked ceramic — replace pilot electrode assemblyCheck for loose or broken wiring at and between electroniccontrol head and electrode Replace wire or tighten connectionas necessary.! Check fuses or circuit breaker to ensure voltage to unit.! Check for 24 v between TH and COM. If you read 24 v andabove steps have been completed, replace electronic ignition; control.Spark shorting out to main burner 1 Realign electrode tip away from main burner but maintain1 spark gap to pilot burner. See Fig. 15.No gas at pilot burner Clean pilot orifice.1 Check inlet pressure to gas value. Recommended operatingpressure 7-in. wg natural gas, 11-in. wg LP gas; 0.5 psig (13.6-in. wg) max. pressureCheck for 24 v between terminals PV and COM If you read 24V and above steps have been completed, replace gas valve.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-v 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 v between terminals MV and COM on controlhead If you read 24 v, replace gas valve portion of controlhead/gas valve assembly.2. If 24 V is not present, check flame sensor for cracked ce¬ramic insulator or shorted sensor cable.Broken thermostat wire Run continuity check to locate break.Inadequate heating. Dirty air filter Clean or replace fitter as necessary.Gas input to furnace too low Check gas pressure at manifold. Clock gas meter for input. Iftoo low, increase manifold pressure, or replace with correctorifices.Unit undersized for application Replace with proper unit — or add additional unitRestricted airflow Clean or replace filter — or remove any restriction.Blower speed too low Use faster speed tapCheck temperature rise.Limit switch cycles main burners Dirty air filters — clean or replace.Registers closed, restricted ductwork — open or removerestriction.Check temperature rise.Check heat anticipator setting on thermostat — readjust.Poor flamecharacteristics.1incomplete combustion results in;Aldehyde odors, CO, sooting flame —floating flameCheck all screws around flue outlets and burner compartment— tighten.LACK OF COMBUSTION AIR.Cracked heat exchanger — replace.Overfired furnace — reduce input, or change orifices.Check vent for restriction — clean as requiredCheck orifice for burner alignment.GR — GroundLP — Liquid Propane21