WARNING: Troubleshooting of components necessarily re-quires opening the electrical control box with thepower connected to the unit. Use extreme carewhen working with live circuits! Check the unitnameplate for the correct line voltage and set thevolt meter to the correct range before making anyconnections with line terminals.WARNING: Prior to any of the following maintenance proce-dures, shut off all electric power to the unit toprevent personal injury.CAUTION: Label all wires prior to disconnection when servic-ing controls. Wiring errors can cause improper anddangerous operation. Verify proper operation afterservicing.NOTE To find the Btu input, multiply the number of cubic feet ofgas consumed per hour by the Btu content of the gas inyour particular locality (contact your gas company for thisinformation - it varies widely from city to city.)1. Draft motor operates and furnace lights but supply airblower does not start after a short time delay with roomthermostat fan switch set to “AUTO”.a. Set fan switch to “ON”. If blower motor runs, go to Step f.If it does not, check to see if line voltage is beingsupplied to the contacts of the contactor (M3), and if thecontactor is pulled in. Check for loose wiring.b. If (M3) is pulled in, touch the supply air blower motorhousing. If it is hot, the motor may be off on inherentprotection. Disconnect power to the unit and check theblower motor capacitor. If it is defective, replace it withone of equal capacitance and voltage.c. If (M3) is pulled in and the blower motor still does notrun, replace the blower motor.d. If (M3) is not pulled in, check for 24 volts at the (M3) coil.If 24 volts is present, replace the (M3) contactor.e. If 24 volts is not present at the (M3) coil, check for loose24 volt wiring back to the relay board. Check controlwiring to the room thermostat. If all is fine, replace therelay board.f. If the blower motor runs with the fan switch in the “ON”position but does not run soon after the furnace hasignited with the fan switch in the “AUTO” position, checkfor loose 24 volt wiring between the relay board in themain control box, the Mate-N-Lok connector in thepartition between the evaporator and gas heat sectionsand the time delay (BT) or (ETD).g. If all control wiring is fine, check for 24 volts at the relayboard. If 24 volts is present, replace the relay board. If24 volts is not present, replace the (BT) or (ETD).NOTE: The furnace may shut itself down on a high tempera-ture condition during the procedure, but this will noteffect the test if it is done within 5 minutes of furnaceshut-down.2. The supply air blower operates but the draft motor does notwhen the room thermostat is set to call for heat and the fanswitch in the “ON” position.a. The draft motor has inherent protection. If the motor shellis hot to the touch, wait for the internal overload to reset.b. If the motor shell is cold with the room thermostat callingfor heat, check for line voltage at the motor’s Mate-N-Lok connector attached to the evaporator partition. Ifline voltage is present, replace the draft motor.c. If line voltage is not present, check for line voltage atthe draft motor relay (DMR or DMC) contacts in the maincontrol box and check to see if the (DMR or DMC) ispulled in.d. If the (DMR or DMC) relay is pulled in, check for a looseline voltage connection.e. If the (DMR or DMC) relay is not pulled in, check for 24volts at the (DMC) coil or 24 V at the DMC-6 terminal.If 24 volts is present, replace the (DMR or DMC) relay.If 24 volts is not present, check for a loose 24 voltconnection back to the relay board and check theconnections from the room thermostat to the relayboard. If all connections are correct, replace the relayboard.3. The draft motor runs but the furnace does not light and thesparker does not spark.a. Check all 24 volt connections from the relay board toand in the gas heat section. Check low voltage connec-tions to the(BT) & (DMC) or (ETD) located in the controlbox.b. If the furnace is hot, it may be out on an over tempera-ture condition, wait for limit reset.c. With the draft motor running, check for 24 volts atterminal 25V on the ignitor control (IC) where the redlead from the draft motor attaches. If 24 volts is notpresent, the centrifugal switch (CS) has not closed orhas gone bad. Check the line voltage to the unit, if it iscorrect replace the draft motor. If line voltage is low callthe power company.d. If 24 volts is present at the ignitor control, check allcontrol wiring at the ignitor control and the high tensionwire to the ignitor. Check that the green ground wiresfrom the ignitor control, the gas valve and pilot burnerare all intact and making good electrical connection.Check to make sure that the ceramic insulator on thepilot ignitor or sensor is not broken or cracked, if all areintact replace the ignition control “IC”.4. The draft motor runs and the sparker sparks at the pilotburner but the pilot does not ignite and a gas odor is notdetected at the draft motor outlet.a. Check to make sure gas is being supplied to the unit.Make sure that the gas pressure to the unit is within theproper limits as described in the “POST START CHECKTROUBLESHOOTING530.18-N10YUnitary Products Group 19