TROUBLESHOOTING
10.After brushing is complete, blow all brushed areas with air or nitrogen. Vacuum as needed.
11.Replace parts in the order they were removed in Steps 1 thru 4.
12.When replacing the center and top of the flue collector box, be careful not to tear the adjoining insulation.
13.Ensure that all seams on the vent side of the combustion system are air tight. Apply a high temperature (+500° F) sealing compound where needed.
WARNING: Troubleshooting of components necessarily re- quires opening the electrical control box with the 
power connected to the unit. Use extreme care when working with live circuits! Check the unit nameplate for the correct line voltage and set the volt meter to the correct range before making any
connections with line terminals.
WARNING: Prior to any of the following maintenance proce- dures, shut off all electric power to the unit to prevent personal injury.
CAUTION: Label all wires prior to disconnection when servic- ing controls. Wiring errors can cause improper and dangerous operation. Verify proper operation after servicing.
NOTE: To find the Btu input, multiply the number of cubic feet of gas consumed per hour by the Btu content of the gas in your particular locality (contact your gas company for this information - it varies widely from city to city.)
1.The indoor blower motor is a
a.If the Indoor Blower Motor does not operate, check visually that contactor M3 is pulled in. If so, check for line voltage between all three phases at the line termi- nals of the Blower Overload Relay (BOR). If line voltage is found, check the leads to the blower motor for open circuit. If line voltage is found at the motor leads (inside the conduit box on the motor shell), disconnect the motor and check for open windings per the motor wiring diagram. If open windings are found, replace the motor. If line voltage is not found at the BOR, trace the leads back to the field supply terminal block, checking for an open circuit or blown fuses.
b.If the contactor M3 is not pulled in, check for control voltage (24V) at the M3 coil. If voltage is found, replace the contactor. If control voltage is not found at M3, check for voltage across terminals 95 & 96 of the BOR. If voltage exists, the BOR is open on overload. The BOR should be set to the auto reset position. The BOR must cool down in order to reset. If the BOR will not reset, replace the BOR. If the BOR resets and M3 pulls in, but the indoor blower motor will still not run, refer to para.
(a)for troubleshooting the line voltage supply circuit. If control voltage is not found at the BOR, trace the circuit back to the relay board and thermostat per the unit wiring diagram. Replace any defective components.
2.Draft motor operates and furnace lights but supply air blower does not start after a short time delay with room thermostat 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 being supplied to the contacts of the contactor (M3), and if the contactor is pulled in. Check for loose wiring.
b. If contactor (M3) is pulled in, proceed with the trou- bleshooting steps indicated in Step 1 above.
c.If (M3) is pulled in and the blower motor still does not run, 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 loose 24 volt wiring back to the relay board. Check control wiring to the room thermostat. If all is fine, replace the relay board.
f.If the blower motor runs with the fan switch in the “ON” position but does not run soon after the furnace has ignited with the fan switch in the “AUTO” position, check for loose 24 volt wiring between the relay board in the main control box, the
g.If all control wiring is fine, check for 24 volts at the relay board. If 24 volts is present, replace the relay board. If 24 volts is not present, replace the (ETD) relay.
NOTE: The furnace may shut itself down on a high tempera- ture condition during the procedure, but this will not effect the test if it is done within 5 minutes of furnace
3.The supply air blower operates but the draft motor does not when the room thermostat is set to call for heat and the fan switch in the “ON” position.
a.The draft motor has inherent protection. If the motor shell is hot to the touch, wait for the internal overload to reset.
b.If the motor shell is cold with the room thermostat calling for heat, check for line voltage at the motor’s
c.If line voltage is not present, check for line voltage at the heat relay (RW1) contacts in the main control box and check to see if the (RW1) is pulled in.
d.If the (RW1) relay is pulled in, check for a loose line voltage connection.
e.If the (RW1) relay is not pulled in, check for 24 volts at the (RW1) coil. If 24 volts is present, replace the (RW1) relay. If 24 volts is not present, check for a loose 24 volt connection back to the relay board and check the con- nections from the room thermostat to the relay board. If all connections are correct, replace the relay board.
Cont’d.
Unitary Products Group | 21 |
