Carrier 48DL Installation Manual download pdf (Page 83)

264975-BIM-B-1208

Johnson Controls Unitary Products 83

9. If the blower motor runs with the fan switch in the “ON”

position but does not run shortly after the furnace has

ignited when the fan switch is in the “AUTO” position,

check the room thermostat for contact between R and G

during “W1” calls.

On calls for heating, the supply air blower operates but the

draft motor does not (the room thermostat fan switch is in the

“AUTO” position).

1. The draft motor has inherent protection. If the motor

shell is hot to the touch, wait for the internal overload to

reset.

2. If the motor shell is cold with the room thermostat calling

for heat, check for line voltage at the motor leads. If line

voltage is present, replace the draft motor.

3. If line voltage is not present, check for line voltage on the

ignition control at the “inducer” terminal draft motor relay

(DMR or DMC) contacts in the main control box and

check to see if the (DMR or DMC) is pulled in.

The draft motor runs but the furnace does not light and the

spark ignitor does not spark.

1. Check for 24 volts at the spark ignitor from the ignition

control board (ICB). Check the 24-volt wiring from the

ICB to the spark ignitor. Check for 24 volts at the ICB

spark ignitor terminal.

2. Check the ground wiring for the ICB and the gas valve is

intact and making good electrical connection. Check the

ceramic insulator on the spark ignitor for breaks or

cracks. Replace the spark ignitor if damaged.

3. With the draft motor running, check for 24 volts at the

pressure switch terminal on the ICB. If not present,

check for 24 volts on the terminal from the pressure

switch. If present, go to step 4. If 24 volts is not present,

the either pressure or rollout switch is not closed. Or the

draft motor is not sufficiently evacuating the heat

exchanger tubes or the pressure switch has failed.

Check the operation of the pressure switch. Check the

line voltage to the unit; if line voltage is low, call the local

power company. If the problem persists, the draft motor

may need replacement.

4. If the furnace is hot, it may be out on a high temperature

limit open; wait for limit reset.

5. If all are intact replace the ICB.

The draft motor runs and the spark ignitor sparks at the

burner, but the burner does not ignite and a gas odor is not

detected at the draft motor outlet.

1. Check to ensure gas is being supplied to the unit. Con-

firm that the gas pressure to the unit is within the proper

limits as described in the “POST START CHECKLIST”.

2. Check the voltage at the gas valve and at the gas valve

terminals on the ICB. Check all wiring between the ICB

and the gas valve. Check to make sure the ground con-

nections are intact.

3. If 24 volts is present, remove the pilot burner and the ori-

fice. The removal procedure is described in

“BURNER/ORIFICE INSPECTION/SERVICING.” Inspect

the orifice for obstruction. If it is clear, replace the gas

valve.

Main burners light but exhibit erratic flame characteristics.

1. Check the main burner orifices for obstruction and align-

ment. The removal procedure is described in

“BURNER/ORIFICE INSPECTION/SERVICING”. Clean

or replace burner orifices and burners as needed.

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Carrier 48DL Installation Manual Page 83

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