Carrier 58MCA - Page 17

Fig. 20—Troubleshooting Guide for 58MCA and 58MXA
A93258
A93258b
11 NO PREVIOUS FAULT - Faults
are erased after 48 hrs or whenever power (115v or 24v) is interrupted. Run system through a heating or cooling cycle to  check system.
12 BLOWER ON AFTER POWER
UP (115V OR 24V) - Normal  operation. Blower will run for 90 sec when furnace power is interrupted during a call for heat, R-W closed.
13 LIMIT OR FLAME ROLLOUT
SWITCH LOCKOUT - Limit switch was open longer than 3 minutes. Auto-reset will occur after 3 hrs. Flame rollout switch requires manual reset. See No. 33
14 IGNITION LOCKOUT - System
failed to ignite gas and prove flame in 4 attempts. Control will auto-reset in 3 hrs. See No. 34
21 GAS HEATING LOCKOUT - 
Turn off power and wait 5 minutes to retry. Check for:
Unplug ignitor harness from control center and inititate another  component test sequence. Check for 115v between pins 1 and 2 on the control center. Was 115v present for the 17-sec period?
Replace control center.
Check for continuity in the harness and ignitor. Replace defective component.
Reconnect the R thermostat lead and set thermostat to call for heat. Connect voltmeter across gas valve connections. Does gas valve receive 24v?
Check connections. If OK, replace control center.
Does gas valve open and allow gas to flow?
Check that all gas valves are turned on. Replace valve.
Do main burners ignite? Do main burners stay on? Allow blower to come on and repeat test to check for intermittent operation.
Repeat call for heat and check flame sensor current during trial for ignition period. Is the DC microamps below 0.5?
Check connections and retry. If  current is near typical value and control will not stay on, replace control center.
Clean flame sensor with fine sandpaper and recheck current.  Current is nominally 4.0 to 6.0 microamps. Is current near typical value?
Replace electrode.
Will main burner ignite and stay on?
Replace control center.
Fixed.
• Stuck closed gas valve relay
on control.
• Miswire or short to gas valve
wire.
22 ABNORMAL FLAME PROVING
SIGNAL - Flame was sensed while gas valve was de-energized. Inducer will run until fault is cleared. Check for:
• Stuck open gas valve solenoid
or leak.
• Defective control center.
23 PRESSURE SWITCH WILL
NOT OPEN - Check for:
• Disconnected or obstructed
pressure tubing.
• Defective pressure switch.
24 LOW-VOLTAGE FUSE IS
OPEN - Check for:
• Short in low-voltage wiring
including thermostat leads shorting to ductwork or furnace cabinet. Disconnect thermostat leads to isolate short circuit.
31 PRESSURE SWITCH WILL
NOT CLOSE OR REOPEN - If open longer than 5 minutes, inducer shuts off for 15 minutes before retry.  Check for:
• Proper vent sizing or pitch or
sag.
• Vent restrictions or high winds. • Defective inducer motor. • Low line voltage (115v). • Motor start capacitor. • Low inlet gas pressure. • Defective pressure switch or
connections. If it opens after trial for ignition period, blower will come on for 90 sec recycle delay.
• Inadequate combustion air.
33 LIMIT OR FLAME ROLLOUT 
SWITCH IS OPEN - If  limit switch is open longer than 3 minutes, code changes to No. 13. Check for: • Blower motor failure. • Motor start capacitor. • Open flame rollout switch, 
manual reset.
• Dirty filter. • Defective limit switch or 
connections.
• Loose blower wheel.
34 IGNITION PROVING FAILURE -
If flame is not sensed during the trial for ignition period, the control will repeat the ignition sequence 3 more times before going into lockout, No. 14. If flame signal is lost after trial for ignition period, blower will come on for 90-sec recycle delay. Check for the following items first before proceding to the next step. • Gas valve turned off. • Manual shut-off valve. • Green wire must be connected
to furnace sheet metal.
To determine whether the problem is in the gas valve, ignitor, or flame sensor, the system can be operated in the component test mode to check the ignitor. First, remove the R thermostat connection from the control center and initiate the component test sequence. Does the ignitor glow orange/white hot by the end of the 17-sec warm-up period?
Check for:
• Inadequate flame carryover on
rough ignition.
• Low inlet gas pressure.
NO
YES
YES YES YES YES YES
YES YES YES
NO NO
NO NO NO NO NO
•
Inadequate combustion air  supply (flame rollout switch only).
NO
17