Carrier 58MVP - Manual (Page 26)

Fault Code 34
IGNITION PROVING FAULT—This fault can indicate 1 of the following:
• Flame was not sensed during trial for ignition period. The control will repeat ignition sequence 3 more times before going into Fault
14—IGNITION LOCKOUT.
• The flame signal was lost after trial for ignition period.
• The flame signal was sensed while gas valve was de-energized. The inducer will run at full speed until fault is cleared.
STEP ACTION YES NO GO TO
1.
Turn power off, remove blower access panel, and disconnect R thermostat lead from furnace con-
trol board.
— — 2
2. Turn power on and depress door switch. Use a piece of tape to hold switch closed. — — 3
3.
Make sure thermostat is NOT calling for heat and reconnect R thermostat lead to furnace control
board. Observe unit for 15 minutes. Does inducer motor ever turn on at full speed while furnace
control board flashes Fault Code 34?
4 5 —
4. Replace furnace control board. Make sure it has a date code 9405 or later. — — 12
5.
Disconnect R thermostat lead from furnace control board and jumper R and W/W1 thermostat termi-
nals on furnace control board.
— — 6
6. Observe operation of furnace through 1 heating cycle. — — 7
7. Does fault occur again? 13 8 —
8. Does a different fault occur? 9 10 —
9. Go to page number indicated in Index for fault code flashed. — — INDEX
10. Disconnect jumper wire across R and W/W1 thermostat terminals. Does fault occur now? 11 12 —
11. Replace gas valve. — — 12
12. Go to page number indicated in Index for CLEANUP AND START-UP INSTRUCTIONS. — — INDEX
13. Turn power off and disconnect jumper wire across R and W/W1 thermostat terminals. — — 14
14. Turn power on and wait several sec before proceeding to next step. — — 15
15.
Check hot surface ignitor. To do this, put setup switch SW-6 for COMPONENT TEST in ON posi-
tion. Does ignitor glow orange/white hot by end of 15-sec warm-up period?
20 16 —
16.
Disconnect PL4 from furnace control board. Connect an AC voltmeter across PL4-1 and PL4-2 on
furnace control board. Repeat COMPONENT TEST by turning setup switch SW-6 OFF and then
back ON. Do you see 120 vac across PL4-1 and PL4-2 during 15-sec warm-up period?
18 17 —
17. Replace furnace control board. — — 12
18. Check continuity in harness and ignitor. Replace defective component. — — 19
19. Fix problem. — — 8
20. Put setup switch SW-6 for COMPONENT TEST in OFF position. — — 21
21. Jumper R and W/W1 thermostat terminals on furnace control board. — — 22
22.
Connect an AC voltmeter across BLUE and GREEN wires to gas valve GV. Does gas valve GV re-
ceive 24v?
26 23 —
23. Turn power off. — — 24
24.
Do you have continuity across the following connections:
• PL1-2 and BLUE wire at gas valve GV.
• PL1-7 and GREEN wire at gas valve GV. 17 25 —
25.
The BLUE or GREEN wire from furnace control board to gas valve GV is not making good connec-
tion. Repair wire(s) or replace harness.
— — 12
26. Does gas valve open and allow gas to flow? 28 27 —
27. Are all manual gas cocks in ON position? 11 19 —
28. Do main burners ignite? 30 29 —
29.
Check for the following:
• Inadequate flame carryover or rough ignition.
• Low inlet gas pressure. — — 19
30. Do main burners stay on? 40 31 —
31. Turn power off and disconnect jumper wire across R and W/W1 thermostat terminals. — — 32
32. Connect a DC microammeter in series with flame sensor wire. — — 33
33.
Turn power on and wait several sec then jumper R and W/W1 thermostat terminals on furnace con-
trol board.
— — 34
34. Is DC current below 0.5 microamps? 36 35 —
35.
Check connections and recheck current. If current is near typical value and control will not stay on,
replace furnace control board.
— — 12
36.
Clean flame sensor with fine sandpaper and recheck current. Current is typically 4.0 to 6.0 micro-
amps.
— — 37
37. Is current near typical value? 39 38 —
38. Replace electrode. — — 12
39. Will main burners ignite and stay on? 12 17 —
40. Do you have combustion pulsations? 41 47 —
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