Ignition Lockout - Carrier 58MVP Troubleshooting Manual

STEP
36. Does fault occur after blower stops?
Increase blower off delay time to 225 sec by putting both setup switches SW-7
37.
and SW-8 in ON position.
Does furnace have proper limit switch, limit shield, blower baffle (if used), rear
38. air baffle (if used), and auxiliary limit switch? If so, are limit switch, limit shield,
and heat exchangers properly aligned?
Change limit switch first. If problem still exists, replace auxiliary limit switch.
39.
One of these switches is out of calibration.
40. Does fault occur during low fire?
On the third burner cycle, unit will run in high-fire mode and flash fault code
continuously. The unit is locked into high-fire-only mode. Verify the following
before going to Step 10:
• If unit has a bypass humidifier, make sure setup switch SW-3 is in ON po-
41. sition.
• If unit is installed in a zone system, make sure setup switch SW-5 is in
ON position.
• Check low-fire rate. Clock input rate. DO NOT use manifold pressure
method unless using propane.
Verify the following before going to Step 10:
• If unit is installed in a zone system, make sure setup switch SW-5 is in
42. ON position.
• Check high-fire rate. Clock input rate. DO NOT use manifold pressure
method unless using propane.
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
Turn power off, remove blower access panel, and disconnect R thermostat lead
1.
from furnace control board.
Turn power on and depress door switch. Use a piece of tape to hold switch
2.
closed.
Make sure thermostat is NOT calling for heat and reconnect R thermostat lead
3. 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. Replace furnace control board. Make sure it has a date code 9405 or later.
Disconnect R thermostat lead from furnace control board and jumper R and
5.
W/W1 thermostat terminals on furnace control board.
6. Observe operation of furnace through 1 heating cycle.
7. Does fault occur again?
8. Does a different fault occur?
9. Go to page number indicated in Index for fault code flashed.
Disconnect jumper wire across R and W/W1 thermostat terminals. Does fault
10.
occur now?
11. Replace gas valve.
Go to page number indicated in Index for CLEANUP AND START-UP
12.
INSTRUCTIONS.
Turn power off and disconnect jumper wire across R and W/W1 thermostat ter-
13.
minals.
14. Turn power on and wait several sec before proceeding to next step.
Check hot surface ignitor. To do this, put setup switch SW-6 for COMPONENT
15. TEST in ON position. Does ignitor glow orange/white hot by end of 15-sec
warm-up period?
Disconnect PL4 from furnace control board. Connect an AC voltmeter across
PL4-1 and PL4-2 on furnace control board. Repeat COMPONENT TEST by
16.
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?
17. Replace furnace control board.
18. Check continuity in harness and ignitor. Replace defective component.
25
YES NO GO TO
37 9 —
— — 27
39 27 —
— — 9
41 42 —
— — 10
— — 10
YES NO GO TO
— — 2
— — 3
4 5 —
— — 12
— — 6
— — 7
13 8 —
9 10 —
— — INDEX
11 12 —
— — 12
— — INDEX
— — 14
— — 15
20 16 —
18 17 —
— — 12
— — 19