Carrier 59MN7A Troubleshooting Guide download pdf (Page 27)

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Status Code 33

LIMIT CIRCUIT FAULT - This status code indicates the limit, flame rollout switch is open, or the furnace is operating in

maximum-heat only mode due to 2 successive limit trips while operating at any rate <

71% of maximum rate. Blower will run

for 4 minutes at intermediate heat airflow or until the open switch remakes whichever is longer. If open longer than 3 minutes,

code changes to lockout #13. If open less than 3 minutes status code #33 continues to flash until blower shuts off. Flame

rollout switch requires manual reset.

STEP ACTION YES NO GO TO

1. Turn power off, remove blower door, and disconnect User Interface ABCD connector (if used)

or the R thermostat lead (if used) from the furnace control board. Note current setting of setup

switch SW4-2 and then set it to the ON position.

2. Turn power on and depress door switch. Use a piece of tape to hold switch closed. 3

3. Does status code 33 flash? 11 4

4. Does a different status code flash? 5 6

5. Return setup switch SW4-2 to its original setting and go to page number indicated in the Index

for the section covering the status code.

INDEX

6. Jumper R and W/W1 thermostat terminals. 7

7. Observe the furnace operation for 15 minutes or until status code starts flashing. 8

8. Does status code 33 flash? 39 9

9. Does a different status code flash? 5 27

10. Return setup switch SW4-2 to its original setting and go to page number indicated in Index for

CLEANUP AND START-UP INSTRUCTIONS.

INDEX

11. Is 24-vac across connector terminal PL1-6 and COM-24V on modulating furnace control? 13 12

12. Replace the modulating furnace control. 10

13. Is 24-vac across connector terminal PL1-8 and COM-24V on modulating furnace control? 12 14

14. Turn power off. 15

15. Do you have continuity across limit switch LS? 19 16

16. Wait for unit to cool then recheck for continuity across limit switch LS. 17

17. Do you have continuity across limit switch LS? 19 18

18. Replace limit switch. 10

19. Do you have continuity across both flame rollout switch(es) FRS? 35 20

20. Can open flame rollout switch FRS be reset? 22 21

21. Replace flame rollout switch FRS. 10

22. Reset flame rollout switch FRS, turn power on, and observe furnace operation for (2) 15

minute cycles.

23. Does flame rollout switch FRS trip again? 25 24

24. Does a different status code flash? 5 10

25. You have inadequate combustion-air supply. This may be caused by:

- Reversed vent and combustion-air pipes.

- Poor burner, manifold, or orifice alignment.

- Blocked heat exchanger.

- Leak in secondary heat exchanger.

- Leak somewhere between primary and secondary heat exchangers.

- Leak between vestibule and blower compartment.

- Flue gas leak in vestibule.

26. Fix problem. 10

27. While the unit is operating in intermediate heat jumper R and W2. 28

28. Observe furnace operation for another 10 minutes or until status code 33 starts flashing. 29

29. Does status code 33 flash? 50 30

30. Does a different status code flash? 5 31

31. Is the furnace in the downflow or horizontal position? 32 68

32. Disconnect the R thermostat lead, wait for blower to stop, and continue to observe furnace for

5 minutes.

33. Does fault occur after blower stops? 34 10

34. Increase the blower off-delay time to 180 seconds by putting both setup switches SW1-7 and

SW1-8 into the ON position.

35. Turn power on. 36

36. Does status code 33 flash? 38 37

37. Does a different status code flash? 5 6

38. You have an open RED wire or bad terminal in limit circuit. Repair wire or replace harness. 10

39. Does furnace have the proper limit switch, and is the limit gasket installed? If so, are the heat

exchangers properly aligned?

40 26

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Carrier 59MN7A Troubleshooting Guide Page 27

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