Fault code 33 – Carrier 58MVP User Manual

Page 24

29.

Is inducer blower wheel okay?

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30.

If possible, replace inducer blower wheel. Otherwise, replace inducer motor assembly.

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31.

Is there any frost build-up on combustion-air inlet?

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32.

The problem is caused by reversed vent and combustion-air pipes or some other moist air entering
combustion-air pipe.

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33.

You have excessive restriction in combustion-air or vent pipe.

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34.

The problem is either a sag in vent pipe or a clogged drain trap or line.

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35.

Turn power off and disconnect jumper wire across R and W/W1 thermostat terminals.

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36.

Turn power on and wait several sec, then jumper R and W/W1 thermostat terminals on furnace con-
trol board.

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37.

Do you have 24v between connector terminal PL2-2 and Com on furnace control board when fault
occurs?

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38.

Turn power off.

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39.

Do you have continuity across terminal PL2-2 and N.O. (Normally Open) contact on low-pressure
switch LPS?

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→

40.

The ORANGE wire from low-pressure switch LPS to furnace control board is not making good con-
nection or low gas pressure switch LGPS (when used) is open. Check propane line pressure if us-
ing LGPS otherwise repair wire or replace harness.

—

41.

Turn power off and disconnect jumper wire across R and W/W1 thermostat terminals.

—

42.

Connect 1 side of a slope manometer with a tee to collector box pressure tap. Connect other side
with a tee to gas valve air pressure fitting. Refer to pressure check diagram in Appendix C.

—

43.

Turn power on and wait several sec, then jumper R and W/W1 thermostat terminals on furnace con-
trol board.

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44.

Monitor slope manometer. Does pressure reading appear to be stable when fault occurs?

—

45.

Replace pressure switch assembly. If problem persists, check wiring for an intermittent connection
in low-pressure switch LPS circuit.

—

46.

Check for a sag in vent pipe. If problem persists, replace inducer motor.

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47.

Do you have 24v between connector terminal PL2-2 and Com on furnace control board?

—

48.

The main harness is miswired.

—

49.

Check Inducer PW line. To do this, disconnect PL7 from inducer motor and connect a DC voltmeter
across terminals PL7-2 BROWN (+) and PL7-10 YELLOW (-) then run COMPONENT TEST by
turning setup switch SW-6 ON. Does voltage across PL7-2 and PL7-10 change between states as
shown below?

• State 1—OFF (-0.1 — 0.1 vdc)
• State 2—LOW (6.0 — 7.0 vdc)
• State 3—HIGH (10.5 — 11.5 vdc)

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50.

Does inducer motor MTR1 turn on?

—

51.

Do you have less than 90 vac between

1 and

2 on furnace control board?

—

52.

• State 1—OFF (-0.1 — 0.1 vdc)
• State 2—LOW (6.0 — 7.0 vdc)
• State 3—HIGH (10.5 — 11.5 vdc)

—

53.

Make sure wire gage between main fuse box and furnace complies with wire size specification in
Installation, Start-Up, and Operating Instructions.

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54.

Does the fault occur before ignition 45 sec after call for heat?

—

→

55.

Check propane line pressure if using low gas pressure switch LGPS otherwise go to step 41.

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Fault Code 33

LIMIT SWITCH FAULT—This fault indicates the limit switch, rollout switch or auxiliary limit switch is open or
unit is operating in high-heat only mode due to 2 successive low-heat limit trips.

STEP

ACTION

YES

GO TO

Turn power off, remove blower access panel, and disconnect R thermostat lead.

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

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Is the fault code flashing?

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Set thermostat to call for heat or jumper R and W/W1 thermostat terminals.

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Observe operation of furnace for next 25 minutes.

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Does fault occur again?

—

Does a different fault occur?

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Go to page number indicated in Index for fault code flashed.

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INDEX