Fault code 33 – Carrier 58MVP User Manual
Page 24
29.
Is inducer blower wheel okay?
31
30
—
30.
If possible, replace inducer blower wheel. Otherwise, replace inducer motor assembly.
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—
10
31.
Is there any frost build-up on combustion-air inlet?
32
33
—
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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—
27
33.
You have excessive restriction in combustion-air or vent pipe.
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—
10
34.
The problem is either a sag in vent pipe or a clogged drain trap or line.
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—
27
35.
Turn power off and disconnect jumper wire across R and W/W1 thermostat terminals.
—
—
36
36.
Turn power on and wait several sec, then jumper R and W/W1 thermostat terminals on furnace con-
trol board.
—
—
37
37.
Do you have 24v between connector terminal PL2-2 and Com on furnace control board when fault
occurs?
13
38
—
38.
Turn power off.
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—
39
39.
Do you have continuity across terminal PL2-2 and N.O. (Normally Open) contact on low-pressure
switch LPS?
16
40
—
→
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.
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—
27
41.
Turn power off and disconnect jumper wire across R and W/W1 thermostat terminals.
—
—
42
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.
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—
43
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
44.
Monitor slope manometer. Does pressure reading appear to be stable when fault occurs?
45
46
—
45.
Replace pressure switch assembly. If problem persists, check wiring for an intermittent connection
in low-pressure switch LPS circuit.
—
—
10
46.
Check for a sag in vent pipe. If problem persists, replace inducer motor.
—
—
10
47.
Do you have 24v between connector terminal PL2-2 and Com on furnace control board?
48
13
—
48.
The main harness is miswired.
—
—
27
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)
26
13
—
50.
Does inducer motor MTR1 turn on?
19
51
—
51.
Do you have less than 90 vac between
I
1 and
I
2 on furnace control board?
53
52
—
52.
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)
26
13
—
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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—
27
→
54.
Does the fault occur before ignition 45 sec after call for heat?
50
41
—
→
55.
Check propane line pressure if using low gas pressure switch LGPS otherwise go to step 41.
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—
27
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
NO
GO TO
1.
Turn power off, remove blower access panel, and disconnect R thermostat lead.
—
—
2
2.
Turn power on and depress door switch. Use a piece of tape to hold switch closed.
—
—
3
3.
Is the fault code flashing?
11
4
—
4.
Set thermostat to call for heat or jumper R and W/W1 thermostat terminals.
—
—
5
5.
Observe operation of furnace for next 25 minutes.
—
—
6
6.
Does fault occur again?
40
7
—
7.
Does a different fault occur?
8
9
—
8.
Go to page number indicated in Index for fault code flashed.
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INDEX
24