29. Is inducer blower wheel okay? 31 30 —
30. If possible, replace inducer blower wheel. Otherwise, replace inducer motor assembly. — — 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.
—— 27
33. You have excessive restriction in combustion-air or vent pipe. — — 10
34. The problem is either a sag in vent pipe or a clogged drain trap or line. — — 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. —— 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.
—— 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.
—— 43
43.
Turn power on and wait several sec, then jumper R and W/W1 thermostat terminals on furnace con-
trol board.
—— 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 I1 and I2 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.
—— 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. — — 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? 89 —
8. Go to page number indicated in Index for fault code flashed. — — INDEX
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