Carrier Understanding Fault Codes: Troubleshooting Your Furnace

29.	Is inducer blower wheel okay?		31	30	Ð
30.	If possible, replace inducer blower wheel. Otherwise, replace inducer motor assembly.		Ð	Ð	10
31.	Is there any frost build-up on combustion-air inlet?		32	33	Ð
32.	The problem is caused by reversed vent and combustion-air pipes or some other moist air entering		Ð	Ð	27
	combustion-air pipe.
33.	You have excessive restriction in combustion-air or vent pipe.		Ð	Ð	10
34.	The problem is either a sag in vent pipe or a clogged drain trap or line.		Ð	Ð	27
35.	Turn power off and disconnect jumper wire across R and W/W1 thermostat terminals.		Ð	Ð	36
36.	Turn power on and wait several sec, then jumper R and W/W1 thermostat terminals on furnace con-		Ð	Ð	37
	trol board.
37.	Do you have 24v between connector terminal PL2-2 and Com on furnace control board when fault		13	38	Ð
	occurs?
38.	Turn power off.		Ð	Ð	39
39.	Do you have continuity across terminal PL2-2 and N.O. (Normally Open) contact on low-pressure		16	40	Ð
	switch LPS?
→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-		Ð	Ð	27
	ing LGPS otherwise repair wire or replace harness.
41.	Turn power off and disconnect jumper wire across R and W/W1 thermostat terminals.		Ð	Ð	42
42.	Connect 1 side of a slope manometer with a tee to collector box pressure tap. Connect other side		Ð	Ð	43
	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-		Ð	Ð	44
	trol board.
44.	Monitor slope manometer. Does pressure reading appear to be stable when fault occurs?		45	46	Ð
45.	Replace pressure switch assembly. If problem persists, check wiring for an intermittent connection		Ð	Ð	10
	in low-pressure switch LPS circuit.
46.	Check for a sag in vent pipe. If problem persists, replace inducer motor.		Ð	Ð	10
47.	Do you have 24v between connector terminal PL2-2 and Com on furnace control board?		48	13	Ð
48.	The main harness is miswired.		Ð	Ð	27
	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
49.	turning setup switch SW-6 ON. Does voltage across PL7-2 and PL7-10 change between states as
	shown below?		26	13	Ð
	·	State 1ÐOFF (-0.1 Ð 0.1 vdc)
	·	State 2ÐLOW (6.0 Ð 7.0 vdc)
	·	State 3ÐHIGH (10.5 Ð 11.5 vdc)
50.	Does inducer motor MTR1 turn on?		19	51	Ð
51.	Do you have less than 90 vac between I1 and I2 on furnace control board?		53	52	Ð
	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
52.	turning setup switch SW-6 ON. Does voltage across PL7-2 and PL7-10 change between states as
	shown below?		26	13	Ð
	·	State 1ÐOFF (-0.1 Ð 0.1 vdc)
	·	State 2ÐLOW (6.0 Ð 7.0 vdc)
	·	State 3ÐHIGH (10.5 Ð 11.5 vdc)
53.	Make sure wire gage between main fuse box and furnace complies with wire size specification in		Ð	Ð	27
	Installation, Start-Up, and Operating Instructions.
→54.	Does the fault occur before ignition 45 sec after call for heat?		50	41	Ð
→55.	Check propane line pressure if using low gas pressure switch LGPS otherwise go to step 41.		Ð	Ð	27

Fault Code 33

LIMIT SWITCH FAULTÐThis 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.	Ð	Ð	2
2.	Turn power on and depress door switch. Use a piece of tape to hold switch closed.	Ð	Ð	3
3.	Is the fault code flashing?	11	4	Ð
4.	Set thermostat to call for heat or jumper R and W/W1 thermostat terminals.	Ð	Ð	5
5.	Observe operation of furnace for next 25 minutes.	Ð	Ð	6
6.	Does fault occur again?	40	7	Ð
7.	Does a different fault occur?	8	9	Ð
8.	Go to page number indicated in Index for fault code flashed.	Ð	Ð	INDEX

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