STEP
ACTION
YES
NO
GO TO
47
Is inducer blower wheel okay?
49
48
48
If possible, replace inducer wheel. Otherwise replace in-
ducer motor assembly.
8
49
Is there any frost build-up on combustion-air inlet?
50
51
50
The problem is caused by reversed vent and combustion-air
pipes or some other moist air entering combustion-air pipe.
15
51
You have excessive restriction in combustion-air or vent
pipe.
15
52
Make sure all pins and wire leads are in tact on connectors
between variable speed furnace control and the inducer
motor.
53
53
Replace the inducer motor or the inducer motor assembly.
If problem still persists after replacing the inducer motor,
contact your distributor.
8
54
Turn power off and disconnect jumper from the R and
W/W1 thermostat terminals.
55
55
Turn power on and jumper the R, W/W1, and W2 thermo-
stat terminals.
56
56
Does fault occur a few seconds after the high heat pressure
switch HPS makes?
Note: Check for 24-vac between the N.O. (Normally Open)
contact on high heat pressure switch HPS and Com on the
variable speed furnace control to know when the high heat
pressure switch HPS makes.
57
8
57
Turn power off and disconnect jumper from the R, W/W1,
and W2 thermostat terminals.
58
58
Connect 1 side of slope manometer with a tee to collector
box pressure tap. Connect other side with a tee to gas
valve pressure fitting. Refer to pressure check diagram in
Appendix C.
59
59
Turn power on and jumper the R, W/W1, and W2 thermo-
stat terminals.
60
60
Do you have more than 1.9 in. wc pressure drop across
heat exchangers when high heat pressure switch HPS
makes?
Note: Check for 24-vac between the N.O. (Normally Open)
contact on high heat pressure switch HPS and Com on the
variable speed furnace control to know when the high heat
pressure switch HPS makes.
45
49
Status Code 43
LOW-HEAT PRESSURE SWITCH OPEN WHILE HIGH-HEAT PRESSURE SWITCH IS CLOSED -
This status code
can occur as a result of the low heat pressure switch LPS not making during a call for high heat. Keep in mind that whenever status code 43
occurs the variable speed furnace control shuts unit down, turns the inducer off, and gas remains off.
•
LOW HEAT PREPURGE - If the high heat pressure switch HPS makes and the low heat pressure switch LPS is still open the variable speed
furnace control starts flashing status code 43, shuts unit down, and waits 2 minutes before restarting the heating cycle.
•
HIGH HEAT PREPURGE - If the high heat pressure switch HPS makes and the low heat pressure switch LPS is still open the variable speed
furnace control starts flashing status code 43, shuts unit down, and waits 2 minutes before restarting the heating cycle.
STEP
ACTION
YES
NO
GO TO
1
Turn power off, remove the blower access panel and dis-
connect the R thermostat lead from the furnace control
board.
2
2
Turn the power on and depress the door switch. Use a
piece of tape to hold switch closed.
3
3
Jumper the R, W/W1, and W2 thermostat terminals.
4
4
Observe the operation of the furnace until ignition.
5
5
Does status code 43 flash?
9
6
6
Does a different status code flash?
7
8
7
Go to page number indicated in the Index for the section
covering the status code.
INDEX
8
Go to page number Indicated in Index for CLEANUP AND
START-UP INSTRUCTIONS.
INDEX
9
Are the pressure switches wired correctly?
11
10
10
Fix problem.
8
33
