- 26 -
STEP
ACTION
YES
NO
GO TO
15.
Did the medium pressure switch MPS make, then break several times at start of cycle before
faulting out?
16
17
16.
The problem is either a sag in vent pipe or a clogged drain trap or line. Also check for
improperly plumbed drain tubing within furnace.
32
17.
Is 24-vac across VIOLET wire on the medium pressure switch MPS and C
OM
-24V on
modulating furnace control?
Note:
You may need to wait a few minutes for the modulating furnace control to ramp the
inducer motor back up to speed.
18
20
18.
Is 24-vac across connector terminal PL1-3 and C
OM
-24V on modulating furnace control?
13
19
19.
You have an open wire or bad terminal on the VIOLET wire from the medium pressure
switch MPS to the modulating furnace control.
12
20.
Turn power off and disconnect jumper wire across R and W/W1 thermostat terminals.
21
21.
Connect 1 side of slope manometer with a tee to collector box pressure tap. Refer to pressure
check diagram in Appendix C.
22
22.
Turn power on and jumper R and W/W1 thermostat terminals.
23
23.
Do you have at least 1.08 in. wc pressure drop across heat exchangers when status code 9
flashes?
24
25
24.
Replace the pressure switch assembly.
8
25.
Is inducer motor rotating in direction indicated on inducer housing?
27
26
26.
Replace inducer control (if you have 2 piece design) or inducer motor assembly.
8
27.
Turn power off.
28
28.
Is inducer wheel okay?
30
29
29.
Replace inducer motor assembly.
8
30.
Is the inducer wheel properly mounted to the inducer motor shaft?
33
32
31.
Were there any leaks or blockages found in steps 60-63?
32
14
32.
Fix problem.
8
33.
Does the inducer wheel turn freely?
60
32
34.
Continue to observe furnace operation for 20 minutes or until status code starts flashing.
35
35.
Does status code 9 flash?
37
36
36.
Does a different status code flash?
7
43
37.
Turn power off and disconnect jumper wire across R and W/W1 thermostat terminals.
38
38.
Connect 1 side of slope manometer with a tee to collector box pressure tap. Refer to pressure
check diagram in Appendix C.
39
39.
Turn power on and jumper R and W/W1 thermostat terminals.
40
40.
Monitor slope manometer. Does the pressure reading appear to be stable when fault occurs?
41
42
41.
Did the pressure gradually drop over time until the fault occurred?
If the pressure remained constant and then the fault all of sudden occurred go to step 50.
51
50
42.
Check for a sag in vent pipe or partially clogged drain trap or line. Also check for improperly
plumbed drain tubing within furnace.
8
43.
Turn power off and disconnect jumper wire across R and W/W1 thermostat terminals.
44
44.
Install the control door.
45
45.
Turn power on and jumper R and W/W1 thermostat terminals. Wait 1 minute.
46
46.
Does status code 9 flash?
48
47
47.
Does a different status code flash?
7
53
48.
Is there any frost build-up on the combustion-air inlet?
49
52
49.
The problem is caused by reversed vent and combustion-air pipes or some other moist air
entering combustion-air pipe.
32
50.
Replace pressure switch assembly. If problem persists, check wiring for an intermittent
connection in medium pressure switch MPS circuit.
8
51.
Check for partially clogged drain trap or line. Also check for improperly plumbed drainage
tubing within furnace. If furnace is installed in the horizontal position make sure the furnace
is pitched forward ¼ inch minimum to ½ inch maximum. If furnace is installed in the upflow
or downflow position make sure the furnace is level or pitched forward within ½ inch.
8
52.
You have excessive restriction in combustion-air or vent pipe. Also check for proper vent
sizing for installation.
32
53.
Put setup switch SW1-2 into the ON position.
54
54.
Put setup switch SW4-2 into the OFF position.
55
55.
Is status code 9 flashing?
57
56
56.
Does a different status code flash?
7
8
57.
Turn power off and disconnect PL1 from modulating furnace control.
58
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