Bryant 355MAV Troubleshooting Manual page 22

STEP
11. You have an open wire or bad terminal on the YELLOW wire from the variable speed furnace
control to the low heat pressure switch LPS.
12. Repair or replace the main wire harness.
13. Replace the variable speed furnace control.
14. At start of cycle as inducer is ramping up, does low heat pressure switch LPS make then
break?
15. 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.
16. Fix problem.
17. Is 24-vac across ORANGE wire on the low heat pressure switch LPS and C
variable speed furnace control?
18. Is 24-vac across connector terminal PL1-4 and C
19. Turn power off and disconnect jumper wire across R and W/W1 thermostat terminals.
20. You have an open circuit between the low heat pressure switch LPS and the variable speed
furnace control. This includes all the ORANGE wire interconnecting the low heat pressure
switch LPS to the variable speed furnace control. It also includes the low gas pressure switch
LGPS (if used).
Check the continuity across the low gas pressure switch LGPS (if used). If there is no
continuity check the propane line pressure. If the propane line pressure is correct replace the
low gas pressure switch LGPS.
Check the continuity of each ORANGE wire interconnecting the low heat pressure switch LPS
and the variable speed furnace control. Repair open wire or replace harness.
21. Turn power off and disconnect jumper wire across R and W/W1 thermostat terminals.
22. 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.
23. Turn power on and jumper R and W/W1 thermostat terminals.
24. Do you have atleast 0.95 in. wc pressure drop (0.75 in. wc on 040 model) across heat
exchangers when fault occurs?
25. Replace the pressure switch assembly.
26. Is inducer motor rotating in direction indicated on the inducer housing?
27. Replace inducer motor or inducer motor assembly.
28. Turn power off.
29. Is inducer wheel okay?
30. If possible, replace inducer wheel. Otherwise, replace inducer motor assembly.
31. Is the inducer wheel properly mounted to the inducer motor shaft?
32. Is there any frost build-up on the combustion-air inlet?
33. The problem is caused by reversed vent and combustion-air pipes or some other moist air
entering combustion-air pipe.
34. You have excessive restriction in combustion-air or vent pipe. Also check for proper vent
sizing for installation.
35. Continue to observe furnace operation for 20 minutes or until status code starts flashing.
36. Does status code 32 flash?
37. Does a different status code flash?
38. Turn power off and disconnect jumper wire across R and W/W1 thermostat terminals.
39. 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.
40. Turn power on and jumper R and W/W1 thermostat terminals.
41. Monitor slope manometer. Does the pressure reading appear to be stable when fault occurs?
42. Check for a sag in vent pipe or partially clogged drain trap or line. Also check for improperly
plumbed drainage tubing within furnace. Install combustion air disk if not used or add
additional restriction to combustion-air inlet.
43. Does the pressure reading slowly drop off before flashing status code 42?
44. Replace pressure switch assembly. If problem persists, check wiring for an intermittent
connection in low heat pressure switch LPS circuit.
45. Check for partially clogged drain trap or line. 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.
ACTION
-24V on variable speed furnace control?
OM
- 22 -
YES
15
-24V on 18
OM
13
25
28
31
32
33
38
7
43
45
NO GO TO
12
8
8
17
16
8
21
19
20
8
22
23
24
26
8
27
8
29
30
8
16
34
16
16
36
37
8
39
40
41
42
8
44
8
8