Status Code 43 - Low-Heat Pressure Switch Open While High-Heat Pressure Switch Is Closed - Bryant 355MAV Troubleshooting Manual

STEP
47. Is inducer blower wheel okay?
48. If possible, replace inducer wheel. Otherwise replace inducer motor assembly.
49. Is there any frost build-up on combustion-air inlet?
50. The problem is caused by reversed vent and combustion-air pipes or some other moist air
entering combustion-air pipe.
51. You have excessive restriction in combustion-air or vent pipe.
52. Make sure all pins and wire leads are in tact on connectors between variable speed furnace
control and the inducer motor.
53. Replace the inducer motor or the inducer motor assembly. If problem still persists after
replacing the inducer motor, contact your distributor.
54. Turn power off and disconnect jumper from the R and W/W1 thermostat terminals.
55. Turn power on and jumper the R, W/W1, and W2 thermostat terminals.
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. Turn power off and disconnect jumper from the R, W/W1, and W2 thermostat terminals.
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. Turn power on and jumper the R, W/W1, and W2 thermostat terminals.
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.
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
1. 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
2. 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
1. Shut the power off, remove the blower access panel and disconnect User Interface ABCD
connector (if used) or the R thermostat lead (if used) from the furnace control board.
2. Turn the power on and depress the door switch. Use a piece of tape to hold switch closed.
3. Jumper the R, W/W1, and W2 thermostat terminals.
4. Observe the operation of the furnace until ignition.
5. Does status code 43 flash?
6. Does a different status code flash?
7. Go to page number indicated in the Index for the section covering the status code.
8. Go to page number Indicated in Index for CLEANUP AND START-UP INSTRUCTIONS.
9. Are the pressure switches wired correctly?
10. Fix problem.
11. Is 24-vac across YELLOW wire to the low heat pressure switch LPS and C
variable speed furnace control?
12. Is 24-vac across connector terminal PL1-2 and C
13. 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. Repair it or replace the harness.
ACTION
ACTION
-24V on variable speed furnace control?
OM
- 30 -
YES
49
50
57
45
YES
9
7
11
-24V on 14
OM
13
NO GO TO
48
8
51
15
15
53
8
55
56
8
58
59
60
49
NO GO TO
2
3
4
5
6
8
INDEX
INDEX
10
8
12
18
8