Status Code 43 - Low-Heat Pressure Switch Open While Medium-Heat Pressure Switch Is Closed; Status Code 45 - Control Circuitry Lockout - Bryant 355CAV A Series Troubleshooting Manual

Status Code 43
LOW-HEAT PRESSURE SWITCH OPEN WHILE MEDIUM-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 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, MEDIUM, OR HIGH HEAT
1. PREPURGE - If the medium heat pressure switch MPS 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. Turn 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 and W/W1 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.
14. Is 24-vac across ORANGE wire on the low heat pressure switch LPS and C
variable speed furnace control?
15. Is 24-vac across connector terminal PL1-4 and C
16. Turn power off and disconnect jumper wire across R and W/W1 thermostat terminals.
17. You have an open circuit between the low heat pressure switch LPS and the variable speed
furnace control. This includes all the ORANGE wires 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.
18. Replace the variable speed furnace control.
19. Replace the pressure switch assembly.
Status Code 45
CONTROL CIRCUITRY LOCKOUT – Auto-reset after 1 hour due to:
1. Flame sense circuitry failure.
2. Software check error.
3. Gas valve relay stuck open.
Reset power to clear lockout. If status code re-occurs when power is re-applied replace variable speed furnace control.
ACTION
-24V on variable speed furnace control?
OM
-24V on variable speed furnace control?
OM
- 34 -
YES
9
7
11
-24V on 14
OM
13
-24V on 15
OM
18
NO GO TO
2
3
4
5
6
8
INDEX
INDEX
10
8
12
18
8
19
16
17
8
8
8