Bryant 355MAV Troubleshooting Manual page 20

- HIGH HEAT
1. PREPURGE - If the high heat pressure switch HPS does not make within 45 seconds after the low-heat pressure switch LPS made the
variable speed begins flashing status code 31, shuts unit down, waits 2 minutes, stops flashing status code 31, and restarts heating cycle.
If high heat pressure switch HPS opens before ignition, the variable speed starts flashing status code 31 and ramps inducer RPM up until the
high heat pressure switch HPS remakes. When the high heat pressure switch HPS remakes the variable speed stops flashing status code 31
and continues heating cycle. If high heat pressure switch HPS does not remake within 45 sec after opening, the variable speed continues
flashing status code 31, shuts unit down, waits 2 minutes, stops flashing status code 31, and restarts heating cycle.
2. LOW HEAT TO HIGH HEAT TRANSITION - If the high heat pressure switch HPS fails to make within 45 seconds after high heat was
requested the variable speed furnace control shuts unit down and begins flashing status code 31. After the blower off-delay is completed the
variable speed will stop displaying status code 31 and if there is a call for heat, begin a new heating cycle. This new heating cycle will be
restricted to high heat.
3. STEADY-STATE - If the high heat pressure switch HPS opens the variable speed starts flashing status code 31 and ramps inducer RPM up
until the high heat pressure switch HPS remakes. When the high heat pressure switch HPS remakes the variable speed stops flashing status
code 31 and continues heating cycle. If high heat pressure switch HPS does not remake within 45 sec after opening, the variable speed shuts
the unit down and continues flashing status code 31. After the blower off-delay is completed the variable speed will stop displaying status
code 31 and if there is a call for heat, begin a new heating cycle. This new heating cycle will be restricted to high heat.
4. HIGH HEAT TO LOW HEAT TRANSITION – When using a 2-stage thermostat and W2 is de-energized, the high heat pressure switch
HPS must open within 5 seconds. If the high heat pressure switch HPS does not open within 5 seconds after W2 is de-energized, the variable
speed switches back to high heat and starts flashing status code 31. After the call for heat is satisfied and the blower off-delay is completed
the variable speed will stop displaying status code 31.
STEP
1. Turn power off, remove 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 power on and depress door switch. Use a piece of tape to hold switch closed.
3. Jumper R, W/W1, and W2 thermostat terminals.
4. Wait 90 seconds before proceeding to the next step.
5. Does status code 31 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. Is 24-vac across GRAY wire on the high heat pressure switch HPS and C
speed furnace control?
10. Is 24-vac across connector terminal PL1-12 and C
11. You have an open wire or bad terminal on the GRAY wire from the variable speed furnace
control to the high heat pressure switch HPS.
12. Repair or replace the main wire harness.
13. Replace the variable speed furnace control.
14. The problem is caused by reversed vent and combustion-air pipes or some other moist air
entering combustion-air pipe.
15. Does the high heat pressure switch HPS make, then break several times at start of cycle before
faulting out?
16. The problem is either a sag in vent pipe or a clogged drain trap or line. Also check for
improperly plumbed drainage tubing within furnace.
17. Is 24-vac across BROWN wire on the high heat pressure switch HPS and C
variable speed furnace control?
18. Is 24-vac across connector terminal PL1-3 and C
19. You have an open wire or bad terminal on the BROWN wire from the high heat pressure
switch HPS to the variable speed furnace control.
20. Turn power off and disconnect jumper wire across R, W/W1, and W2 thermostat terminals.
21. 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.
22. Turn power on and jumper R, W/W1, and W2 thermostat terminals.
23. Do you have atleast 1.90 in. wc pressure drop across heat exchangers when status code 31
flashes?
24. Replace the pressure switch assembly.
25. Is inducer motor rotating in direction indicated on inducer housing?
26. Replace inducer motor or inducer motor assembly.
27. Turn power off.
ACTION
-24V on variable speed furnace control?
OM
-24V on variable speed furnace control?
OM
- 20 -
YES
9
7
-24V on variable 15
OM
11
16
-24V on 18
OM
13
24
27
NO GO TO
2
3
4
5
6
34
INDEX
INDEX
10
13
12
8
8
32
17
32
20
19
12
21
22
23
25
8
26
8
28