Bryant 355MAV Troubleshooting Manual page 30

Do you have more than 1.9 in. wc pressure drop across heat exchangers when high-pressure
switch HPS makes?
66.
NOTE: Check for 24v between the N.O. (Normally Open) contact on high-pressure switch
HPS and Com on furnace control board to know when high-pressure switch HPS makes.
→67.
Does fault occur a few sec after main burners ignite?
→68.
Observe operation of furnace in high heat for next 8 minutes or until fault occurs.
→69.
Does the fault occur?
→70.
If problem still persists check for internal restriction in coupling box or secondary heat exchangers.
Fault Code 43
PRESSURE SWITCH CALIBRATION FAULT—INDICATES LOW-PRESSURE SWITCH LPS AND HIGH-PRESSURE SWITCH
HPS "MAKE" POINTS DURING HIGH-HEAT PURGE ARE NOT WITHIN CALIBRATION RANGE. THIS IS DETERMINED BY
READING INDUCER MOTOR RPM WHEN LOW-PRESSURE SWITCH LPS AND HIGH-PRESSURE SWITCH HPS MAKE. THEN
THE FOLLOWING COMPARISON IS MADE:
IF THIS RELATIONSHIP IS NOT WITHIN RANGE SPECIFIED, FURNACE CONTROL BOARD STARTS FLASHING FAULT
COLDE 43, SHUTS UNIT DOWN (INDUCER RUNS FOR 15 SEC), WAITS 2 MINUTES, STOPS FLASHING FAULT CODE, AND
RESTARTS HEATING CYCLE.
→
IT CAN ALSO INDICATE THAT THE HIGH-PRESSURE SWITCH HPS MADE BEFORE THE LOW-PRESSURE SWITCH LPS
DURING EITHER LOW-HEAT OR HIGH-HEAT PURGE.
STEP
Turn power off, remove blower access panel, and disconnect all thermostat leads from furnace con-
1.
trol 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 on furnace control board.
4. Observe operation of furnace for several minutes or until fault occurs.
5. Does fault occur again?
6. Does a different fault occur?
7. Go to page number indicated in Index for fault code flashed.
Go to page number indicated in Index for CLEANUP AND START-UP
8.
INSTRUCTIONS.
9. Is collector box and inducer housing properly draining condensate?
10. Fix problem.
11. Are pressure switches wired correctly?
12. Replace pressure switch assembly.
Do you have 24v between C (Common) on low-pressure switch LPS and Com on furnace control
13.
board?
The YELLOW wire to low-pressure switch LPS is not making good connection. Repair wire or re-
14.
place harness.
Turn power off and disconnect jumper wire across R, W/W1, and W2 thermostat terminals. Turn
15. power on and wait a few sec for self test, then reconnect jumper across R, W/W1, and W2 thermo-
stat terminals.
Do you have 24v between connector terminal PL2-2 and Com on furnace control board when fault
16.
occurs?
17. Replace furnace control board.
18. Turn power off.
Do you have continuity across terminal PL2-2 and N.O. (Normally Open) contact on low-pressure
19.
switch LPS?
The ORANGE wire from low-pressure switch LPS to furnace control board is not making good con-
→20.
nection or low gas pressure switch LGPS (when used) is open. Check propane line pressure if us-
ing LGPS otherwise repair wire or replace harness.
Turn power off and disconnect jumper wire across R, W/W1, and W2 thermostat terminals. Discon-
21. nect BROWN wire from N.O. (Normally Open) contact on high-pressure switch HPS. Turn power on
and wait a few sec for self test, then reconnect jumper across R and W/W1 thermostat terminals.
22. Does a Fault Code 32 occur?
23. Reconnect BROWN wire to N.O. (Normally Open) contact on high-pressure switch HPS.
RPM (low)
‹ ‹
0.55 0.90
RPM (high)
ACTION
—30—
47 44 —
63 68 —
— — 69
22 59 —
— — 14
YES NO GO TO
— — 2
— — 3
— — 4
— — 5
9 6 —
7 8 —
— — INDEX
— — INDEX
11 25 —
— — 8
13 10 —
— — 8
15 14 —
— — 8
— — 16
21 18 —
— — 8
— — 19
12 20 —
— — 10
— — 22
17 23 —
— — 24