Status Code 43
LOW-HEAT PRESSURE, DRAFT SAFEGUARD, OR AUXILIARY LIMIT SWITCH OPEN WHILE HIGH-HEAT PRESSURE SWITCH
IS CLOSED—THIS STATUS CODE CAN OCCUR AS A RESULT OF LOW-HEAT PRESSURE SWITCH LPS NOT MAKING,
DRAFT SAFEGUARD SWITCH DSS OPENING, AUXILIARY LIMIT SWITCH ALS1, 2 (IF USED) OPENING, OR HIGH-HEAT
PRESSURE SWITCH HPS IS MADE WHEN A CALL FOR HEAT IS INITIATED. REGARDLESS OF WHICH SWITCH OPENS,
2-STAGE FURNACE CONTROL OPERATES UNDER THE SCENARIOS SHOWN BELOW. KEEP IN MIND THAT WHENEVER
2-STAGE FURNACE CONTROL SHUTS UNIT DOWN, GAS REMAINS OFF OR SHUTS OFF IMMEDIATELY, AND IF INDUCER
IS RUNNING, IT CONTINUES RUNNING FOR 5 SEC.
•
CALL FOR HEAT—If high-heat pressure switch HPS is made when a call for heat is initiated, 2-stage furnace control flashes status code 43
until high-heat pressure switch HPS opens, then heating cycle begins.
•
LOW HEAT
1. PREPURGE—If low-heat pressure switch LPS does not make within 30 sec after a call for heat is initiated, 2-stage furnace control changes
inducer motor speed to high-heat speed. If high-heat pressure switch HPS makes and low-heat pressure switch LPS is still open, 2-stage
furnace control starts flashing status code 43. If low-heat pressure switch LPS eventually closes, 2-stage furnace control changes inducer
motor speed back to low-heat speed, stops flashing status code 43, and continues heating cycle. If low-heat pressure switch LPS fails to
close within 5 minutes, 2-stage furnace control continues flashing status code 43, shuts unit down, and waits 15 minutes before restarting
heating cycle.
2. AFTER IGNITION—If low-heat pressure switch LPS opens after burners ignite, 2-stage furnace control shuts unit down and flashes status
code 32 once. At the same time, 2-stage furnace control turns on blower or continues to operate blower at low-heat blower speed for a 90-sec
blower off delay period. When inducer shuts off if high-heat pressure switch is made, 2-stage furnace control stops flashing status code 32
and starts flashing status code 43. After 90-sec blower off delay period is completed, 2-stage furnace control stops flashing status code 43
and restarts heating cycle.
•
HIGH HEAT
1. PREPURGE—If high-heat pressure switch HPS makes and low-heat pressure switch LPS is still open, 2-stage furnace control starts flashing
status code 43. If low-heat pressure switch LPS eventually closes, 2-stage furnace control stops flashing status code 43 and continues heating
cycle. If low-heat pressure switch LPS fails to close within 5 minutes, 2-stage furnace control continues flashing status code 43, shuts unit
down, and waits 15 minutes before restarting heating cycle.
2. AFTER IGNITION—If low-heat pressure switch LPS opens after burners ignite, 2-stage furnace control starts flashing status code 43, shuts
unit down, turns blower on or changes blower speed to low-heat blower speed for a 90-sec blower off delay period, stops flashing status
code 43, and restarts heating cycle.
NOTE:
On furnaces with variable-speed ICM blower motors, blower turns on and operates at continuous fan speed if low-heat pressure switch
LPS opens during blower on delay period.
STEP
ACTION
YES
NO
GO TO
1.
Turn power off, remove blower door, and disconnect R thermostat lead from
furnace control board.
—
—
2
2.
Turn power on and depress door switch. Use a piece of tape to hold switch
closed.
—
—
3
3.
Jumper R and W/W1 thermostat terminals.
—
—
4
4.
Observe operation of furnace through 1 heating cycle.
—
—
5
5.
Does status code 43 flash?
9
6
—
6.
Does a different status code flash?
7
8
—
7.
Go to page number indicated in Index for section covering status code.
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—
INDEX
8.
Go to page number indicated in Index for CLEANUP AND START-UP IN-
STRUCTIONS.
—
—
INDEX
9.
Do you have 24 vac across BROWN wire on high-heat pressure switch HPS
and C
OM
-24V on 2-stage furnace control?
40
10
—
10.
Do you have 24 vac across connector terminal PL1-6 and C
OM
-24V on 2-stage
furnace control?
12
11
—
11.
Replace 2-stage furnace control.
—
—
8
12.
Do you have 24 vac across ORANGE wire on low-heat pressure switch LPS
and C
OM
-24V on 2-stage furnace control?
36
13
—
13.
Turn power off. Disconnect jumper wire across R and W/W1 thermostat termi-
nals.
—
—
14
14.
Do you have continuity across draft safeguard switch DSS?
NOTE: Answer YES to this question if installation has a Category III vent sys-
tem. Category III vent systems cause draft safeguard switch DSS to trip if in-
stalled.
CAUTION: Category I vent systems must have draft safeguard switch installed
in order to detect a blocked vent.
22
15
—
15.
Can draft safeguard switch DSS be reset?
17
16
—
16.
Replace draft safeguard switch DSS.
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—
8
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