129099-BUM-J-0112
8
Johnson Controls Unitary Products
FURNACE CONTROL DIAGNOSTICS
The furnace has built-in, self diagnostic capability. If a system problem
occurs, a fault code is shown by a blinking green LED. It is located
behind a clear view port in the blower compartment door. DO NOT turn
off furnace power as this action will clear the control's memory of the
fault.
The control continuously monitors its own operation and the operation
of the system. If a failure occurs, the LED will indicate the failure code. If
the failure is internal to the control, the light will stay on continuously. In
this case, the entire control should be replaced as the control is not field
repairable.
Flash sequence codes 1 through 6 are as follows: LED will turn “on” for
one second and “off” for one second. This pattern will be repeated the
number of times equal to the code. For example, six “on” flashes equals
a number 6 fault code.
All flash code sequences are broken by a 2 second “off” period.
1 FLASH: Ignition failure.
2 FLASH: Combustion air pressure switch closed, this indicates that the
normally open pressure switch contacts are stuck in the closed position.
The control confirms these contacts are open at the beginning of each
heat cycle. This would indicate a faulty pressure switch or mis-wiring.
3 FLASH:
Combustion air pressure switch failed to close, this indicates
the normally open pressure switch contact did not close at the begin-
ning of the heat cycle. This could be caused by a number of problems;
faulty inducer, blocked vent pipe, broken pressure switch hose or faulty
pressure switch.
4 FLASH:
Limit Switch Open, this indicates that a primary or auxiliary
limit switch has opened its normally closed contacts. With this fault code
the control will operate the supply air blower and inducer. This condition
may be caused by: dirty filter, improperly sized duct system, incorrect
blower speed setting, incorrect firing rate or faulty blower motor.
5 FLASH:
Gas flow with no call for heat. Check gas valve and gas valve
wiring.
RAPID FLASHES:
Reverse Polarity, reverse polarity indicates reverse
line voltage polarity. Both heating and cooling will be affected. Check
polarity of both.
STEADY ON: Normal Operation.
60 MINUTE AUTOMATIC RESET FROM LOCKOUT: This control
includes a "watchdog" type circuit that will reset from a lockout condition
after 60 minutes. Operational faults 1, 3, 4 and Steady On will be reset.
This provides protection to an unoccupied structure if a temporary con-
dition exists causing a furnace malfunction. An example would be a low
incoming gas supply pressure preventing unit operation. When the gas
pressure is restored, at some point the "watchdog" would restart the
unit and provide heat for the house.
NOTE:
If a flame is detected the control flashes the LED for 1/8 of a
second and then enters a flame stabilization period.
IGNITION CONTROL
Normal flame sense current is approximately
3.7 microamps DC (
a)
Low flame signal control lockout point is
0.9 microamps DC (
a)
FIGURE 7:
Furnace Event Control Schedule
Thermostat Calling for Heat
Thermostat Satisfied
(Seconds)
THERMOSTAT
INDUCER
IGNITOR
MAIN VALVE
CIRCULATING
BLOWER
OFF
OFF
OFF
OFF
OFF
ON
ON
ON
OFF
OFF
ON
OFF
OFF
OFF
OFF
OFF
15 Sec.
Post
Purge
Fan on Delay
12 Seconds
0
0
60, 90, 120, 180 SEC.
Selectable Fan Off Delay
5
32
