282911-YIM-B-0807
14
Unitary Products Group
The control recognizes a call for 2nd stage heat when W2 is
energized (connected to "R"). The control energizes the high
gas output and induced draft motor on high speed.
If the call for 2nd stage heat goes away and the 1st stage call
remains, the control de energizes the high gas valve, drops
inducer speed to low, and returns to low heat operation.
Response to loss of W1, low pressure switch, and flame are
identical to low heat operation.
POST PURGE
The control board runs the induced draft motor for a 30 sec-
ond post-purge period, and then de-energizes the inducer. If
a call for heat occurs during post-purge, the control finishes
the post-purge, drops inducer out to re-prove open pressure
switch before continuing with the heat cycle.
HEAT BLOWER OFF DELAY
The control board de-energizes the indoor blower motor after
a delay time as selected by movable shunt (60, 90, 120 or
180 seconds). Blower timing begins when the thermostat is
satisfied or heat cycle was interrupted. The control returns to
standby when the blower off delay is complete.
If the thermostat call for heat returns before the blower off
delay is complete, the control begins an ignition sequence
with pre-purge while the blower off delay continues.
LOCKOUT
While in lockout, the control board keeps the pilot gas valve,
main gas valve and induced draft motor de-energized.
Lockouts due to failed ignition or flame losses may be reset
by removing the call for heat (W1) for more than 1 second,
but less than 20 seconds, or by removing power from the
control for over 0.25 seconds. The control will automatically
reset lockout after 60 minutes.
Lockouts due to detected internal control faults will reset after
60 minutes or power interruption.
HIGH TEMPERATURE LIMIT SWITCH
Any time the high temperature limit switch is open the control
board will run the indoor blower motor on heat speed, the
inducer (on high speed for 2 stage models), de-energize the
gas valve, and flash "6" on the LED. When the high tempera-
ture switch closes, the control will restart the ignition
sequence beginning with pre-purge.
ROLLOUT SWITCH
If the rollout switch opens for more than 0.25 seconds, the
control board will run the inducer (on high speed for 2 stage
models) for a post-purge period, immediately de-energize the
gas valve, and flash "7" on the LED. The blower output will be
energized during an open rollout condition.
If the rollout switch closes, the control shall remain locked out
until power removed or "W" is removed.
Rollout switch lockout shall not reset automatically.
POWER INTERRUPTIONS
Power interruptions of any duration shall not cause lockout or
any operation requiring manual intervention.
FLAME PRESENT WITH GAS OFF
If flame is sensed for longer than 4.0 seconds during a period
when the gas valve should be closed, the control will enter
lockout flashing "8" on the LED. The control will turn on the
inducer blower while the flame is present.
GAS VALVE STUCK OPEN OR CLOSED
If either or both Pilot and Main Gas valve outputs are sensed
to be off for more than 1 second when commanded to be on,
the control board shuts off all outputs and enters a hard
lockout flashing "9" on the LED.
If the Pilot valve or Main valve output is sensed to be
energized for more than 1 second when commanded to be
off, the control de-energizes the induced draft motor (if flame
is not present) to attempt to open the pressure switch to de-
energize the gas valve. If the pilot or main gas valve is still
sensed as energized after the inducer has been off for 5
seconds, the control re-energizes the inducer to attempt to
vent the unburned gas. In either case, the control enters a
hard lockout flashing "9" on the LED. If the pilot or main valve
becomes Un-Welded the inducer will de-energize, but the
control will remain in a hard lockout and not respond to any
thermostat demands.
The only way to recover from a hard lockout is to remove and
then reapply 24VAC power to the control board.
FLAME SENSE CIRCUIT FAILURE
If the control detects an internal hardware failure in the flame
sense circuit, it shuts off all outputs and enters a hard lockout
flashing "10" on the LED. The control will not respond to
thermostat demands during a hard lockout.
The only way to recover from a hard lockout is to remove and
then reapply 24VAC power to the control. If problem persist
after removal and reapplication of 24VAC power, the board
may need to be replaced.
SAFETY CONTROLS
The control circuit includes the following safety controls:
1.
Limit Switch (LS)
- This control is located inside the
heat exchanger compartment and is set to open at the
temperature indicated in the Temperature Controls Table
of the unit wiring diagram. It resets automatically. The
limit switch operates when a high temperature condition
caused by inadequate supply air flow occurs, thus shut-
ting down the ignition control and closing the main gas
valve and energizing the blower.
