Post Purge

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.

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.

340968-XIM-A-0108

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.

14	Johnson Controls Unitary Products

340968-XIM-A-0108 specifications

Johnson Controls 340968-XIM-A-0108 is a sophisticated component designed for advanced building management and automation systems. This device is engineered to enhance the performance and efficiency of HVAC (Heating, Ventilation, and Air Conditioning) systems, contributing significantly to energy conservation and optimal climate control in commercial and industrial environments.

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