York R-410A dimensions Heating Sequence Of Operation

279550-YIM-A-0207

The “Heat” Jumper on the CFM selection board should be set to “A”.

Fan Only CFM:

When the connection is made from “R” to “G”, the fan only mode is activated. In this mode, the blower will deliver 75% of the cooling system CFM. This connection is factory set from the manufacturer, but can be field adjusted.

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Figure 14: Control Board Speed Tap Location

Table 17: Delay Profile

Delay Tap	Regional Climate Type
Jumper at “A”	Standard Setting
Jumper at “B”	Humid Climate
Jumper at “C”	Dry Climate
Jumper at “D”	Temperate Climate

Operation

The unit is controlled by a conventional heating/cooling thermostat common to this class of equipment.

Heating Sequence Of Operation

Heat

The control board begins a call for heat when W1 is energized (connected to R). The control ignores W2 until pilot ignition has been established.

The control checks to see if the pressure switch is open. If the pressure switch is closed, the control board flashes “3” on the LED and waits indefinitely for it to open. When the pressure switch is sensed as open, the control begins pressure switch proving period. If the call for heat is lost, the control goes back to Standby.

Pressure Switch Proving

The control board energizes the induced draft motor (High speed for 2 stage model) and waits for the low pressure switch

to close. When the low pressure switch closes, the control begins Pre-purge period. If the call for heat is lost, the control de-energizes the inducer without post-purge and returns to standby.

If the low pressure switch does not close within 10 seconds of inducer energizing, the control board flashes “2” on the LED. If the pressure switch does not close within 5 minutes of inducer energizing, the control shuts off the inducer for 30 seconds, then energizes the inducer for another 5 minute try to close the pressure switch. This cycle continues indefinitely until either the pressure switch is proved closed, or the call for heat ends.

Pre-purge

The control board monitors the low pressure switch and ensures it remains closed during pre-purge. If the pressure switch opens, the control goes back to pressure switch proving mode. The control waits for a 15 second pre-purge period, then begins the ignition trial

Ignition Trial Period

The control board energizes the pilot gas valve and spark outputs for an 85 second Ignition trial. The control de-energizes the spark when flame is sensed and enters a flame stabilization period.

If flame is not established within the ignition trial period, the control de-energizes the spark and gas valve and begins an inter-purge period before attempting another ignition trial.

If the call for heat is lost during an ignition trial period, the control immediately de-energizes spark and gas. The control runs the inducer motor through a post purge period before de- energizing.

If the pressure switch is lost during an ignition trial period, the control immediately de-energizes spark and gas. The control begins pressure switch proving before an inter-purge and re- ignition attempt.

Pilot Flame Stabilization Period

The control board de-energizes the spark output, and waits for a 2 second flame stabilization period before energizing the main gas valve.

If flame is lost during the flame stabilization period, the control board counts it as a flame loss and retries ignition or locks out flashing a “5” on the LED.

Heat Blower On Delay

The control board waits for 30 seconds and then energizes the indoor blower heat speed. Blower on delay time begins at the start of flame proving period in the trial for ignition.

If the thermostat demand for heat is removed, the control de- energizes the gas valve, energizes the blower on heat speed and initiates a post-purge and heat blower off delay.

22 Unitary Products Group