Lennox International Inc LZP-2 Sequence of Operation, Heating And Cooling Equipment Operation

Sequence of Operation

A Time Delay Override (TDO) button is available on the control panel to speed up the internal timer by a factor of 60 for system checkout. One second of holding down the button relates to one minute of speed up time in the control.

HEATING AND COOLING EQUIPMENT OPERATION

Heating Operation

When a zone makes a call for Heat, the W output terminal will energize. The G terminal will also energize if the ELECTRIC/GAS jumper is in the ELECT position. The W terminal de-energizes when (1) all zones stop calling for Heat, (2) the call has exceeded the heat/cool changeover time limit while a cooling call exists or (3) the call is interrupted by the high limit setting. When the W terminal is de-energized, a minimum off time delay of 4 minutes must elapse before it can be energized again.

Fan Purge Time Delay

If the ELECTRIC/GAS jumper is in the ELECT position and the PURGE/NO PURGE jumper is in the PURGE position, the G terminal will remain energized for one minute after the W terminal is de-energized. The NO PURGE setting is the preferred purge control setting for Lennox equipment. Lennox equipment includes controls which sequence the indoor fan off after a call for heat has been satisfied.

If the ELECTRIC/GAS jumper is set in the GAS position, the G terminal does not turn on during purge regardless of the position of the PURGE or NO PURGE switch. Lennox furnaces will control the purge though the furnace control board cool down feature. The cool down time is often adjustable at the furnace control board up to 3.5 minutes. NO PURGE is the preferred method of purge when this zone panel is applied to Lennox equipment.

Cooling Operation

When a zone makes a call for Cooling, the Y and G terminals will energize. The Y terminal de-energizes when (1) all zones stop calling for Cooling, (2) the call has exceeded the heat/cool changeover time limit while a heat call exists or (3) the call is interrupted by the low limit temperature setting. When the Y terminal is de- energized, a minimum off time delay of 4 minutes must elapse before it can be energized again.

Fan Purge Time Delay

If the PURGE/NO PURGE jumper is in the PURGE position, the G terminal will remain energized for one minute after the Y terminal is de-energized. If the jumper is in the NO PURGE position, the G terminal will de-energize immediately.

Heat/Cool Changeover: When a call for heating or cooling exists and an opposing call is made from another zone, a 20 minute timer is activated. If the original call is not satisfied within that 20-minute time period, the call will be interrupted, turning the equipment off and allowing for the normal fan purge cycle and minimum equipment off time. The opposing call will then be answered. After 20 minutes, if the original call still exists, the opposing call will be interrupted and the original call can once again be recognized.

High/Low Limit Temperature: The high/low limit temperature settings are designed to prevent the heat exchanger from overheating or the cooling coil from freezing. The temperature sensor in the supply duct senses the discharge air temperature and interrupts the heating/cooling equipment (depending on the Heat and Cool temperatures set on the control panel) before overheating/freezing occurs. When a heating/cooling call is interrupted by the high/low temperature limit, the zone control panel turns the equipment off and energizes the G terminal (if not already energized). The W or Y LED on the control panel will flash during a high/low limit temperature interrupt. Once the temperature drops/rises 10°F and the minimum off time has expired, the equipment is turned back on if the call for conditioning still exists. The Heating/Cooling LED will stop flashing.

IMPORTANT: Should a short or open circuit be detected across the DAS terminals, the zone system will respond only to Zone 1 and the dampers will not energize.

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