48/50PG and PM
Space Sensor Control
Space sensor staging control is an adaptive anticipation control that weighs the actual space demand against the trend of that demand. It also honors stage time guards and supply air limits. The demand for heating in the space is displayed as the Heating Demand (Run Status→HEAT→DMD.H). The control tries to anticipate the change in the space because of its current stage status. This anticipation is based on the Heat Demand Trend (Operating Modes →HEAT→TRD.H). This trend will show the control how the space is reacting to the current running conditions and help it decide when to add or remove one stage from the requested stages. The Heat Stage Increase Time (Configuration→HEAT→H.INC) or the Heat Stage Decrease Time (Configuration→HEAT →H.DEC) has to expire before another stage can be added or a stage can be subtracted. If at any time the Supply−Air Temperature (SAT) rises above the Maximum Supply Air Temperature Lower Level (Configuration→HEAT→SAT→SAM.L), the requested stages will not be allowed to increase. If at any time the SAT rises above the Maximum Supply Air Temperature Upper Level (Configuration→HEAT→SAT→SAM.U), the requested stages will be reduced by one without honoring H.DEC.
Heat Relay Control
The heat relay control is responsible for energizing or de−energizing the MBB’s heat stage relays and works hand in hand with the staging control. As the staging control requests stages, the heat relay control determines what actual heat relays are available or energized and tries to provide stages for what is requested. The availability of a heat relays depends on heat being installed, how many stages, and time guards. The type of Heat Installed (Configuration→HEAT→HT.TY) must be set for gas or electric for any stages to be available. The Number of Heat Stages (Configuration→HEAT→N.HTR) configuration tells the control how many heat relays can be used. Heat Stage 1Timeguard (Run Status→HEAT→TG.H1) and Heat Stage 2 Timeguard (Run Status→HEAT→TG.H2) display the time a respective heat relay has before it is available for use. The available stages at any given time are displayed as Available Heating Stages (Run Status →HEAT→AVL.H). The actual heat relays on at any given time are displayed as Actual Heating Stages (Operating Modes→HEAT →ACT.H). Heat Stage 1 Relay (Run Status→HEAT→HT.1) and Heat Stage 2 Relay (Run Status→HEAT→HT.2) are displayed on when the respective relay is energized. There are time guards to protect from short cycling, Heat Minimum On Time (Configuration→HEAT→MRT.H) and Heat Minimum Off Time (Configuration→HEAT→MOT.H) apply before a heat relay can be turned back on or turned off.
Integrated Gas Controller (IGC)
The heat staging is determined as described above and the Integrated Gas Controller (IGC) initiates the gas heat module start−up. The Integrated Gas Controller (IGC) minimum on−time of 1 minute will be followed even if Heat Minimum On Time (Configuration→HEAT→MRT.H) is lower and during Service Test. If the IGC temperature limit switch opens within 10 minutes of the end of the gas heat cycle, the next fan off delay will be extended by 15 seconds. The maximum delay is 3 minutes. Once modified by the IGC, the fan off delay will not change back to the configured Fan−off Delay, Gas Heat (Configuration→HEAT →FOD.G) unless power is reset to the control. A light emitting diode (LED) is provided on the IGC to indicate status. During normal operation the LED is continuously on. See the Troubleshooting section if the LED is off or flashing. The IGC is located behind the gas section access panel door.
When the control energizes Heat Stage 1 Relay (Run Status →HEAT→HT.1), power is sent to the W terminal on the IGC board. A check is made to ensure that the rollout switch and limit switch are closed. The induced−draft motor is then energized, and when speed is proven with the Hall Effect sensor on the motor, the ignition activation period begins. The burners will ignite within 5 seconds. If the burners do not light, there is a 22−second delay before another 5−second attempt. If the burners still do not light, this sequence is repeated for 15 minutes. After the 15 minutes have elapsed, if the burners still have not lit, heating is locked out. The control will reset when the request for heat is temporarily removed. When ignition occurs, the IGC board will continue to monitor the condition of the rollout switch, limit switches, the Hall Effect sensor, as well as the flame sensor. If the unit is controlled through a room thermostat or space sensor set for fan auto, 45 seconds after ignition occurs the indoor−fan motor will be energized (and the outdoor−air dampers will open to their minimum position). If for some reason the over temperature limit opens prior to the start of the indoor fan blower, on the next attempt, the 45−second delay will be shortened to 5 seconds less than the time from initiation of heat to when the limit tripped. Gas will not be interrupted to the burners and heating will continue. Once modified, the fan on delay will not change back to 45 seconds unless power is reset to the control. When the control energizes Heat Stage 2 Relay (Run Status→HEAT→HT.2), power is supplied to the second stage of the main gas valve. If both stage 1 and stage 2 of the gas valve close, gas will be turned off to the main burners.
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