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. See Figure 8 or 9 for location.
The 48/50PD unit control will switch automatically between cooling and heating to maintain space temperature. To minimize unnecessary changes there is a 10 minute Mode Select Timeguard (Operating Modes→HEAT→MS.TG) after the last stage of cooling turns off and before the heating is allowed.
The unit tries to maintain the space temperature at the Occupied Heat Setpoint (Setpoint→OHSP) or the Unoccupied Heat Setpoint (Setpoint→UHSP). See the Occupancy Determination section for factors that affect the Currently Occupied (Run Status→VIEW→OCC) parameter. Heating Demand (Operating Modes→HEAT→SPT→DMD.H) is equal to the occupied or unoccupied set point minus the Space Temperature (Operating Modes→HEAT→SPT→SPT) [DMD.H = Setpoint - SPT].
Two methods are used to add and remove stages of heating for 48PD units. The first method causes the unit to operate around its steady state number of stages. For example, if the correct number of stages is between 0 and 1, this method will cause the first stage to cycle. If the correct number of stages is between 1 and 2, this method will cause the second stage to cycle. The second method causes the unit to find the steady-state number of stages. Details of these methods are provided below.
The control uses two methods to add a stage of heating. The first method will add a stage of heating when the Heating Demand (Operating Modes→HEAT→SPT→DMD.H) plus the change in Spacetemp Trend (Operating Modes→HEAT→SPT→TRND) times the Heat Thermal Lag Factor (Operating Modes→HEAT→SPT→H.LAG) is greater than the SPT Heat Demand (+) Level (Operating Modes→HEAT→SPT→HT.PD) [DMD.H + change TRND * H.LAG > HT.PD].
The second method will add a stage of heating when Heat Demand (Operating Modes→HEAT→SPT→DMD.H) is greater that the
SPT Heat Demand (+) Level (Operating Modes→HEAT→SPT→HT.PD) plus 0.5 degrees F [DMD.H > HT.PD + 0.5] and the heat demand is changing at a rate greater than 0.3 degrees F per minute.
The control uses two methods to remove a stage of heating. The first method will remove a stage of heating when the Heating Demand (Operating Modes→HEAT→SPT→DMD.H) plus the
change in Spacetemp Trend (Operating Modes→HEAT→SPT→TRND) times the Heat Thermal Lag Factor (Operating Modes→HEAT→SPT→H.LAG) is less than the SPT Heat Demand (-) Level (Operating Modes→HEAT→SPT→HT.ND) [DMD.H + change TRND * H.LAG < HT.ND].
The second method will remove a stage of heating when Heat Demand (Operating Modes→HEAT→SPT→DMD.H) is less that the SPT Heat Demand (-) Level (Operating Modes→HEAT→SPT→HT.ND) minus 0.5 degrees F [DMD.H < HT.PD - 0.5] and the heat demand is changing at a rate greater than 0.3 degrees F per minute.
Configurable delays also apply when adding stages per Heat Stage Increase Time (Configuration→HEAT→H.INC) or removing
stages per Heat Stage Decrease Time (Configuration→HEAT→H.DEC). Heat Minimum On Time (Configuration→HEAT→MRT.H) and Heat Minimum Off Time (Configuration→HEAT→MOT.H) also apply.
Supply-Air Temperature Sensor (SAT)
The SAT Heat Mode Sensing (Configuration→HEAT→SAT→SAT.H) affects the Supply Air Temperature (Temperatures→AIR.T→SAT) value displayed. This configuration is accessible via the Scrolling Marquee on the SAT Heat Mode Sensing (Configuration→HEAT→SAT→SAT.H).
When the SAT Heat Mode Sensing (Configuration→HEAT→SAT→SAT.H) =DSBL, the Supply Air Temperature (Temperatures→AIR.T→SAT) value on the Scrolling Marquee and the CCN tables will be forced to zero when heat outputs come ON and for 5 minutes after. The default Supply Air Temperature (Temperatures→AIR.T→SAT) location is at the fan inlet, upstream of the heat section.
When the SAT Heat Mode Sensing (Configuration→HEAT→SAT→SAT.H) =ENBL, the Supply Air Temperature (Temperatures→AIR.T→SAT) sensor reading is displayed at the Scrolling Marquee and the CCN tables during heating mode. This setting should only be used if the original SAT sensor wires are removed from the Main Base Board (MBB) and replaced by an accessory SAT sensor located in the supply duct downstream of the heat section. There are then two supply air temperature limits that become active, the Maximum SAT Lower Level (Configuration→HEAT→SAT→SAM.L) the Maximum SAT Upper Level (Configuration→HEAT→SAT→SAM.U). Any time the supply air temperature rises above the Maximum SAT Lower Level (Configuration→HEAT→SAT→SAM.L) the heat staging will be limited to what is currently on and no additional stages can be added until the supply air temperature falls
below the Maximum SAT Lower Level (Configuration→HEAT→SAT→SAM.L). If the supply air temperature rises above the Maximum SAT Upper Level (Configuration→HEAT→SAT→SAM.U), then heating will be reduced by removing a heat stage. That stage can not be added
again until the Supply Air Temperature (Temperatures→AIR.T→SAT) falls below the Maximum SAT Lower Level (Configuration→HEAT→SAT→SAM.L). If the supply air temperature stays above the Maximum SAT Upper Level (Configuration→HEAT→SAT→SAM.U), then another stage will be removed after the Heat Stage Decrease Time (Configuration→HEAT→H.DEC).
In heating mode the PD control will maintain the Occupied Heat Set Point (Setpoint→OHSP) or the Unoccupied Heat Set Point (Setpoint→UHSP) by turning on or off the Stage 1 and Stage 2 Gas Heat at the Supply Fan Minimum Speed (Configuration→UNIT→FS.MN).
When the space temperature sensor detects the space temperature below the Occupied Heat Set Point (Setpoint→OHSP) or Unoccupied Heat Set Point (Setpoint→UHSP) and power is sent to the Integrated Gas Unit Controller (IGC) board. The heat staging is determined as described above and the Integrated Gas Controller (IGC) initiates the gas heat module start-up.
Gas Heat Start-Up
An LED (light-emitting diode) on the IGC board will be on during normal operation. A check is made to ensure that the rollout switch and limit switch are closed and the induced-draft motor is running. 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. When ignition occurs the IGC board will continue to monitor the condition of the rollout and limit switches, the Hall Effect sensor, as well as the flame sensor. 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
