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 (ConfigurationHEATFOD.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 ModesHEATMS.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 (SetpointOHSP) or the Unoccupied Heat Setpoint (SetpointUHSP). See the Occupancy Determination section for factors that affect the Currently Occupied (Run StatusVIEWOCC) parameter. Heating Demand (Operating ModesHEATSPTDMD.H) is equal to the occupied or unoccupied set point minus the Space Temperature (Operating ModesHEATSPTSPT) [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 ModesHEATSPTDMD.H) plus the change in Spacetemp Trend (Operating ModesHEATSPTTRND) times the Heat Thermal Lag Factor (Operating ModesHEATSPTH.LAG) is greater than the SPT Heat Demand (+) Level (Operating ModesHEATSPTHT.PD) [DMD.H + change TRND * H.LAG > HT.PD].

The second method will add a stage of heating when Heat Demand (Operating ModesHEATSPTDMD.H) is greater that the

SPT Heat Demand (+) Level (Operating ModesHEATSPTHT.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 ModesHEATSPTDMD.H) plus the

change in Spacetemp Trend (Operating ModesHEATSPTTRND) times the Heat Thermal Lag Factor (Operating ModesHEATSPTH.LAG) is less than the SPT Heat Demand (-) Level (Operating ModesHEATSPTHT.ND) [DMD.H + change TRND * H.LAG < HT.ND].

The second method will remove a stage of heating when Heat Demand (Operating ModesHEATSPTDMD.H) is less that the SPT Heat Demand (-) Level (Operating ModesHEATSPTHT.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 (ConfigurationHEATH.INC) or removing

stages per Heat Stage Decrease Time (ConfigurationHEATH.DEC). Heat Minimum On Time (ConfigurationHEATMRT.H) and Heat Minimum Off Time (ConfigurationHEATMOT.H) also apply.

Supply-Air Temperature Sensor (SAT)

The SAT Heat Mode Sensing (ConfigurationHEATSATSAT.H) affects the Supply Air Temperature (TemperaturesAIR.TSAT) value displayed. This configuration is accessible via the Scrolling Marquee on the SAT Heat Mode Sensing (ConfigurationHEATSATSAT.H).

When the SAT Heat Mode Sensing (ConfigurationHEATSATSAT.H) =DSBL, the Supply Air Temperature (TemperaturesAIR.TSAT) 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 (TemperaturesAIR.TSAT) location is at the fan inlet, upstream of the heat section.

When the SAT Heat Mode Sensing (ConfigurationHEATSATSAT.H) =ENBL, the Supply Air Temperature (TemperaturesAIR.TSAT) 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 (ConfigurationHEATSATSAM.L) the Maximum SAT Upper Level (ConfigurationHEATSATSAM.U). Any time the supply air temperature rises above the Maximum SAT Lower Level (ConfigurationHEATSATSAM.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 (ConfigurationHEATSATSAM.L). If the supply air temperature rises above the Maximum SAT Upper Level (ConfigurationHEATSATSAM.U), then heating will be reduced by removing a heat stage. That stage can not be added

again until the Supply Air Temperature (TemperaturesAIR.TSAT) falls below the Maximum SAT Lower Level (ConfigurationHEATSATSAM.L). If the supply air temperature stays above the Maximum SAT Upper Level (ConfigurationHEATSATSAM.U), then another stage will be removed after the Heat Stage Decrease Time (ConfigurationHEATH.DEC).

In heating mode the PD control will maintain the Occupied Heat Set Point (SetpointOHSP) or the Unoccupied Heat Set Point (SetpointUHSP) by turning on or off the Stage 1 and Stage 2 Gas Heat at the Supply Fan Minimum Speed (ConfigurationUNITFS.MN).

When the space temperature sensor detects the space temperature below the Occupied Heat Set Point (SetpointOHSP) or Unoccupied Heat Set Point (SetpointUHSP) 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

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Carrier 48/50PD05 manual Supply-Air Temperature Sensor SAT, Gas Heat Start-Up

48/50PD05 specifications

The Carrier 48/50PD05 is a remarkable addition to Carrier's lineup of rooftop units, offering advanced cooling and heating solutions for commercial applications. Designed for medium-sized buildings, this unit is well-suited for both new installations and as a replacement for older systems, thanks to its versatile features and efficient performance.

One of the standout features of the 48/50PD05 is its energy efficiency. It incorporates state-of-the-art technology to achieve high Seasonal Energy Efficiency Ratios (SEER) and EER ratings, reducing operational costs while delivering superior comfort. The unit is also compliant with the latest energy regulations, making it an environmentally friendly choice for building owners concerned about sustainability.

The 48/50PD05 is equipped with a highly efficient scroll compressor, which not only enhances performance but also contributes to quiet operation. This is a significant advantage in commercial spaces where noise levels need to be kept in check for comfort and productivity. Additionally, the unit includes advanced airflow design, ensuring even distribution of conditioned air throughout the space.

Technologically, the Carrier 48/50PD05 features Carrier's Infinity Control system, which allows for precise control of indoor climate. This intelligent control mechanism can be integrated with smart building management systems, enabling users to monitor and manage energy use effectively. Wi-Fi connectivity is also available, providing remote access for real-time adjustments and diagnostics.

Durability is another characteristic of the 48/50PD05. Constructed with high-quality materials, the unit withstands various environmental conditions, ensuring longevity and reliability. Moreover, the modular design facilitates easy maintenance, making service procedures efficient and cost-effective.

In addition to cooling, the Carrier 48/50PD05 offers heating capabilities, often utilizing gas or electric heating options that can be tailored to the specific needs of a building. The unit can also be equipped with integrated economizers, allowing for free cooling during suitable outdoor conditions, further enhancing energy savings.

Overall, the Carrier 48/50PD05 stands out as a high-performance HVAC solution that combines efficiency, technology, and durability. It provides building owners with a versatile tool to ensure comfort while minimizing their environmental footprint. With a strong emphasis on energy savings and advanced control features, this rooftop unit is a smart investment for any commercial property.