Heating Operation
The 48/50PG and 48/50PM unit’s heating operation consists of: demand, mode determination, staging request to satisfy the demand, and handling a request with the unit’s resources. These resources can be gas heat or electric heat. This section covers both gas heat units and electric heat units. The Type of Heat Installed (Configuration→HEAT→HT.TY) configuration will be factory set to 1 for gas units, 2 for electric heat units with heaters installed, and 0 for electric heat units without heat installed. The unit enters a heating mode based on a demand, decides how to satisfy the demand, executes its plan, and then leaves the heating mode.
Heating Mode Control
The heating HVAC mode (Run Status→MODE→HVAC=4), represents both types of heating (gas or electric) under all types of control. For the unit to be allowed to enter the heat mode, heat must be enabled (HT.TY = 1 or 2), and the Outdoor Air Temperature (Temperatures→AIR.T→OAT) must be less than the Heating Lockout Temp (Configuration→HEAT→HT.LO). Heat OAT Lockout (Run Status→MODE→H.LOC) displays when heat is locked out on outdoor temperature and therefore can not allow heat mode. The control will display if it is ok to select the heating mode (Operating Modes→HEAT →OK.HT= Yes).
Thermostat Control
For the unit to enter heating mode, three additional things must be true: the indoor fan must be ok to use, the mode changeover time guard must be expired, and there must be a heating demand (W1, W2). The unit will remain in heating until the heating demand is dropped or if any of the above conditions turn false. The heating mode can not officially end until all heat stages are off and the IGC fan request is dropped (on gas units without Humidi−MiZert).
Space Sensor Control
For the unit to enter heating mode, five additional things must be true: the indoor fan must be ok to use, the mode changeover time guard must be expired, the unit must have a valid space temperature, the W1 jumper must be installed, and there must be a heating demand. The unit will remain in heating for at least one minute and until the heat demand drops below −0.5_F or if any of the above conditions turn false. The heating mode can not officially end until all heat stages are off and the IGC fan request is dropped (on gas units without Humidi−MiZer).
Supply−Air Temperature Sensor (SAT)
The SAT Heat Mode Sensing (Configuration →HEAT→SAT→SAT.H) informs the unit if the supply air sensor has been relocated downstream of the heat section. This configuration affects the Supply Air Temperature (Temperatures →AIR.T→SAT) value displayed as listed below.
When 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 turn ON or OFF and for 5 minutes after. The default Supply Air Temperature location is at the fan inlet, upstream of the heat section.
When 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 two supply air temperature limits that affect heating operation, 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 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 back below SAM.L. If the supply air temperature rises above SAM.U, then heating will be reduced by removing a heat stage. That stage can not be added again until the Supply Air Temperature falls below SAM.L. If the supply air temperature stays above SAM.U, then another stage will be removed after the Heat Stage Decrease Time (Configuration →HEAT→H.DEC). If SAM.L and SAM.U are configured so that they are close together, the last stage of heat might cycle rapidly, slowed only by its minimum on and off−time requirements.
Staging Control
Once the unit is in a heating mode, it must decide what the demand is and how to satisfy. Based on the unit control configuration, requested heating stages (Run Status→HEAT→REQ.H) will be determined then passed to heat control to actually add the heating stages.
Thermostat Control
There are two ways of requesting stages when thermostat control is enabled: Traditional Thermostat control or Adaptive control. Traditional Thermostat control is used if the Thermostat Control Type (T.CTL) is set to 1, 2, or 3. Adaptive control is used if Thermostat Control (T.CTL) is set for 0.
T.CTL = 0 (Adaptive Control)
Stage timers and supply air temperature limits apply when determining the request for stages. The first request (REQ.C=1) comes immediately when the W1 input is active. 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.
T.CTL = 1, 2 or 3 (Traditional thermostat control)
Stage timers and supply air temperature limits do not apply when determining the request for stages. Request staging will follow the thermostat inputs directly. W1 will request one stage. W2 will request all stages.
48/50PG and PM
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