Carrier 48/50AJ specifications Appendix D Mode Selection Process

APPENDIX D — MODE SELECTION PROCESS

The following section is to be used in conjunction with Fig. 4 on page 34. To help determine why the unit controls are in a certain mode, the programming logic is provided below. The software will proceed, step by step, until a mode is reached. If an “If” statement is true, then that mode will be en- tered. The “Else” statement refers to other possible choices.

If the System Mode is OFF:

{If the fire shut down input (Inputs→FIRE→FSD) is in “alarm”:

HVAC mode:	("Fire Shut Down ") OFF
Else
HVAC mode:	("Disabled ") OFF}

Else If: The rooftop is not in “factory test” and a fire smoke-control mode is “alarming”:

{If the pressurization input (Inputs→FIRE→PRES) is in “alarm”:

HVAC mode: ("Pressurization ")

Else If the evacuation input (Inputs→FIRE→EVAC) is in “alarm”:

HVAC mode: ("Evacuation ")

Else If the smoke purge input (Inputs→FIRE→PURG) is in “alarm”:

HVAC mode: ("Smoke Purge ")}

Else If: Someone changed the machine’s

control type (Configuration→UNIT→C.TYP) during

run time, a 15 second delay is called out:

{ HVAC mode: ("Disabled ") OFF}

Else If: The System Mode is TEST:

{	HVAC mode:	("Test	")}
	Else If: The “soft stop” command (Service Test→S.STP)
	is forced to YES:
{	HVAC mode:	("SoftStop Request")}
	Else If: The remote switch config (Configuration→
	UNIT→RM.CF)=2; “start/stop”, and the remote
	input state (Inputs→GEN.I→REMT)=ON:
{	HVAC mode:	("Rem. Sw. Disable") OFF}
	Else If: Configured for static pressure control
	(Configuration→SP→SP.CF = 1,2) and the static
	pressure sensor (Pressures→AIR.P→SP) fails:
{	HVAC mode:	("Static Pres.Fail") OFF}

Else If: Configured for supply fan status monitoring (Configuration→UNIT→SFS.M = 1,2) and configured to shut the unit down on fan status fail (Configuration→UNIT→SFS.S = YES)

{	HVAC mode:	("Fan Status Fail ") OFF}
Else If: The unit is just waking up from a power reset
{	HVAC mode:	("Starting Up ") OFF}
Else If: A compressor is diagnosed as being “Stuck On”
{	HVAC mode:	("Comp. Stuck On ")
Else	The control is free to select the normal heating/

cooling HVAC modes:

{ HVAC mode: ("Off ")

—The unit is off and no operating modes are active.

HVAC mode: ("Tempering Vent ")

—The economizer is at minimum vent position but the supply air temperature has dropped below the tempering vent set point. Gas heat is used to temper the ventilation air.

HVAC mode: ("Tempering LoCool")

—The economizer is at minimum vent position but the combination of the outside-air temperature and the economizer position has dropped the supply-air temperature below the tempering cool set point. Gas heat is used to temper the ventilation air.

HVAC mode: ("Tempering HiCool")

—The economizer is at minimum vent position but the combination of the outside air temperature and the economizer position has dropped the supply air temperature below the tempering cool set point.

Gas heat is used to temper the ventilation air.

HVAC mode: (“Re-Heat”)

—The unit is operating in reheat mode.

HVAC mode: (“Dehumidification”)

—The unit is operating in dehumidification mode.

HVAC mode: ("Vent ")

—This is a normal operation mode where no heating or cooling is required and outside air is being delivered to the space to control IAQ levels.

HVAC mode: ("Low Cool ")

—This is a normal cooling mode when a low cooling demand exists.

HVAC mode: ("High Cool ")

—This is a normal cooling mode when a high cooling demand exists.

HVAC mode: ("Low Heat ")

—This is a normal heating mode when a low heating demand exists.

HVAC mode: ("High Heat ")

—This is a normal heating mode when a high heating demand exists.

HVAC mode: ("Unocc. Free Cool")

—In this mode the unit will operate in cooling but will be using the economizer for free cooling. Entering this mode will depend on the status of the outside air. The unit can be configured for outside air changeover, differential dry bulb changeover, outside air enthalpy changeover, differential enthalpy changeover, or a custom arrangement of enthalpy/dewpoint and dry bulb. See the Economizer section for further details.}

NOTE: There is also a transitional mode whereby the machine may be waiting for relay timeguards to expire before shutting the machine completely down:

HVAC mode: ("Shutting Down ")

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