Carrier 48PG20-28 specifications Operating Sequence, CO2 Sensor Standard Settings

3.Use the Up/Down button to select the preset number. See Table 29.

4.Press Enter to lock in the selection.

5.Press Mode to exit and resume normal operation.

outside air. The design should produce an air temperature somewhat near room conditions to prevent reheat of the air mixture. The energy recovery device should be interlocked with the heat to turn off the device when in the heat mode.

The custom settings of the CO2 sensor can be changed any- time after the sensor is energized. Follow the steps below to change the non-standard settings:

1.Press Clear and Mode buttons. Hold at least 5 seconds until the sensor enters the Edit mode.

2.Press Mode twice. The STDSET Menu will appear.

3.Use the Up/Down button to toggle to the NONSTD menu and press Enter.

4.Use the Up/Down button to toggle through each of the nine variables, starting with Altitude, until the desired setting is reached.

5.Press Mode to move through the variables.

6.Press Enter to lock in the selection, then press Mode to continue to the next variable.

Dehumidification of Fresh Air with DCV Control — Infor- mation from ASHRAE (American Society of Heating, Refrigeration, and Air Conditioning Engineers) indicates that the largest humidity load on any zone is the fresh air intro- duced. For some applications, a device such as a 62AQ energy recovery unit is added to reduce the moisture content of the fresh air being brought into the building when the enthalpy is high. In most cases, the normal heating and cooling processes are more than adequate to remove the humidity loads for most commercial applications.

This makes the control of the of the dehumidification device simple when using the enthalpy or differential enthalpy sensor. The enthalpy sensor or differential enthalpy sensor is installed on the equipment to determine economizer operation. The high enthalpy signal from the enthalpy sensor or differential enthalpy sensor can be used to turn on the outdoor air moisture removal device any time fresh air is required for the space.

The energy recovery device should be sized for maximum latent and sensible conditioning at maximum ventilation on a design day. A calculation for leaving-air temperature on a low ambient, low ventilation day should also be done to determine the mixed-air temperature of the return and pre-conditioned

Operating Sequence

COOLING, UNITS WITHOUT ECONOMIZER — When the thermostat calls for one stage of cooling, Y1 and G are en- ergized. The indoor-fan contactor (IFC) and compressor con- tactor(s) (C.A1 and C.B1 on three-compressor units or C.A1 only on two-compressor units), and outdoor-fan contactors (OFC1 and OFC2 when outdoor temperature is above LTS set- ting) are energized and the indoor-fan motor, compressor(s) (A1 and B1 on three compressor units or A1 only on two- compressor units), and outdoor fans controlled by OFC1 are started. If the outdoor temperature is above the setting of the low temperature switch, the outdoor fans controlled by OFC2 are also started.

If more cooling is required, the thermostat will call for a second stage of cooling, energizing Y2. This will allow relay CR1 to energize, which in turn energizes the compressor contactor (C.C1 on three-compressor units or C.B1 on two-compressor units). The second stage compressor (C1 on three-compressor units or B1 on two-compressor units is then started.

HEATING, UNITS WITHOUT ECONOMIZER NOTE: The 48PG20-28 units have 2 stages of heat.

When the thermostat calls for heating, power is sent to W on the IGC (integrated gas unit controller) board. An LED (light-emitting diode) on the IGC board will be on during nor- mal 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. To reset the control, break 24-v power to the thermostat.

Table 29 — CO2 Sensor Standard Settings

			VENTILATION	ANALOG	CO2	OPTIONAL	RELAY
SETTING	EQUIPMENT	OUTPUT	RATE		CONTROL RANGE	RELAY SETPOINT	HYSTERESIS
				OUTPUT
			(cfm/Person)		(ppm)	(ppm)	(ppm)
1		Proportional	Any	0-10V	0-2000	1000	50
				4-20 mA
2	Interface w/Standard	Proportional	Any	2-10V	0-2000	1000	50
	Building Control System			7-20 mA
3		Exponential	Any	0-10V	0-2000	1100	50
				4-20 mA
4		Proportional	15	0-10V	0-1100	1100	50
				4-20 mA
5		Proportional	20	0-10V	0- 900	900	50
				4-20 mA
	Economizer
6		Exponential	15	0-10V	0-1100	1100	50
				4-20 mA
7		Exponential	20	0-10V	0- 900	900	50
				4-20 mA
8	Health & Safety	Proportional	—	0-10V	0-9999	5000	500
				4-20 mA
9	Parking/Air Intakes/	Proportional	—	0-10V	0-2000	700	50
	Loading Docks			4-20 mA

LEGEND

PPM — Parts Per Million

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