Bryant 580G manual C. Cooling Capacity Control, Ð Cooling Capacity Staging Table, B.Gas Heating

compressor 2 will turn on. If Y2 is deenergized at any time, only the last stage of compression that was energized will be turned off. If outdoor conditions are not suitable for econo- mizer cooling, the economizer will go to minimum position and cycle compressors 1 and 2 based on demand from Y1 and Y2 respectively. The compressors will be locked out when the SAT temperature is too low (less than 40 F for compressor 1 and less than 45 F for compressor 2.) After a compressor is locked out, it can restart after normal time-guard period.

The compressor time delay function maintains a minimum off time of 5 minutes, a minimum on time of 10 seconds, and a minimum delay before starting the second compressor of 10 seconds.

When heating, the heat stages respond to the demand from W1 and W2 of the thermostat input. Heating and cool- ing will be mutually locked-out on demand on a ®rst call basis. The heating and the cooling functions cannot operate simultaneously.

C. Cooling Capacity Control

The cooling capacity staging is shown in Table 6.

Table 6 Ð Cooling Capacity Staging Table,

Units with 2 Compressors

STAGES	0	1	2	3
		ECONOMIZER
Compressor 1	Off	Off	On	On
Compressor 2	Off	Off	Off	On

NOTE: On units which require additional unloading, add suction pres- sure unloaders to compressor no. 1 only.

II.HEATING SECTION START-UP AND ADJUSTMENTS

CAUTION: Complete the required procedures given in the Pre-Start-Up section on page 20 before starting unit. Do not jumper any safety devices when operating the unit.

Verify gas pressures before turning on heat as follows:

a.Turn off manual gas stop.

b.Connect pressure gage to supply gas tap (See Fig. 10 on page 8).

c.Connect pressure gage to manifold pressure tap on gas valve.

d.Supply gas pressure must not exceed 13.5 in. wg. Check pressure.

e.Turn on manual gas stop and set thermostat to HEAT position. After the unit has run for several minutes, verify that incoming pressure is 5.0 in. wg or greater, and that the manifold pressure is 3.5 in. wg. If mani- fold pressure must be adjusted, refer to Gas Valve Adjustment section on page 25.

A. Checking Heating Control Operation

Start and check the unit for proper heating control operation as follows:

1.Turn on manual gas stop.

2.Set thermostat setting to HEAT position.

3.The evaporator fan and ®rst-stage heat will start im- mediately. If unit is equipped with 2 heaters, second- stage heat will energize upon a call for additional heat. Check for heating effect at supply diffusers.

4.The evaporator fan and heaters will cycle off with no delay after thermostat temperature is satis®ed.

B.Gas Heating

The gas heat units incorporate two separate systems to pro- vide gas heat. Each system incorporates its own induced draft motor, Integrated Gas Control (IGC) board, 2-stage gas valve, manifold, etc. The systems are operated in parallel, for example, when there is a call for ®rst stage heat, both induced draft motors operate, both gas valves are energized and both IGC boards initiate spark.

All of the gas heating control is performed through the IGC boards. The base module board serves only to initiate and terminate heating operation.

The base module board is powered by 24 vac. When the ther- mostat or room sensor calls for heating, power is sent from the base module board to W on each of the IGC boards. A light-emitting diode (LED) on the IGC board will be on dur- ing normal operation. A check is made to ensure that the roll- out switches and limit switches are closed and the induced draft motors are not running. The induced-draft motors are 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.

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 ¯ame sensor. If the unit is controlled through a room thermostat set for fan auto., 45 seconds after ignition occurs, the indoor-fan motor will be energized and the outdoor-air dampers will open to their minimum posi- tion. If for some reason the overtemperature 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 will not be interrupted to the burners and heating will con- tinue. Once modi®ed, the fan on delay will not change back to 45 seconds unless power is reset to the control.

When additional heat is required, W2 closes and initiates power to the second stage of the main gas valves. When the ther- mostat is satis®ed, W1 and W2 open and the gas valves close interrupting the ¯ow of gas to the main burners. If the call for W1 lasted less than 1 minute, the heating cycle will not terminate until 1 minute after W1 became active. If the unit is controlled through a room thermostat set for fan auto., the indoor-fan motor will continue to operate for an additional 45 seconds then stop and the outdoor-air dampers will close. If the over-temperature limit opens after the indoor motor is stopped within 10 minutes of W1 becoming inactive, on the next cycle the time will be extended by 15 seconds. The maxi- mum delay is 3 minutes. Once modi®ed, the fan off delay will not change back to 45 seconds unless power is reset to the control.

C. Power Exhaust Operation

The optional power exhaust packages are factory- or ®eld- installed with vertical units and optionally installed in the return air ductwork for horizontal applications. The stand- ard and the modulating power exhaust (used with non- modulatng to modulating conversion package) are the two packages offered. The modulating power exhaust package is equipped with a ®eld-adjustable static pressure controller to stage up to 4 power exhaust stages which will maintain a building static pressure. The blue controller located in the control box below the control board can be adjusted, by removing the covers and adjusting the set point dial to the desired building pressure. The blue controller monitors the 4 individual sequencers which activate the 4 individual power exhaust motors. The standard power exhaust package

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