NOTE: The gas manifold is equipped with a plug located ap- proximately 5 in. down from the gas valve which may also be used to connect the manometer.

4.Turn on gas to unit.

5.Remove cover screw over regulator adjustment screw on gas valve. See Fig. 31.

6.Adjust regulator adjustment screw for a manifold pres- sure reading of 3.5 in. wg (high ®re on two-stage units). Turn adjusting screw clockwise to increase manifold pres- sure, or turn adjusting screw counterclockwise to decrease manifold pressure.

7.Replace cover screw.

8.Turn off gas to unit.

9.Remove manometer from pressure tap.

10.Replace pipe plug on gas valve or manifold.

11.Turn on gas to unit, and check for leaks.

F. Check Burner Flame and Ignition

Observe the unit heating operation. Watch the burner ¯ames through the access door to see if they are light blue and soft in appearance and if the ¯ames are approximately the same for each burner. See Fig. 32.

Fig. 32 Ð Monoport Burners

Main burners are factory set and should require no adjustment.

To check ignition of main burners and heating controls, move thermostat set point above room temperature and verify that the burners light and evaporator fan is energized. Check heat- ing effect, then lower the thermostat setting below the room temperature and verify that the burners and evaporator fan turn off.

Refer to Table 6 for the correct ori®ce to use at high altitudes.

G. Air¯ow and Temperature Rise

The heating section of each side of unit is designed and approved for heating operation within the temperature rise range stamped on the unit rating plate. Temperature rise range is also found in Table 1.

The heating operation air¯ow must produce a temperature rise that falls within the approved range.

Refer to Care and Maintenance section on page 28 to adjust heating air¯ow when required.

H. Safety Check of Limit Control

Limit control is located on the deck next to the evaporator fan. The control shuts off the gas supply and energizes the evaporator-fan motor and inducer motor if the unit overheats.

The recommended method of checking this limit control is to gradually block off the return air after the unit has been operating for a period of at least 5 minutes. As soon as the limit control functions, the return-air opening should be un- blocked to permit normal air circulation. By using this method to check the limit control, it can be established that the limit is functioning properly and the unit will ``fail-safe'' if there is a restricted circulating air supply or motor failure. If the limit control does not function during this test, the cause must be determined and corrected.

I. Heating Sequence of Operation

Heating, Units Without Economizer

When the thermostat calls for heating, terminal W1 is ener- gized. In order to prevent thermostat short-cycling, the unit is locked into the Heating mode for at least 1 minute when W1 is energized. The induced-draft motor is energized and burner ignition sequence begins. The indoor (evaporator) fan motor (IFM) is energized 45 seconds after a ¯ame is ignited. When additional heat is needed, W2 is energized and the high- ®re solenoid on the main gas valve (MGV) is energized. When the thermostat is satis®ed and W1 is deenergized, the IFM stops after a 45-second time-off delay.

Heating, Units With Economizer

When the thermostat calls for heating, terminal W1 is ener- gized. In order to prevent thermostat short-cycling, the unit is locked into the Heating mode for at least 1 minute when W1 is energized. The induced-draft motor is energized and the burner ignition sequence begins. The indoor (evaporator) fan motor (IFM) is energized 45 seconds after a ¯ame is ignited and the damper moves to the minimum position. If the two-position damper is used, the outdoor-air damper opens to the minimum position whenever the evaporator-fan runs. When additional heat is needed, W2 is energized and the high- ®re solenoid on the main gas valve (MGV) is energized. When the thermostat is satis®ed and W1 is energized, the IFM stops after a 45-second time-off delay. The economizer damper then moves to the fully-closed position. When using continuous fan, the damper will remain in the minimum position.

J. Limit Switches

Heating limit switch (LS) deenergizes the gas valve and the Integrated Gas Unit Controller (IGC) if the leaving-air tem- perature exceeds the maximum allowable temperature.

Normally-closed limit switch completes a circuit to the gas valve. Should the leaving-air temperature rise above the maximum allowable temperature, the limit switch opens, instantly closing the gas valve and stopping gas ¯ow to the burners. The inducer motor and the evaporator motor are en- ergized to cool heat exchanger.

When the air temperature at the limit switch drops to the low-temperature setting of the limit switch, the switch closes and completes the gas valve circuit. The electric-spark igni- tion system cycles and the unit returns to normal heating operation.

K. Rollout Switch

Rollout switch (RS) is a temperature-actuated automatic re- set switch connected in series with heating limit switch. The function of the switch is to close the main gas valve in the

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Bryant 581B Check Burner Flame and Ignition, Air¯ow and Temperature Rise, Safety Check of Limit Control, Limit Switches

581B specifications

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