I. Head Pressure Control
Each unit has a fan cycling, outdoor thermostat to shut off the outdoor-fan motor(s) at 55 F. The head pressure control permits unit to operate with correct condensing tempera- tures down to 35 F outdoor-air temperature.
J. Motormaster III Control
The Motormaster III Solid-State Head Pressure Control is a ®eld-installed accessory fan speed control device actuated by a temperature sensor. It is speci®cally designed for use on Bryant equipment and controls the condenser-fan motor speed in response to the saturated condensing temperature. For out- door temperatures down to −20 F, it maintains condensing temperature at 100 F. Refer to the accessory Motormaster installation instructions for more information.
III. FIELD TEST OPERATION
The ®eld test program is initiated by moving up DIP switch no. 4 to the ``On'' position. The outdoor-air damper will close. The control allows 90 seconds for the damper to close in case it was in the full open position. Next, the indoor-fan con- tactor will be energized, and the outside-air damper will begin to open to its default value of 20% and stay at that po- sition for a short period of time. The outdoor-air damper will then open to its full open position and stay at that position for a short period of time. The outdoor-air damper will then close.
If the unit is equipped with power exhaust, stage 1 will be energized for 5 seconds. If the unit is con®gured for stage 2 of power exhaust, stage 2 will be energized for 5 seconds after the ®rst stage is deenergized.
The ®rst stage of heat will be energized for 30 seconds, after which the second stage heat will be energized for an addi- tional 30 seconds. Heat is then deenergized.
The last step is the Cooling mode. Outdoor-fan contactor no. 1 is energized. This is followed by each stage of cooling energized with a 10-second delay between stages. After this is complete, outdoor-fan contactor no. 2 is energized for 10 seconds.
The compressors will now deenergize, followed by the outdoor- fan contactors and indoor-fan contactors. If the unit is equipped with the Integrated Gas Control (IGC) board the indoor fan will operate for an additional 30 seconds after deenergizing the circuit.
Setting of the outdoor-air damper position is performed in con- junction with a shortened version of the ®eld test. Open DIP switch no. 4 and then no. 6.
The outdoor-air damper will close. The control allows 90 seconds for the damper to close in case it is in the full open position. Next, the indoor-fan contactor will energize. The outdoor-air damper will remain at 0% for 30 seconds. It will then move to the 10% position for another 30 seconds. This will be repeated at every 10% increment for 30 seconds until the damper reaches 100% open. Close DIP switch no. 4 during the 30 seconds immediately after the desired outdoor- air minimum damper position. The 30-second time period is to allow time where DIP switch no. 4 can be closed. The de- fault value of the minimum outdoor-air damper position is 20%. If the desired minimum position is 30%, allow the damper position to go to 10% for 30 seconds, then 20% for 30 seconds, and when it reaches 30% close DIP switch no. 4 during the 30-second period following the 30% position.
The minimum outdoor-air damper position is now set. Close DIP switch no. 6.
IV. INDOOR AIRFLOW AND AIRFLOW ADJUSTMENTS
CAUTION: For cooling operation, the recommended air¯ow is 300 to 450 cfm per each 12,000 Btuh of rated cooling capacity. For heating operation, the air¯ow must produce a temperature rise that falls within the range stamped on the unit rating plate.
A. Evaporator Fan Performance Adjustment
Be sure evaporator fans rotate in the proper direction. See Tables 8 and 9 for Fan Performance data. See Table 10 for Motor Limitation data. See Table 11 for air quantity limits.
IMPORTANT: Check to ensure that the unit drive matches the duct static pressure using Table 8.
Fan motor pulleys are factory set for speed shown in Table 1. To change fan speeds, change pulleys.
To align fan and motor pulleys (Fig. 34):
1.Shut off unit power supply.
2.Loosen fan shaft pulley bushing.
3.Slide fan pulley along fan shaft.
4.Make angular alignment by loosening motor from mount- ing plate.
5.Retighten pulley.
Fig. 34 Ð Evaporator-Fan Pulley Alignment and
Adjustment
B. Belt Tension Adjustment
To adjust belt tension:
1.Remove power to unit.
2.Remove motor mount nuts and bolts.
3.Loosen fan motor nuts. See Fig. 35.
