·When the outdoor air quality is greater than the outdoor air quality set point (ppm)
High priority Ð When the priority is set to high, the IAQ set point controls the outside air damper exclusively, with no regard to comfort conditioning.
TIME GUARD CIRCUIT Ð The Time Guard function (built into the rooftop control board) maintains a minimum off time of 5 minutes, a minimum on time of 10 seconds, and a
CRANKCASE HEATER Ð Unit main power supply must remain on to provide crankcase heater operation. The crank- case heater in each compressor keeps oil free of refrigerant while compressor is off.
HEAD PRESSURE CONTROL Ð Each unit has a fan cy- cling, outdoor thermostat to shut off the
MOTORMASTER III CONTROL Ð The Motormaster
III
CAPACITY CONTROL, COOLING Ð The cooling capac- ity staging tables are shown in Tables 20 and 21.
Table 20 Ð Cooling Capacity Staging Table, CV Units
with 2 Compressors
|
| Stages |
|
|
| 0 | 1 | 2 | 3 |
| Economizer | |||
|
|
|
| |
Compressor 1 | off | off | on | on |
Compressor 2 | off | off | off | on |
|
|
|
|
|
NOTE: On CV units that require additional unloading, add suction pres- sure unloaders to Compressor 1 only.
Table 21 Ð Cooling Capacity Staging Table VAV Units
with 2 Compressors and 2 Unloaders*
|
|
|
| Stages |
|
|
| |
| 0 | 1 | 2 | 3 |
| 4 | 5 | 6 |
Compressor 1 | off | on | on | on |
| on | on | on |
Unloader 1 | off | on | on | off |
| on | on | off |
Unloader 2 | off | on | off | off |
| on | off | off |
Compressor 2 | off | off | off | off |
| on | on | on |
|
|
|
|
|
|
|
|
|
*40 ton units have only one unloader.
FIELD TEST Ð The ®eld test program is initiated by mov- ing up DIP switch no. 4 to the OPEN 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
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 additional 30 seconds. Heat is then deenergized.
The last step is the Cooling mode.
The compressors will now deenergize, followed by the
The ®eld test is then complete.
SERVICE
Before performing service or maintenance operations on unit, turn off main power switch to unit. Electrical shock could cause personal injury.
Service Access Ð All unit components can be reached through clearly labelled hinged access doors. These doors are not equipped with tiebacks, so if heavy duty servicing is needed, either remove them or prop them open to prevent accidental closure.
Each door is held closed with 3 latches. The latches are secured to the unit with a single
Fig. 45 Ð Door Latch
44