Filter Replacement — To replace filters, open filter ac- cess door (marked with label). Remove inner access panel. Re- move plastic filter retainer in between filter tracks by sliding and pulling outward. Remove first filter by sliding it out of the opening in filter track. Locate filter removal tool, which is shipped next to the return air dampers. Use the filter removal tool to remove the rest of the filters.
Economizer Adjustment — Remove filter access panel. Check that
Economizer operation and adjustment are described in Sequence of Operation section on this page; and Step 10 — Make Outdoor Air Inlet Adjustments section on page 48.
Gas Heat — Verify gas pressures before turning on heat as follows:
1.Turn off
2.Connect pressure gage to supply gas tap, located on field- supplied manual shutoff valve (see Fig. 23 on page 29).
3.Connect pressure gage to manifold pressure tap on unit gas valve.
4.Supply gas pressure must not exceed 13.5 in. wg. Check pressure at
5.Turn on manual gas stop and initiate a heating demand. Jumper R to W1 in the control box to initiate heat. On VAV units, the RAT
6.Use the field test procedure to verify heat operation.
7.After the unit has run for several minutes, verify that in- coming pressure is 6.0 in. wg or greater, and that the man- ifold pressure is 3.5 in. wg. If manifold pressure must be adjusted refer to Gas Valve Adjustment section on page 93.
Sequence of Operation
NOTE: Unit is shipped with default values that can be changed through Service Tool, Building Supervisor, or Comfort- WORKS® software or using an accessory Remote Enhanced Display. See Table 35 for default values.
COOLING, CONSTANT VOLUME (CV) UNITS — On power up, the control module will activate the initialization software of the control board. The initialization software then reads DIP switch no. 1 position to determine CV or VAV oper- ation. Next, DIP switch no. 2 is read to determine if the control is thermostat or sensor type operation. If switch 2 is open, then sensors are employed. If switch no. 2 is closed, thermostat is employed. Initialization sequence clears all alarms and alerts, remaps the input/output database for CV operation, sets maxi- mum heat stages to 2, and sets maximum cool stages to 3. The control module reads DIP switch no. 3 and determines if the unit will use expansion board operation.
The first time power is sent to the control board after a power outage, power up takes 5 minutes plus a random 1 to 63 seconds.
The TSTAT function performs a thermostat based control by monitoring Y1, Y2, W1, W2, and G inputs. These functions control stages cool1, cool2, heat1, heat2, and indoor fan, re- spectively. If TSTAT function is NOT selected, the control de- termines the occupancy state on the Time Schedules or with re- mote occupied/unoccupied input. If Temperature Compensated
Start is active, the unit will be controlled as in the Occupied mode.
Table 36 lists the software link points addressable by DataPort™ and DataLINK™, Carrier devices that allow ac- cess to unit control by
The occupied or unoccupied comfort set points must be se- lected and the space temperature offset input will be used, if present. The Occupied Heat set point default value is 68 F. The Occupied Cool set point default value is 78 F. The Unoccupied Heat set point default value is 55 F. The Unoccupied Cool set point value is 90 F. The control board will set appropriate oper- ating mode and fan control. The control board will turn on in- door fan, if in Occupied mode, or determine if unit is in Unoc- cupied mode and the space temperature is outside of the unoc- cupied comfort set points, (Unoccupied Heat or Unoccupied Cool).
The control board will then monitor space temperature against comfort set points and control heating or cooling stages as required. If system is in the Occupied mode, the economizer will operate as required. If the system is in Unoccupied mode, the system will perform nighttime free cool and IAQ (indoor air quality)
The control board will operate economizer, run diagnostics to monitor alarms/alerts at all times, and respond to CCN com- munications to perform any configured network POC (product outboard control) functions such as time and
If thermostats are used to energize the G input, the control will turn on indoor fan without delay and open economizer dampers to minimum position. If thermostats are used to deen- ergize the G input, the control board will turn off indoor fan without any delay and close economizer dampers.
When cooling, G must be energized before cooling can op- erate. The control board determines if outdoor conditions are suitable for economizer cooling using the standard outdoor air thermistor. For economizer to function for free cooling, the en- thalpy must be low, the outdoor air must equal to or less than the High Outdoor Air Temperature Lockout (default is 65 F), the SAT
When Y1 input is energized, the economizer will be modu- lated to maintain SAT at the defined set point. The default is 55 F. When SAT is above the set point, the economizer will be 100% open. When SAT is below the set point, the economizer will modulate between minimum and 100% open position. When Y2 is energized, the control module will turn on com- pressor no. 1 and continue to modulate economizer as de- scribed above. If the Y2 remains energized and the SAT read- ing remains above the set point for 15 minutes, compressor no. 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 economizer cooling, the economizer will go to minimum position and cycle compressor no. 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 no. 1 and less than 45 F for compressor no. 2.) After a compressor is locked out, it can restart after normal time guard period.
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