Specifications

H) DX Cooling with Wet Heat, Damper Control
Fan Operation
The supply fan shall run continuously in the occupied and tenant (unoccupied) override modes. The fan shall
cycle with calls for cooling or heating in the unoccupied mode.
Cooling Operation
When the space temperature exceeds the cooling setpoint, the compressor shall be started and the face &
bypass damper driven fully open (face position). The compressor shall run until the space temperature falls
0.5°F below the cooling setpoint. Compressor operation shall be controlled with an integrated run timer such
that once engaged, the compressor shall operate for a minimum of 2 minutes before disengaging. This run
timer also provides a 3-minute minimum OFF time delay (anti short-cycle timer).
If the outdoor air temperature falls below 59°F, the compressor shall be disengaged when the minimum run
time of 2 minutes is complete. The compressor shall remain disengaged until the outdoor air temperature
exceeds 61°F AND the minimum off time of 3 minutes has elapsed.
If the heating coil low limit switch closes OR the optional refrigerant low limit switch closes, OR the discharge
air temperature falls below 50°F, the compressor shall be immediately disengaged, regardless of the minimum
run timer status. The compressor shall remain disengaged until the heating coil low limit switch is open AND
the optional refrigerant low limit switch is open AND the discharge air temperature is above 52°F AND the
minimum off time of 3 minutes has elapsed.
Heating Operation
When the space temperature falls below the heating setpoint, a proportional-integral control loop shall position
the face and bypass damper to maintain the space temperature. When the space temperature exceeds the
heating setpoint, the face and bypass damper shall close (bypass).
If the discharge air temperature fall below 53°F, OR the heating coil low limit thermostat closes, the face and
bypass damper shall drive open (face). This damper shall return to normal control when the discharge air
temperature exceeds 55°F AND the low limit thermostat is opened.
Optional End-of-Cycle Valve Operation
A normally open, 2-position valve with return on power failure is optionally used for end-of-cycle (EOC) control.
When the space temperature falls below the heating setpoint, the EOC valve shall open. The EOC valve shall
remain open until the space temperature exceeds the heating setpoint by 2°F.
When the outdoor air temperature falls below 40°F or the heating coil low limit switch closes, the EOC valve
shall open, regardless of space conditions. This valve shall remain open until the outdoor air temperature rises
above 44°F AND the heating coil low limit switch is open.
If the discharge air temperature exceeds 130°F, the EOC valve shall be closed, regardless of other conditions.
The EOC valve shall remain closed until the discharge air temperature falls below 110°F.
Outdoor Air Damper Control
The outdoor air damper shall be closed in the unoccupied mode, regardless of the space temperature
conditions.
The outdoor air damper shall be closed if the discharge air temperature falls below 53° OR the heating coil low
limit thermostat closes. This damper shall remain closed until the discharge air temperature rises above 55°F
AND the heating coil low limit thermostat is open.
The outdoor air damper shall be closed if the space temperature falls more than 3°F below the heating
setpoint. The damper will not open until the space temperature rises within 2°F of the heating setpoint.
The outdoor air damper shall close to minimum position when the outdoor air temperature exceeds 68°F OR
the room temperature falls more than below the heating setpoint.
The outdoor air damper shall be controlled with a proportional control loop based upon the discharge air
temperature. The outdoor air damper shall begin to modulate open from minimum position when the discharge
air temperature exceeds 55°F and shall be fully open at 59°F. Except as noted in the paragraphs above, the
outdoor air damper shall not close beyond minimum position during occupied operation.
Safeties - Low Limit Conditions
If the discharge air temperature falls below 53°F OR the heating coil low limit thermostat closes, the unit enters
ventilation low limit mode. This shall drive the outdoor air damper closed and forces the face and bypass
damper fully open (face). These dampers shall return to normal control when the discharge air temperature
exceeds 55°F AND the heating coil low limit thermostat is open.
If the discharge air temperature falls below 50°F OR the heating coil low limit thermostat closes OR the
optional refrigerant low limit switch closes, the unit enters refrigeration low limit mode. This shall immediately
disengage the compressor, regardless of the minimum on timer status. The compressor shall not be allowed to
operate until the discharge air temperature exceeds 52°F AND the heating coil low limit thermostat is open
AND the optional refrigerant low limit switch is open AND the minimum off time has elapsed.
7/1/03 Part Number 011-200001-003 Page 16