Specifications

G) DX Cooling with Electric Heat
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. 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 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 62°F AND the minimum off time of 3 minutes has elapsed.
If the discharge air temperature falls below 52°F OR the optional refrigerant low limit switch trips OR electric
heat is engaged, the compressor shall be immediately disengaged, regardless of the minimum run timer
status. The compressor shall remain disengaged until the discharge air temperature rises above 52°F AND the
low limit switch opens AND electric heat is disengaged AND the minimum off time of 3 minutes has elapsed.
Heating Operation
There is a fixed 15-second delay between the engagement of each electric heat stage. Each electric heat
stage must be engaged for 1 minute (minimum ON timer) and each stage cannot be re-engaged for 1 minute
after being switched OFF (minimum OFF timer). These delays are built into the unit controller. Another built-in
timer prevents electric heat operation for 30 seconds after the compressor operation.
When the space temperature falls below the heating setpoint, electric heating shall be staged on to maintain
the space temperature. A proportional-integral control loop and built-in digital sequencer shall be used to
control up to 3 stages of electric heat. When the space temperature exceeds the heating setpoint, all electric
heat stages shall be staged OFF.
If the discharge air temperature exceeds 130°F, all electric heat stages shall be immediately disengaged,
regardless of the space temperature or the minimum ON timer. Electric heating shall remain disengaged until
the discharge air temperature falls below 110°F.
If the discharge air temperature falls below 52°F, all electric heat stages are immediately engaged, unless the
compressor is operating. All electric heat shall remain ON until the discharge air temperature rises above
55°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 52°F and remain closed
until the discharge air rises above 55°F.
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.
The outdoor air damper shall be controlled with a proportional control loop based upon the deviation from
setpoint. The outdoor air damper shall begin to modulate open from minimum position when the space
temperature exceeds the (space setpoint - 0.5°F). The outdoor air damper shall be fully open when the space
temperature rises 1.5°F above the setpoint. 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 52°F, the unit enters low limit mode. This shall drive the outdoor air
damper closed and immediately disengage the compressor. All stages of electric heat shall be staged on by
the integral timer; however, electric heat staging shall be delayed for 30 seconds if the compressor was in
operation. Normal unit operation shall resume when the discharge air temperature exceeds 55°F.
If 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 low limit switch opens AND the minimum off time (3 minutes) has elapsed.
7/1/03 Part Number 011-200001-003 Page 15