Head Pressure Control - Carrier 48FP Controls Operation And Troubleshooting

time in minutes prior to the scheduled unoccupied time) during
which expanded heating and cooling set points can be used.
Adaptive optimal stop utilizes space temperature, an expanded
occupied set point, and a "K" factor to calculate stop time off-
set. The amount (F) to expand the occupied set point is user
configurable. Like adaptive optimal start, the control corrects
itself for optimal operation by adjusting the "K" factor as
required.
HEATING
NOTE: The heating algorithms on the units will only run when
the supply-air (evaporator) fan is on. Two-stage factory-
installed gas heat is standard on the 48FP,JP,NP units.
When the unit is in the Heating mode, room terminals must
be fully open. The room terminals should be controlled by the
heat interlock relay (HIR) function on VAV applications.
NOTE: HIR not applicable on units using DAV applications.
During heating, the economizer dampers will be at the min-
imum damper position during Occupied Heating mode, and
will be fully closed during unoccupied heating.
Occupied VAV Operation — Heating is primarily used for
morning warm-up or occupied space heating with the heater
being staged to maintain desired return-air temperature. If the
unit is in morning warm-up, the return-air temperature is read
and compared to the occupied heating set point. The unit con-
trols will compare the calculated supply-air temperature set
point to the actual supply-air temperature to compute the num-
ber of stages required to satisfy the conditions. Once morning
warm-up is completed and the unit is in Occupied mode, heat
will not be activated again unless the Occupied Heating mode
has been selected.
Occupied CV Operation — The heater is staged to prevent the
occupied space temperature from falling below the desired set
point. The control reads the space temperature and computes
the supply-air temperature necessary to heat the space to the
heating set point. The unit controls will compare the calculated
supply-air temperature set point to the actual supply-air tem-
perature to compute the number of stages required to satisfy the
conditions.
Morning Warm-Up (VAV Only) — Morning warm-up occurs
when the adaptive optimal start (AOS) algorithms start the unit
before the occupied start time, and the unit has a heating de-
mand. The morning warm-up control uses the occupied heating
set point for controlling heat stages. Once the return air reaches
the set point, heating will be shut off.
When the heating demand is satisfied, the warm-up condi-
tion will terminate. The unit may reenter morning warm-up if
there is another call for heat before the start of the occupied pe-
riod. Morning warm-up can continue into the occupied period
as long as there is a need for heat, even if occupied heating is
not enabled.
NOTE: The economizer dampers will be fully closed during
morning warm-up, except when morning warm-up continues
into the occupied period. If morning warm-up continues into
the occupied period, the dampers will open to the minimum
position to provide ventilation air.
Room terminals must go to the fully open position when the
unit enters the heating mode. The terminals should be con-
trolled by the HIR function. When the unit goes into heating
mode, the HIR contacts are energized which open the room
terminals.
NOTES:
1. Morning warm-up is initiated before the unit schedule
designated occupied time. Unit must have a valid
occupancy schedule program or be connected to the
network or DAV with occupancy schedules.
2. HIR is not applicable on units using DAV applications.
Economizer Minimum Position — The control has the capa-
bility of maintaining the minimum economizer position based
on 3 inputs. The 3 inputs are minimum position, outdoor-
air cfm, and IAQ set points. The
used to configure the control for the minimum position of the
economizer.
Indoor-Air Quality (IAQ) — The unit may be configured to
control the occupied space indoor-air quality by maintaining a
constant cfm of outdoor air and/or an allowable level of unde-
sirable gases or vapors (CO
stallation of appropriate sensors and/or accessories. The econo-
mizer dampers will modulate to maintain the user-defined set
points.
An alert will be generated after 10 minutes if the air quality
level has not been reduced below the set point.
The indoor air quality feature has 3 priority levels as follows
(Refer to Indoor Air Quality [IAQ] and Outdoor Air Control
[OAC] sections on pages 25 and 27 for more details):
Priority Level 1 — This is the highest level of priority for
indoor air quality. When the IAQ set point is exceeded, the
IAQ algorithms adjust the economizer damper position to
purge the controlled space of CO
Priority Level 2 — This is a medium level priority and pro-
vides for some occupied space comfort overrides. The IAQ
algorithms adjust the economizer damper position to purge the
controlled space of CO
following comfort overrides may take precedence:
• space temperature
• supply-air temperature (VAV)
• space humidity
Priority Level 3 — This is the lowest priority level. When the
IAQ set point is exceeded, an alert is generated. Alert can be
viewed at the HSIO and is broadcast on the CCN network (if
applicable), but no other action is taken.
NOTE: Consult the latest updated issue of ASHRAE (Ameri-
can Society of Heating, Refrigeration, and Air Conditioning
Engineers) Standard 62 when determining required set points
for indoor air quality (ASHRAE 62, Ventilation for Acceptable
Indoor-Air Quality section).
Head Pressure Control —
trols the condenser fans to maintain the lowest condensing tem-
perature and the highest operating efficiency possible. The con-
denser fan stages are configured to react to either saturated con-
densing temperatures (SCT) or refrigerant pressure sensors, or
can be controlled by the lead compressor.
Unit sizes 034-038 have 2 stages of fan control. The stage 2
fan contactor OFC1 will cycle in response to the higher SCT of
the 2 circuits. Unit sizes 044-078 have 3 fan stages. Fan contac-
tors OFC1 and OFC2 will respond to their associated circuit
SCT. Unit sizes 088 and 104 have 4 fan stages with individual
circuit stage control.
A low ambient head pressure control option is also included
standard on all units as an additional feature to allow fan cy-
cling on the first stage. The first stage of head pressure control
is cycled in the same manner as the Motormaster® II control.
See Tables 51A and 51B.
Sizes 034-078: The highest SCT is used to control the con-
denser (outdoor) fan motor(s) (OFM) controlled by the head
pressure control relay (MMR). See Table 52 for fan control
points. If either stage 2 contactor (OFC1 or OFC2) is energized
in addition to MMR, then MMR will be locked in the ener-
gized mode.
56
VENT function is
, CO, formaldehyde, etc.) with in-
2
or other contaminants.
2
or other contaminants. However, the
2
The microprocessor con-