56
5 equivalent duct diameters downstream of the unit. Also, care
should be taken to avoid placing the thermistor within a direct
line-of-sight of the heating element to avoid radiant effects.
Run a new two-wire conductor cable from the control box
through the low voltage conduit into the space inside the build-
ing and route the cable to the new sensor location.
Installing a New Sensor
A field-provided duct-mount temperature sensor (Carrier P/N
33ZCSENPAT or equivalent 10,000 ohms at 25°C NTC [nega-
tive temperature coefficient] sensor) is required. Install the sen-
sor through the side wall of the duct and secure.
Re-Using the Factory SAT Sensor
The factory sensor is attached to one of the supply fan hous-
ings. Disconnect the sensor from the factory harness. Drill a
hole insert the sensor through the duct wall and secure in place.
Attach the new conductor cable to the sensor leads and termi-
nate in an appropriate junction box. Connect the opposite end
inside the unit control box at the factory leads from MBB J8
terminals 11 and 12 (PNK) leads. Secure the unattached PNK
leads from the factory harness to ensure no accidental contact
with other terminals inside the control box.
MORNING WARM UP
Morning Warm Up, a Linkage mode, is a period of time that
assists CCN linkage in opening up downstream zone dampers
for the first heating cycle of a day.
The Morning Warm Up Period is CCN linkage mode “2” and is
relayed in the following conditions:
• Temperature Compensated Start Mode is active AND Heat
Mode in effect AND LAT is warm enough or is to be ig-
nored due to placement.
• The unit just went into occupied mode and there has been
no cooling mode yet and a heat cycle occurs or was in
progress when the unit went occupied.
In both cases, if and when the heat mode terminates, a heat cy-
cle has occurred and any subsequent heat cycles will not be
treated as a morning warm up period.
TEMPERING MODE
In a vent or cooling mode, the rooftop may encounter a situa-
tion where the economizer at minimum position is sending
cold outside air down the ductwork of the building. Therefore,
it may be necessary to bring heat on to counter-effect this low
supply-air temperature. This is referred to as the tempering
mode.
Setting up the System
The relevant setpoints for Tempering are located at the local
display under
Setpoints
:
Operation
First, the unit must be in a vent mode, a low cool mode, or a
high cool HVAC mode to be considered for a tempering mode.
Secondly, the tempering mode is only allowed when the roof-
top is configured for staged gas (
Configuration
HEAT
HT.CF
=3
).
If the control is configured for staged gas, the control is in a vent,
low cool, or high cool HVAC mode, and the rooftop control is in
a situation where the economizer must maintain a minimum po-
sition, then the evaporator discharge temperature (EDT) will be
monitored. If the EDT falls below a particular trip point then the
tempering mode may be called out:
HVAC mode = “Tempering Vent”
HVAC mode = “Tempering LoCool”
HVAC mode = “Tempering HiCool”
The decision making/selection process for the tempering trip
setpoint is as follows:
• If an HVAC cool mode is in effect, then the vent trip point
is
T.CL
.
• If in a pre-occupied purge mode (
Operating Modes
MODE
IAQ.P=
ON
), then the trip point is
T.PRG
.
• If in an occupied mode (
Operating Modes
MODE
IAQ.P
=ON
), then the trip point is
T.V.OC
.
• For all other cases, the trip point is
T.V.UN
.
NOTE: The unoccupied economizer free cooling mode does not
qualify as a HVAC cool mode as it is an energy saving feature and
has its own OAT lockout already. The unoccupied free cooling
mode (HVAC mode = Unocc. Free Cool) will override any unoc-
cupied vent mode from triggering a tempering mode.
If OAT is above the chosen tempering setpoint, tempering will
not be allowed. Additionally, tempering mode is locked out if
any stages of mechanical cooling are present.
A minimum amount of time must pass before calling out any
tempering mode. In effect, the EDT must fall below the trip
point value –1°F continuously for a minimum of 2 minutes. Al-
so, at the end of a mechanical cooling cycle, there must be a
minimum 10 minutes of delay allowed before considering tem-
pering during vent mode in order to allow any residual cooling
to dissipate from the evaporator coil.
If the above conditions are met, the algorithm is free to select
the tempering mode (MODETEMP). If a tempering mode be-
comes active, the modulating heat source (staged gas) will at-
tempt to maintain leaving-air temperature (LAT) at the temper-
ing setpoint used to trigger the tempering mode. The technique
for modulation of setpoint for staged gas and hydronic heat is
the same as in a heat mode. More information regarding the
operation of heating can be referenced in the Heating Control
section.
Recovery from a tempering mode (MODETEMP) will occur
when the EDT rises above the trip point. On any change in
HVACMODE, the tempering routine will re-assess the temper-
ing setpoint which may cause the control to continue or exit
tempering mode.
Static Pressure Control
Variable air volume (VAV) air-conditioning systems must pro-
vide varying amounts of air to the conditioned space. As air
terminals downstream of the unit modulate their flows, the unit
must maintain control over the duct static pressure in order to
accommodate the needs of the terminals and meet the varying
combined airflow requirement.
The static pressure control routine is also used on CV units
with VFD for staged air volume. The fan is controlled at dis-
crete speeds through the VFD by the unit
Comfort
Link controls
based on the operating mode of the unit.
A 48/50A3,A5 unit equipped with a duct pressure control sys-
tem is provided with a variable frequency drive (VFD) for the
supply fan. The speed of the fan can be controlled directly by
the
Comfort
Link controls. A transducer is used to measure duct
static pressure. The signal from the transducer is received by
the ECB-2 board and is then used in a PID control routine that
outputs a 4 to 20 mA signal to the VFD.
Generally, only VAV systems utilize static pressure control. It is
required because as the system VAV terminals modulate closed
when less air is required, there must be a means of controlling
ITEM
EXPANSION
RANGE
UNITS
CCN
POINT
DEFAULT
T.PRG
Tempering
Purge SASP
–20 to 80
dF
TEMPPURG
50
T.CL
Tempering in
Cool SASP
5 to 75
dF
TEMPCOOL
5
T.V.OC
Tempering Vent
Occ SASP
–20 to 80
dF
TEMPVOCC
65
T.V.UN
Tempering Vent
Unocc. SASP
–20 to 80
dF
TEMPVUNC
50
Summary of Contents for WEATHERMAKER 48A2020
Page 112: ...112 Fig 20 Typical Main Control Box Wiring Schematic 48 50A Units ...
Page 113: ...113 Fig 21 Typical Auxiliary Control Box Wiring Schematic ...
Page 114: ...114 Fig 22 Typical 2 Stage Gas Heat Wiring Schematic Size 060 Units Shown ...
Page 115: ...115 Fig 23 Typical Staged Gas Heat Wiring Schematic Size 060 Units Shown TO NEXT PAGE ...
Page 116: ...116 Fig 23 Typical Staged Gas Heat Wiring Schematic Size 060 Units Shown cont ...
Page 117: ...117 Fig 24 Typical Electric Heat Control Schematic 50 Series Size 060 Units Shown ...
Page 118: ...118 Fig 25 Typical Controls Option Wiring Schematic SW1 SW2 OR DEHUMIDIFY SWITCH ...
Page 119: ...119 Fig 26 Typical Power Schematic 48 50A2 A3 A4 A5 060 Unit Shown ...
Page 120: ...120 Fig 27 Typical Power Schematic of Greenspeed Low Ambient Option 48 50A 060 Unit Shown ...
Page 121: ...121 Fig 28 Typical Small Chassis Component Location Size 020 035 Units ...
Page 122: ...122 Fig 29 Typical Large Chassis Component Locations Size 040 060 Units ...
Page 185: ...185 APPENDIX C VFD INFORMATION cont Fig F Internal Enclosure Fan Replacement A48 7716 ...