7
thermostat is designed to operate up to one year on a set of bat-
teries. A battery indicator on the display warns when battery re-
placement is needed. If batteries are installed and the thermo-
stat is operating from 24 vac power, battery operation will oc-
cur only when 24 vac power is not present. The changeover
between 24 vac power and battery power is automatic.
Display Lighting —
The display has two levels of light-
ing, high level and low level. High level lighting comes on for
10 seconds when buttons are being pressed with 24 vac and
with batteries. Low level lighting is only available if the ther-
mostat is operated from 24 vac; it is not available with batter-
ies. The low level can be selected (see Option 18) for continu-
ous backlight.
Remote Sensor Temperature Display —
Press-
ing the
up
and
down
buttons simultaneously displays the tem-
perature of the sensor connected to the S1 and S2 terminals for
five seconds, then the thermostat returns to normal operation.
If the sensor is invalid, then the display shows "--" in the
large temperature display digits.
NOTE: Carrier sensors 33ZCT55SPT, 33ZCSENDAT,
33ZCSENSAT, and 33ZCSENOAT may be used for standard
space temperature sensor averaging. Sensors must be used as a
single sensor, 4 sensors or 9 sensors, with total sensor wiring
not to exceed 1,000 ft.
The remote space temperature 33ZCT55SPT sensor in-
cludes a button that, when pressed, shorts the S1 and S2 termi-
nals. If the thermostat is powered by 24 vac and Option 02 is
set to rS, pressing the button for two to five seconds has the
same effect as an occupied button press on the thermostat. This
button press is only recognized when the thermostat is powered
by 24 vac.
Timers —
Several timers that influence the thermostat’s op-
eration are listed below. If any of the timers is preventing the
equipment from turning on, the "on" icon will flash.
Five-Minute Compressor Timeguard —
This tim-
er prevents the Y1 output from turning on unless it has been off
for 5 minutes.
After a power cycle, a randomized delay will be added to
end of the timeguard timer to prevent multiple units from hit-
ting the power grid all at the same time. The randomization
timer will be between zero and five minutes. If a demand ex-
ists, compressor outputs will energize between 5 and 10 min-
utes after the power cycle. It can be defeated by simultaneously
pressing the
fan
and
up
keys.
Minimum On Timer —
Once the equipment has been
turned on, it must remain on for 3 minutes. A change in mode
or set point will cancel this timer.
Cycle Timer —
The number of equipment cycles per hour
is determined by configuration Option 16. Based on the selec-
tion of 4, 6 or 8 cycles per hour, this timer is set to 15, 10 or
8 minutes. This much time must elapse from the start of one
cycle before another cycle can start, imposing the cycles per
hour limits. It can be defeated for one cycle by simultaneously
pressing the
fan
and
up
keys.
Staging Timer —
The staging timer enforces a minimum
number of minutes for the current stage of equipment capacity
to be energized before staging up to the next level of capacity.
The number of minutes between each stage is configured by
the installer in software configuration Option 17.
TROUBLESHOOTING
Three system error messages may appear on the thermostat
screen indicating a problem with the thermostat’s operation.
See below for possible system error messages and their
meaning.
Space Temperature Sensor Failure —
If the
room temperature sensor fails, the temperature display will
show “--” (two dashes). If the space temperature is the average
of both the local and remote sensors (as configured in Option
5), and one of the sensors fails, the thermostat provides control
to the valid sensor only. The display will alternate every 10 sec-
onds between "--" for the invalid sensor and the reading from
the valid sensor.
Fan Failure —
The fan setting is specified by Option 36
and cannot be changed by the user. If Option 36 is set to ON,
and the
fan
button is pressed, an E7 error message will be dis-
played for three seconds and the fan selection will remain ON
and not be changed.
Memory Failure —
If there is an internal memory failure,
the temperature display will show “E4,” and the thermostat
needs to be replaced.
Equipment Outputs —
Table 3 can be used as a trou-
bleshooting tool for determining which outputs will be active
for a particular configuration and each operating mode.
Table 3 — Equipment Outputs
WIRING DIAGRAMS
System wiring diagrams are provided for typical Carrier
equipment. See Fig. 6-24.
EQUIP
CONFIG
(Option
01
Setting)
COOL
STAGE
1
COOL
STAGE
2
HEAT
STAGE
1
HEAT
STAGE
2
HEAT
STAGE
3
EM
HEAT
AC
Y1
Y1,
Y2
W
W,
O/B
—
O/B
HP
Option
10=C
Y1,
O/B
Y1,
Y2,
O/B
Y1
Y1,
Y2
Y1,
Y2,
W
W
HP
Option
10=H
Y1
Y1,
Y2
Y1,
O/B
Y1,
Y2,
O/B
Y1,
Y2,
W,
O/B
W
H
—
—
W
W,
O/B
—
O/B
C
Y1
Y1,
Y2
—
—
—
—
WSHP
Y1,
O/B
Y1,
Y2,
O/B
Y1
Y1,
Y2
Y1,
Y2,
W
W
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