SERVICING
71
S-26 TESTING TEMPERATURE SENSORS
(COMFORTNET READY MODELS ONLY)
The DX16TC and DX18TC ComfortNet ready air condi-
tioner models are factory equipped with an outdoor air
temperature (OAT) sensor. The OAT sensor allows the
outdoor air temperature to be displayed on the CTK0*
thermostat when used with the ASXC and DSXC models.
The DZ16TC and DZ18TC ComfortNet ready heat pump
models are equipped with both an outdoor air temperature
(OAT) sensor and an outdoor coil temperature (OCT)
sensor. The OAT provides the balance point temperature
in heat pump systems (air handler w/electric heat + heat
pump) and dual fuel systems. The OCT sensor is provides
the outdoor coil temperature and is used in determining
defrost cycles.
To check either the outdoor air or outdoor coil temperature
sensors:
HIGH VOLTAGE!
Disconnect ALL power before servicing
or installing. Multiple power sources
may be present. Failure to do so may
cause property damage, personal injury
or death.
1. Disconnect power to the air conditioner or heat pump.
2. Disconnect the sensor from the unitary (UC) control.
3. Connect an ohmmeter across the sensor terminals. The
ohmmeter should read be 10k
Ω
, +/-10%, at 75°F. Re-
place the sensor if the sensor is open, shorted, or outside
the valid resistance range.
T, °F
RW@T
T, °F
RW@T
T, °F
RW@T
T, °F
RW@T
T, °F
RW@T
-40
336,000
5
72,940
50
19,903
95
6,530
140
2,488
-31
242,700
14
55,319
59
15,714
104
5,327
149
2,083
-22
177,000
23
42,324
68
12,493
113
4,370
158
1,752
-13
130,400
32
32,654
77
10,000
122
3,603
167
1,480
-4
97,060
41
25,396
86
8,056
134
2,986
176
1,255
Ohm Reading of Communicating Outdoor Unit Sensors
S-40A DVPTC/MBVC ELECTRONIC BLOWER/
HEATER CONTROL
Description
The DVPTC and MBVC models utilize an electronic control
that provides ECM blower motor control and control of up to
two electric heat sequencers. The control has thermostat
inputs for up to two stages of cooling, two stages of electric
heat, reversing valve, and dehumidification. Control input is
24VAC.
All dipswitches necessary to setup cooling, heat pump, and
electric heat airflow are fully integrated into the control.
Dehumidification is enabled/disabled via an on-board
dipswitch.
Features
The new air handler control includes advanced diagnostic
features with fault recall, estimated CFM display via on-board
LED, and ComfortNet
TM
ready. Diagnostics includes heater
kit selection diagnostics, open fuse, internal control fault,
data errors, and blower motor faults. Data errors are not
included in the fault recall list. Diagnostic error codes are
displayed on a single red LED.
The estimated CFM is displayed as a flashing green LED. The
LED flashes once for each 100 CFM.
The DVPTC/MBVC air handlers may be used in a fully
communicating ComfortNet system when matched with a
compatiable outdoor unit and the CTK0* thermostat. A fully
communicating system offers advanced setup and diagnos-
tic features.
Basic Operation
The air handler control receives thermostat inputs either from
a standard 24VAC thermostat or the CTK0* ComfortNet
thermostat. For cooling and heat pump operation, the control
operates the variable speed blower motor at the demand as
determined from the thermostat input(s). If a demand for
electric heat is received, the control will provide a 24VAC
output for up to two electric heat sequencers.
Troubleshooting
Motor Control Circuits
HIGH VOLTAGE!
Disconnect ALL power before servicing
or installing. Multiple power sources
may be present. Failure to do so may
cause property damage, personal injury
or death.
1. Turn on power to air handler or modular.
WARNING
Line Voltage now present.
2. Check voltage between pins 1 and 4 at the 4-wire motor
connector on the control board.
See Electrical Checks
- Low Voltage Control Circuits section (S-16H).
