86
SERVICING
S-26 TESTING TEMPERATURE SENSORS
(COMFORTNET READY MODELS ONLY)
The DX16TC and DX18TC ComfortNet ready air conditioner
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:
WARNING
HIGH VOLTAGE
Disconnect ALL power before servicing or installing
this unit. 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 10kW, +/-10%, at 75°F. Replace
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™ 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
compatible outdoor unit and the CTK0* thermostat. A fully
communicating system offers advanced setup and diagnostic
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
WARNING
HIGH VOLTAGE
Disconnect ALL power before servicing or installing
this unit. 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).
