Carrier 25VNA8 Instruction Manual download pdf (Page 17)

Refer to Table 5 and Fig. 21 and 22 for resistance values versus

temperature.

Table 5 – 10K/50Kohm Resistance Values vs Temperature

10Kohm

_C(_F)

TEMPERA TURE RESIST ANCE (ohms)

25.0 (77.0) 10.0 + / --- 2.3%

0.0 (32.0) 32.6 + / --- 3.2%

-28.0 (-18.4) 85.5 + / --- 3.4%

50Kohm

125.0 (257.0) 1.7 + / --- 1.6%

75.0 (167.0) 7.40 + / --- 2.0%

25.0 (77.0) 50.0 + / --- 2.3%

0 20 40 60 80 100 120

TEMPERATURE (DEG. F)

RESISTANCE (KOHMS)

THERMISTOR CURVE

A91431

Fig. 21 -- 10K Thermistor Resistance Versus Temperatur e

100

150

200

250

300

350

400

450

020406080100120

RESISTANCE (KOHMS)

TEMPERATURE (°°F)

50K THERMISTOR

A14022

Fig. 22 -- 50K Thermistor Resistance Versus Temperatur e

If the outdoor air or coil thermistor should fail, the control will

flash the appropriate fault code (see Table 7).

IMPORTANT: The outdoor air thermistor, coil thermistor and

suction thermistor should be factory mounted in the final

locations. Check to ensure thermistors ar e mounted properly

(See Fig. 23, 24, 25 and 26).

Thermistor Sensor Comparison

The control continuously monitors and compares the outdoor air

temperature sensor and outdoor coil temperature sensor to ensure

proper operating conditions. The comparison is:

S In cooling if the outdoor air sensor indicates  10_F( 5.6_C)

warmer than the coil sensor (or) the outdoor air sensor indicates

 25_F( 15_C) cooler than the coil sensor, the sensors are out

of range.

S In heating if the outdoor air sensor indicates  35_F( 19.4_C)

warmer than the coil sensor (or) the outdoor air sensor indicates

 10_F( 5.6_C) cooler than the coil sensor, the sensors are out

of range.

If the sensors are out of range, the control will flash the appropriate

fault code as shown in Table 7.

The thermistor comparisons are not performed during low ambient

cooling or defrost operation.

Failed Thermistor Default Operation

Factory defaults have been provided in the event of failure of

outdoor air thermistor (OAT) and/or outdoor coil thermistor

(OCT).

If the OAT sensor should fail, defrost will be initiated based on coil

temperature and time.

If the OCT sensor should fail, defrost will occur at each time

interval during heating operation, but will terminate after 2

minutes.

If there is a thermistor out--of--range error, defrost will occur at

each time interval during heating operation, but will terminate after

2 minutes.

Count the number of short and long flashes to determine the

appropriate flash code. Table 7 gives possible causes and actions

related to each error.

Outdoor Coil Thermistor

The outdoor coil thermistor is a 10Kohm resistor used for multiple

system operations. It provides the coil/liquid line temperature to

the heat pump board and user interface. Low ambient operation,

defrost initiation, defrost termination and assistance with OAT

temperature measurement of some of the functions. The sensor

must be securely mounted to the tube connecting the EXV and

distributor. See Fig. 24 for proper placement. See Table 5 for

proper resistances.

A14302

Fig. 23 -- Outdoor Coil Thermistor (OCT) Attachment

(On Distributor Tube)

OAT Thermistor must be locked in place with

spherical nib end facing towards the front of

the control box

A11142

Fig. 24 -- OAT Thermistor Location (Bottom of Control Box)

1 2 ... 12 13 14 15 16 17 18 19 20 21 22

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