Carrier Air Conditioner specifications Thermistors Temperature Sensors

Thermistors — Electronic control uses 4 to 10 ther- mistors to sense temperatures used to control the operation of chiller.

Thermistors T1-T9 vary in their temperature vs resistance and voltage drop performance. Thermistor T10 is a 10 kΩ in- put channel and has a different set of temperature vs resistance and voltage drop performance. Resistances at various tempera- tures are listed in Tables 32A-33B.

LOCATION — General locations of thermistor sensors are shown in Fig. 7-10. See Table 2 for pin connection points.

Sensor T2 is installed directly in the fluid circuit. Relieve all pressure or drain fluid before removing.

REPLACING THERMISTOR T2

1. Remove and discard original sensor and coupling. Do

not disassemble new coupling. Install assembly as

received. See Fig. 32.

Tables 32A-33B. To check thermistor accuracy, mea- sure temperature at probe location with an accurate thermocouple-type temperature measuring instru- ment. Insulate thermocouple to avoid ambient temper- atures from influencing reading. Temperature measured by thermocouple and temperature deter- mined from thermistor voltage reading should be close, ± 5° F (3° C) if care was taken in applying ther- mocouple and taking readings.

2.If a more accurate check is required, unit must be shut down and thermistor removed and checked at a known temperature (freezing point or boiling point of water) us- ing either voltage drop measured across thermistor at the J8 or J5 terminals, by determining the resistance with chiller shut down and thermistor disconnected from J8 or J5. Compare the values determined with the value read by the control in the Temperatures mode using the Marquee display.

2. Apply pipe sealant to 1/4-in. NPT threads on replacement

coupling, and install in place of original. Do not use the

packing nut to tighten coupling. Damage to ferrules will

result.

3. Thermistor T2 (entering fluid temperature) should not be

touching an internal refrigerant tube, but should be close

enough to sense a freeze condition. Recommended dis-

tance is 1/8 in. (3.2 mm) from cooler tube. Tighten pack-

ing nut finger tight to position ferrules, then tighten 11/4

turns more using a back-up wrench. Ferrules are now at-

tached to the sensor, which can be withdrawn from cou-

pling for service.

REPLACING THERMISTORS T1, T5, T6, T7, AND T8 — Add a small amount of thermal conductive grease to thermistor well. Thermistors are friction-fit thermistors, which must be slipped into wells located in the cooler leaving fluid nozzle for T1, in the cooler head for T5 and T6 (EXV units only), and in the compressor pump end for T7 and T8 (EXV units only).

THERMISTORS T3 AND T4 — These thermistors are located on header end of condenser coil. They are clamped on a return bend.

THERMISTOR/TEMPERATURE SENSOR CHECK — A high quality digital volt-ohmmeter is required to perform this check.

1.Connect the digital voltmeter across the appropriate thermistor terminals at the J8 terminal strip on the Main Base Board for thermistors T1-T6, T9, T10; or the J5 terminal strip on the EXV Board for thermistors T7 and T8 (see Fig. 33). Using the voltage reading

obtained, read the sensor temperature from

MAIN BASE BOARD

	1	1
	2	2
	3	3
	4	4
	5	5	BLU TB5		5
	6	6	BLU TB5		6
	7	7	PNK TB5 7
	8	8	PNK	TB5	8
	9	9
	10	10
				T2
	11	1	2
	12	2
J8	13	3	1	T1
	14	4
	15	1	4	T4
	16	2
	17	3
				T6
	18	4	6
	19	5
	20	6
				T3
	21	1	3

222

233

24 4 5 T5

25	5
26	6

REMOTE SPACE TEMP

(ACCESSORY)

T10

T9

OUTDOOR-AIR TEMP

(ACCESSORY) OR DUAL CHILLER LWT

COOLER ENTERING FLUID TEMP

COOLER LEAVING FLUID TEMP

SATURATED CONDENSING TEMP- CIRCUIT B

SATURATED

SUCTION TEMP-

CIRCUIT B*

SATURATED CONDENSING TEMP- CIRCUIT A

SATURATED

SUCTION TEMP-

CIRCUIT A*

X = T1,T5,T6 = 3″ (76)

T7,T8 = 4″ (102)

FLUID-SIDE TEMPERATURE SENSOR (T1) AND

REFRIGERANT TEMPERATURE SENSOR (T5, T6, T7, T8)

FLUID-SIDE TEMPERATURE SENSOR (T2) NOTE: Dimensions in ( ) are in millimeters.

Fig. 32 — Thermistors (Temperature Sensors)

T1-T6, T9, T10 THERMISTORS

EXV BOARD

J5

12 11 10 9 8 7 6 5 4 3 2 1

12 11 10 9

T7 7 8 T8

CKTA* CKTB*

COMPRESSOR RETURN GAS TEMP

T7, T8 THERMISTORS

LEGEND

LWT — Leaving Fluid Temperature

*Not used on units with TXV (Thermostatic Expansion Valve) FIOP (Factory-Installed Option).

Fig. 33 — Thermistor Connections to J5 and J8

Processor Boards

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