Carrier 040-420 User Manual

Page 60

Thermistors

All thermistors are identical in their tem-

perature vs. resistance performance. Resistance at various
temperatures are listed in Tables 15 and 16.

LOCATION General location of thermistor sensors are
shown in Fig. 13.

Cooler Leaving Water Thermistor

is located in

leaving water nozzle. The probe is immersed directly in the

All thermistor connections are made through a

coupling. See Fig. 15. Actual location is shown in Fig. 13

and 14.

Cooler Entering Water Thermistor

T2 is located in

cooler shell in first baffle space near tube bundle. Ther-

mistor connection is made through a

coupling. See

Fig. 15. Actual location is shown in Fig. 13 and 14.

Compressor Suction Gas Temperature Thermistors

and

T7 and

are located in lead compressor in each

circuit in suction passage between motor and cylinders, above
oil pump. They are well-type thermistors on 040-210 and
associated modular units, or ferrule-type on 225, 250, 280
units. See Fig. 13 and 14.

THERMISTOR REPLACEMENT (Tl , T2, T7,

(Com-

pressor and Cooler)

Thermistors are installed directly in fluid or refrigerant
circuit. Relieve all refrigerant pressure using standard
refrigerant practices or drain fluid before removing.

Proceed as follows (see Fig. 15):
To replace sensors

T2, T7

and

1. Remove and discard original thermistor and coupling.

IMPORTANT: Do not disassemble new coupling.
Install as received.

2. Apply pipe sealant to

NPT threads on replace-

ment coupling and install in place of original. Do not
use packing nut to tighten coupling. This damages fer-
rules (see Fig. 15).

3. Insert new thermistor in coupling body to its full depth.

If thermistor bottoms out before full depth is reached,
pull thermistor back out in, before tightening packing

nut. Hand tighten packing nut to position ferrules, then
finish tightening

turns with a suitable tool. Ferrules

are now attached to thermistor which can be withdrawn

from coupling for unit servicing.

To replace thermistors T7 and (040-210 and associated

modular units):

Add a small amount of thermal conductive grease to ther-
mistor well. Thermistors are friction-fit thermistors, which
must be slipped into receiver located in the compressor pump
end.

Pressure Transducers

of pressure trans-

ducers are used on 30G

a low pres-

sure transducer and a high pressure transducer. The low
pressure transducer is identified by a white dot on the body
of the transducer, and the high pressure transducer by a red
dot. See Fig. 16.

Three pressure transducers are mounted on each lead com-

pressor: 2 low-pressure transducers to monitor compressor

suction pressure and oil pressure, and a high-pressure trans-
ducer to monitor compressor discharge pressure (see

Fig. 17 for exact locations on compressor). Each transducer
is supplied with 5 vdc power from a rectifier which changes
24

to 5 vdc.

TROUBLESHOOTING

If transducer is suspected of be-

ing faulty, first check supply voltage to transducer. Supply
voltage should be 5 vdc v. If supply voltage is cor-

rect, compare pressure reading displayed on keypad and dis-

play module against pressure shown on a calibrated pres-
sure gage. If the 2 pressure readings are not reasonably close,

replace pressure transducer.

TRANSDUCER REPLACEMENT

Transducers are installed directly in the refrigerant cir-

cuit. Relieve all refrigerant pressure using standard re-
frigeration practices before removing.

1. Relieve refrigerant pressure using standard refrigeration

practices.

2. Disconnect transducer wiring at transducer by pulling

up on locking tab while pulling weather-tight connection

pfug from end of transducer. Do not pull on trans-

ducer wires.

3. Unscrew transducer from

male flare fitting. When

installing new pressure transducer, do not use thread
sealer. Thread sealer can plug transducer and render it
inoperative.

4. Insert weathertight wiring plug into end of transducer

until locking tab snaps in place.

5. Check for refrigerant leaks.

SAE FEMALE FLARE

WHITE DOT-LOW PRESSURE TRANSDUCER
RED DOT -HIGH PRESSURE TRANSDUCER

SAE

Society of Automotive Engineers

Fig. 16

Pressure Transducer