Temperature Sensor Checkout; Humidity Sensor Checkout; Suction And Discharge Pressure Transducer Checkout - Carrier 68G5-105 Series Operation & Service Manual

b. Close (frontseat) suction service valve and pump unit
down to 3 to 5 psig (21 to 34 kPa). Reclaim remaining
refrigerant.
NOTE
If oil drain plug is not accessible, it will be
necessary to extract oil through the oil fill plug
with a siphon tube.
WARNING
EXTREME CARE MUST BE TAKEN TO
ENSURE THAT ALL THE REFRIGERANT
HAS BEEN REMOVED FROM THE
COMPRESSOR CRANKCASE OR THE
RESULTANT PRESSURE WILL FORCIBLY
DISCHARGE COMPRESSOR OIL.
c. Remove the oil drain plug on the bottom plate of the
compressor and drain the proper amount of oil from
the compressor. Replace the plug securely back into
the compressor.
d. Repeat step a. to ensure proper oil level.
Table 4-3. Temperature Sensor
(AT, TSC, TSD and TSR) Resistance
Temperature
_F _C
--20 --28.9
--10 --23.3
--17.8
0
10 --12.2
20 -- 6.7
30 -- 1.1
32
0
40 4.4
50 10.0
60 15.6
70 21.1
77 25
80 26.7
90 32.2
100 37.8
110 43.3
120 48.9

4.13 TEMPERATURE SENSOR CHECKOUT

a. An accurate ohmmeter must be used to check
resistance values shown in Table 4-3.
b. Due to variations and inaccuracies in ohmmeters,
thermometers or other test equipment, a reading
within two percent of the chart value would be
considered good. If a sensor is bad, the resistance
value would usually be much higher or lower than the
value given in the Table 4-3.
Resistance In Ohms Resistance In Ohms
165,300
117,800
85,500
62,400
46,300
34,500
32,700
26,200
19,900
15,300
11,900
10,000
9,300
7,300
5,800
4,700
3,800
This system is equipped with three
temperature sensors, two located in the
return air ducts inside the coach, the third
sensor is located in the condenser section.
The two inside sensors are wired in parallel
and together send an averaged signal to the
controller. If one of these sensors fails the
control function will continue with the
remaining sensor. The sensor located in the
condenser section reads outdoor
temperature.

4.14 HUMIDITY SENSOR CHECKOUT

a. Use a sling psychrometer or similar device to check
relative humidity inside the coach.
System can be shut down but 5 vdc power
must be applied to the humidity sensor to
enable checking.
b. Measure voltage across the sensor and compare to
values in Table 4-4 for the measured relative
humidity. A reading within two percent of the values in
the table would be considered good.
c. At least one sensor lead must be disconnected from
the controller before any reading can be taken. Not
doing so will result in a false reading. Two preferred
methods of determining the actual test temperature
at the sensor are an ice bath at 32_F (0_C) and/or a
calibrated digital temperature meter.
d. If the driver display indicates that temperature at
sensor is --40_F (- -40_C), sensor could be open. If
driver display indicates that temperature at sensor is
127_F (52.8_C), sensor could be shorted.
Table 4-4. Humidity Sensor (HS) Voltage
%RH Voltage %RH
30 0.990
35 1.155
40 1.320
45 1.485
50 1.650
4.15 SUCTION AND DISCHARGE PRESSURE
TRANSDUCER CHECKOUT
1. System must be operating to check
transducers.
2. Both transducers are mounted on the
compressor
a. With the system running, use the driver display or
manifold gauges to check suction and/or discharge
pressure(s).
4-11
NOTE
NOTE
Voltage %RH Voltage
55 1.815 80
60 1.980 85
65 2.145 90
70 2.310 95
75 2.475
NOTE
2.640
2.805
2.970
3.168
T-312