Temperature Sensors

Thermistor type temperature sensors are used. Each sensor is connected to a cable and placed in a sealed stainless steel tube. The temperature signal from the sensor is transmitted through the cable. Temperature sensors include the following:

  • Supply Air

  • Return Air

  • Evaporator Coil

  • Condenser Coil

  • Compressor Discharge Temperature Sensor

  • Ambient Air

      
     
  1 Temperature Sensors
     
     
     
     
Parent topic: Electrical Maintenance

Sensor Installation

All sensors should be properly installed as follows:

  • Supply air sensors must be inserted to the bottom of the sensor tube and completely sealed by the grommet connection.

  • Return air sensor installs in a grommet between the evaporator fans.

  • Evaporator coil (defrost) sensor must be placed in the middle of the coil and 75 mm deep between the fins.

  • Condenser sensor must be placed on the upper left side of the condenser coil and 70 mm deep between the fins.

  • Ambient sensor must be placed on the bottom plate of the right forklift pocket.

  • Compressor discharge temperature sensor is attached to compressor head by adhesive. Refer to (Compressor Discharge Temperature Sensor).

Sensor Testing

The controller constantly monitors the left hand and right hand supply sensors, return sensor and defrost (evaporator coil) sensor to determine when to initiate a demand defrost. If a demand defrost is requested and defrost has occurred within the last 90 minutes, the controller initiates a probe test to check for a defective sensor.

During a Probe test, the VGA display shows [PROBE TEST PLEASE WAIT]. The controller operates the unit on high speed evaporator fans only for five minutes. All sensor temperatures are then compared.

  • Sensors with large temperature differences are discarded from the control algorithm. The controller then activates the appropriate Alarm codes to identify the defective sensor(s).

Sensor errors recorded during a probe test are cleared when the next Defrost is initiated or Unit On/Off switch is turned Off.

Note A manual probe test can be performed by a technician by selecting “SENSOR CHECK” from the Manual Test Function menu.
Evaporator Coil (Defrost) Sensor Location
      
  A Coil Support Bracket
  B Front of Unit
  C Insert sensor at least 75 mm into coil between tube rows 2 and 3.
     
     
     
     
Condenser Coil Sensor Location
      
  A Insert sensor into condenser coil between tube Rows 1 and 2.
     
     
     
     
     
     

Resistance Values for Temperature Sensors

Sensors are permanently calibrated and can be checked using an ohmmeter. Ohm readings should agree with the data shown in the following sensor resistance tables.

Supply, Return, Evaporator Coil, Condenser Coil, and Ambient Air Sensors

°F °C Ohms °F °C Ohms
-40 -40 842,9 53.6 12 1046,8
-31 -35 862,5 57.2 14 1054,6
-22 -30 822,2 60.8 16 1062,4
-13 -25 901,9 64.4 18 1070,2
-4 -20 921,6 68 20 1077,9
5 -15 941,2 71.6 22 1085,7
10.4 -12 956,9 75.2 24 1093,5
14 -10 960,9 78.8 26 1101,2
17.6 -8 968,7 82.4 28 1109,2
21.2 -6 976,5 86 30 1116,7
24.8 -4 984,4 89.6 32 1124,5
28.4 -2 992,2 93.2 34 1132,2
32 0 1000,0 96.8 36 1139,9
35.6 2 1007,8 100.4 38 1147,7
39.2 4 1015,6 104 40 1155,4
42.8 6 1023,4 107.6 42 1163,1
46.4 8 1031,2 111.2 44 1170,8
50 10 1039,0 113 45 1174,7

Compressor Discharge Sensors

°F °C Ohms °F °C Ohms
-13 -25 1,121,457 185 85 9,202
-4 -20 834,716 194 90 7,869
5 -15 627,284 203 95 6,768
14 -10 475,743 212 100 5,848
23 -5 363,986 221 105 5,091
32 0 280,824 230 110 4,446
41 5 218,406 239 115 3,870
50 10 171,166 248 120 3,354
59 15 135,140 257 125 2,924
68 20 107,440 266 130 2,580
77 25 86,000 275 135 2,279
86 30 69,282 284 140 2,021
95 35 56,158 293 145 1,797
104 40 45,812 302 150 1,591
113 45 37,582 311 155 1,393
122 50 30,986 320 160 1,247
131 55 25,680 329 165 1,118
140 60 21,397 338 170 1,015
149 65 17,914 347 175 920
158 70 15,067 356 180 834
167 75 12,728 365 185 748
176 80 10,793 374 190 679