Section 18 - Temperature Thermistors - York MAXE OPTIVIEW YK Service Instructions Manual

Temperature Thermistors
System temperatures are sensed by Thermistors. There
are two different thermistor types used to sense the var-
i ous system temperatures. Each type has its own YORK
part number. Part numbers are listed in YORK Re new al
Parts List 160.54-RP2. The Return and Leav ing Chilled
Liquid, Return and Leaving Condenser Liq uid, Drop Leg
Re frig er ant and Evaporator Tem per a tures are sensed by
3K Ohm thermistors. The Oil and Com pres sor Discharge
tem per a tures are sensed by 50K Ohm thermistors.
The 3K Ohm thermistors are defi ned by the char ac -
ter is tic of being 3000 Ohms at 77ºF (25ºC). Similarly,
the 50K Ohm thermistors are 50,000 Ohms at the same
tem per a ture. Both thermistor types vary their resistance
as the sensed temperature varies. Both are negative tem-
per a ture coeffi cient devices. That is, as the tem per a ture
increases, the resistance decreases. As the tem per a ture
decreases, the resistance increases.
The thermistors are connected to the Microboard. A
+5VDC supply voltage is applied to one side of the
ther mistor. The other side of the thermistor is connected
to Ground through a series resistor on the Microboard,
thus forming a voltage divider network. The tem per a ture
ap plied to the thermistor determines the resistance value.
The resistance value determines the amount of current that
102
SECTION 18
TEMPERATURE THERMISTORS
(REFER TO FIG. 58 - 63)
will fl ow through the thermistor and thus the voltage drop
across it. The Program reads this volt age at the input to the
Microboard and converts it to a temperature value.
Each thermistor is connected to the Microboard with two
wires. One wire supplies the +5VDC voltage and the oth er
is the output of the thermistor. This output volt age can be
measured with a Voltmeter. Mea sure ment should be made
from the thermistor output to Ground (Gnd). For ex am ple,
the Leaving Chilled Liq uid Tem per a ture would be read
from Microboard J9-20 (output) to Microboard TP1 (Gnd).
To convert this voltage to a pressure, refer to the ap pro pri ate
volts/temp chart as fol lows:
• Leaving Chilled Liquid Temperature – Fig. 58
• Return Chilled Liquid Temperature – Fig. 59
• Leaving and Return Condenser Liquid Tem per a ture
– Fig. 60
• Oil and Discharge Temperature – Fig. 61
• Drop Leg Refrigerant Temperature – Fig. 62
• Evaporator Refrigerant Temperature – Fig. 63
If any of the displayed pressures do not appear to be
correct, refer to the "Diagnostics and Trou ble shoot ing"
section of this book.
FORM 160.54-M1(503)
YORK INTERNATIONAL