Pitco MG14S-C/MFD, Руководство по обслуживанию, Страница: 9 / 39

5
Chapter 2: COMPONENT
TROUBLESHOOTING:
Probe:
The resistance of the probe will change as the tem-
perature changes. The resistance will decrease as the
temperature rises. The lower the temperature the
greater the resistance change will be per degree of
temperature change, as the temperature approaches
the working range of the probe, the resistance change
will become more linear.
If the probe is suspect, check its resistance and the
oil/air temperature at which it was taken. Compare
these values on the chart below.
TEMP RESISTANCE TEMP RESISTANCE
ºF Ohms ºF Ohms
60 139055 330 1192
80 84644 335 1123
100 53146 340 1058
120 34328 345 998
140 22755 350 942
160 15446 355 890
180 10716 360 841
200 7586 365 795
210 6427 370 752
220 5470 375 712
240 4013 380 675
260 2991 385 640
280 2262 390 607
300 1734 395 576
320 1347 400 547
325 1267
If the probe returns an open circuit or 0 Ohms read-
ing it should be replaced. If the resistance varies more
than 20 Ohms from the above chart when being
checked between 325-375°F (162ºC - 190ºC) the
probe will give a false temperature reading on the
computer and should be replaced. However, it will
continue to operate at a slightly higher or lower tem-
perature. Allow the oil to cool and check the probe
resistance at a lower temperature. As can be seen
from the chart a greater degree of offset can be al-
lowed at a lower temperature.
Relays:
The Heat Demand and Hood relays are 24VDC re-
lays and will energize when the correct voltage is
supplied to the coil. When energizing, the relay
Switching Contacts will close, thus connecting the
Common and Normally Open terminals. The Hi -
Limit relay is a 24VAC relay and may be checked in
the same manner as the above relay.
Hi Limits:
A Hi - Limit switch is a normally closed switch until
the temperature at the probe reaches 435ºF ± 15°
(225ºC ± 15º). In order to test this switch it will be
necessary to bypass the Heat Demand Relay. Follow
the Hi Limit testing proceedure outlined on page 8
of the Operating Manual.
WARNING
Do NOT leave the machine during this test. This
test will cause the oil to heat past the normal oper-
ating temperature and can cause damage to the
machine and its operator.
If the switch does not trip between the prescribed
limits it is defective and should be replaced. Once
tripped, the switch will not reset until the oil has
cooled to approximately 400°F (204ºC). If the switch
does not reset it is defective.
Drain Valve & Return Valve Switches:
This switch is a magnetically operated Reed switch.
When the Drain Valve handle is moved to the open
position, the Actuator will move away from the
switch causing the Reed switch to open. When the
Drain Valve is closed the Reed switch will close.
This switch can also be checked with an Ohm meter.
The normal gap between the Actuator and the Sen-
sor switch on the Drain Valve handle is
1
/
8
" -
1
/
4
" (3 -
6 mm).