Component Troubleshooting; Probe; Relays; Hi Limits - Pitco AG14S Service Manual

COMPONENT TROUBLESHOOTING

Temperature Probe:
The resistance of the probe decreases as the tem-
perature rises. The lower the temperature the greater
the resistance change will be per degree of tempera-
ture change, as the temperature approaches the work-
ing range of the probe, the resistance change will
slow and become more linear. If the probe is sus-
pect, check its resistance and the oil/air temperature
at which it was taken. Compare these values on the
chart below.
TEMP RESISTANCE
Ohms Ω
ºF
139055 Ω
60°
84644 Ω
80°
53146 Ω
100°
34328 Ω
120°
22755 Ω
140°
15446 Ω
160°
10716 Ω
180°
7586 Ω
200°
6427 Ω
210°
5470 Ω
220°
4013 Ω
240°
2991 Ω
260°
2262 Ω
280°
1734 Ω
300°
1347 Ω
320°
1267 Ω
325°
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:

Relays will energize when the correct voltage is sup-
TEMP RESISTANCE
Ohms Ω
ºF
1192 Ω
330°
1123 Ω
335°
1058 Ω
340°
998 Ω
345°
942 Ω
350°
890 Ω
355°
841 Ω
360°
795 Ω
365°
752 Ω
370°
712 Ω
375°
675 Ω
380°
640 Ω
385°
607 Ω
390°
576 Ω
395°
547 Ω
400°
plied to the coil. When energizing, the relay Switch-
ing Contacts will close, thus connecting the Com-
mon and Normally Open terminals.

Hi Limits:

A Hi - Limit switch is a normally closed switch until
the temperature at its probe reaches 435ºF ± 15°
(225ºC ± 15º). In order to test this switch it will be
necessary to bypass the Heat Demand Relay.
This will cause the fryer to heat until the tem-
perature of the oil reaches the necessary tem-
perature to trip the Hi Limit.
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. Always use an external
temperature probe to observe the oil tempersature
during this procedure
In order to cause the oil to reach a temperature where
the Hi Limit will trip it will be necessary to bypass
the Heat Demand Relay. To do this, use a small
jumper wire and join the Normally Open (Terminal
#5) and Common (Terminal #3) terminals on the
switch section of the relay
If the switch does not trip between the prescribed
limits it is defective and should be replaced. Once
tripped, the switch cannot be reset until the oil
has cooled to approximately 400°F (204ºC). If
the switch cannot be reset it is defective.
Drain Valve & Return Valve Switches:
These switches are magnetically operated Reed
switches. 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
6 mm).
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