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M
od
Pac II, 9/09-15
The electric heater assembly can have up to three individual heating elements. Each individual
heating element is protected against overheating by its own dual function thermal cut-out switch.
Additionally, a separate single function thermal cut-out switch protects the entire heater assem
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bly.
The dual function thermal cut-out switch (P/N 70006) is composed of two independent line volt
-
age snap-disc temperature switches mounted in a single enclosure. One of these switches is an
automatic reset device which cycles off at approximately 145°F and back on at approximately
115°F. Should this switch fail to open, the second switch will open the circuit if the temperature
continues to increase. This second switch does not reset. If it opens (breaks the line voltage circuit
to the heater assembly) the switch will have to be replaced by qualified service personnel after
the source of the overheat problem is resolved.
In addition to the thermal cut-out switch described above, there is a single function thermal cut-out
switch (P/N 70005) mounted on the heater frame. This switch controls the 24V AC control current
to the heater contactor(s) which powers all the heating elements. This single function thermal cut-
out switch operates totally independent of the dual thermal cut-out switch described above. If the
single function switch senses an overheat situation, it opens the control circuit and turns off all of
the installed heating elements via the heater contactor(s). Because this switch controls the heater
contactor(s), only one switch is required to disconnect power from the contactor(s), regardless of
the number of heater elements. This single function switch is also non-resettable, and must be
replaced by qualified service personnel after the source of the overheat problem is resolved. This
switch would typically open if both elements of the dual thermal cut-out switches failed.
Figure 7. Typical Configuration for Single Element Heater
4.4 Electric Heat Controls