Trane INTELLIPAK ™ ™ ™ ™ ™ Commercial Single-Zone Rooftop Air Conditioners with CV or VAV Control - Manual (Page 60)

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Unit Start-Up (Continued)
A set of relay contacts are available for external use for
heat fail (Information Only).
Note: The modulating gas heaters are factory
adjusted for the proper air/gas ratio at minimum
and nameplate rated firing MBH for most areas in
the country.
Electric Heat Sequence of Operation
The control system for the rooftop units are wired to ensure
that the heating and cooling do not occur simultaneously.
Refer to the electric heat wiring diagrams that shipped with
the unit while reviewing the following sequence of opera-
tion. As you review the sequence of operations, remember
these points:
Whenever there is a call for heat, 1U50-K1 energizes. This
energizes HEAT 1 contactors 4K34 and 4K35 which, in
turn, energize two of the six 4HR3 heating elements.
Note: Electric heater 4HR3 will only energize if both
of the heat section’s high limit safety controls—
4S27 and 4S33—are closed.
1. High limit Switch 4S27 will trip if exposed to a tempera-
ture of 133 + 5 F, and reset automatically once the tem-
perature falls to 110 + 5 F. It is mounted on the control-
box-side of the electric heat element assembly.
2. Linear high limit 4S33 is encased in a capillary that ex-
tends across the unit’s supply air opening, and is an-
chored near the bottom of the heat section control box.
It is designed to trip if the temperature across any 6"
span of the capillary exceeds 185 + 10 F. Refer to
Table 5-1.
The HEAT 2 (4K36, 4K37) and HEAT 3 (4K38, 4K39) con-
tactors are not energized unless the 1st stage bank of heat-
ing elements already operating are not satisfying the heat-
ing load.
Wet Heat Sequence of Operation
Electrical circuitry for units with steam or hot water heat is
limited to the connections associated with the modulating
valve actuator (4U15) and the freezestat (4S12).
Like the furnaces described earlier, SL/SH control systems
are wired to ensure that simultaneous heating and cooling
do not occur. The supply fan will cycle "On" and "Off" with
each call for heat during both an occupied and unoccupied
period.
Whenever there is a call for heat, 1U50-K3 energizes. This
allows a modulated voltage signal to be sent to the “Wet”
heat actuator 4U15. Depending on the value of this signal,
4U15 regulates the flow of steam or hot water through the
coil by positioning the valve stem at some point between
fully closed (6 VDC) and fully open (8.5 VDC).
Freeze Protection
A freezestat (4S12) is mounted inside the heat section of
SLH_ and SSH_ units to prevent the “wet” heat coil from
freezing during the "Off" cycle.
If the temperature of the air leaving the heating coils falls to
40 F, the freezestat's normally-open contacts close, com-
pleting the heat fail circuit on the UCM. When this occurs:
a. The supply fan is turned "Off".
b. "Wet” heat actuator 4U15 fully opens to allow hot
water or steam to pass through the heating coil and
prevent freeze-up.
c. A "Heat Fail" diagnostic is displayed on the Human
Interface LCD screen.
For heating control settings and time delay specifications,
refer to Table 5-1.