Trane RT-SVX10C-EN Electric Heat Sequence of Operation, Wet Heat Sequence of Operation

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-K1energizes. 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.

Unit Start-Up (Continued)

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-K3energizes. 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

40F, 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.

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