Electric Heat Sequence Of Operation; Wet Heat Sequence Of Operation - Trane IntelliPak Installation, Operation And Maintenance Manual

If the pilot is ignited within 10 seconds, the IC board de-
energizes the ignition transformer 4T7 and electrode 4E1.
At this point, relay 4K119 will energize, starting the
combustion air actuator and the furnace.The feedback
signal from the discharge temperature sensor will cause
the modulating output from the heat module to change the
damper position as required to maintain the outlet
temperature within the desired band.
Flame Failure
In the event that IC board 4U18 loses the "proof-of-flame"
input signal during furnace operation, it will make one
attempt at reignite. If a flame is not reestablished within
the 10 second trial period, 4U18 will shut down and lock
out the ignition /combustion control circuit. (Combustion
blower motor 4B11 continues to run as long as a heating
requirement exists and control circuit switch 4S24 is ON.)
Once locked out on flame failure, the IC board will not
reactivate the ignition/combustion control circuit until it is
reset manually.To do this, press the reset button on the
front of the IC board case.
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 operation. 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.
• High limit Switch 4S27 will trip if exposed to a
temperature of 133 + 5°F , and reset automatically once
the temperature falls to 110 + 5°F . It is mounted on the
control-box-side of the electric heat element assembly.
• Linear high limit 4S33 is encased in a capillary that
extends across the unit's supply air opening, and is
anchored 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 67, p. 163The HEAT 2 (4K36, 4K37) and HEAT 3
(4K38, 4K39) contactors are not energized unless the
1st stage bank of heating elements already operating
are not satisfying the heating load.
RT-SVX36K-EN

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 2 VDC and fully open (10 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,
completing 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 67, p. 163.
Use the checklist provided below in conjunction with the
"General Unit Requirement" checklist to ensure that the
unit is properly installed and ready for operation. Be sure
to complete all of the procedures described in this section
before starting the unit for the first time.
• Turn the field supplied disconnect switch, located
upstream of the rooftop unit, to the "Off" position.
WARNING
Hazardous Voltage!
Disconnect all electric power, including remote
disconnects before servicing. Follow proper lockout/
tagout procedures to ensure the power can not be
inadvertently energized. Failure to disconnect power
before servicing could result in death or serious injury.
• Turn the 115 volt control circuit switch 1S1 to the "Off"
position. It is located in the secondary of the 1T1
transformer.
• Turn the 24 volt control circuit switch 1S70 to the "Off"
position. It is located in the secondary of the 1T2 & 1T3
transformers.
Unit Start Up
93