Variable Air Volume Applications (Single Zone Vav); Discharge Air Cool Setpoint Adjustment; Reliatel™ Control Cooling With An Economiz - Trane YSC036G Installation, Operation And Maintenance Manual

Sequence of Operation
be energized for at least 6 minutes to drive all boxes open,
the supply fan is commanded to full speed, and full heat
(gas or electric) is energized. When MWU is activated the
economizer damper is driven fully closed. When the zone
temperature meets or exceeds the MWU setpoint minus
1.5°F, the heat will be turned or staged down. When the
zone temperature meets or exceeds the MWU setpoint
then MWU will be terminated and the unit will switch over
to VAV cooling.
Variable Air Volume Applications
(Single Zone VAV)
Supply Fan Output Control
Units configured for Single Zone VAV will be controlled via
the 0-10 Vdc Indoor Fan Speed output located on the
RTOM. R136 (DA COOL_FAN SPD) potentiometer on the
RTOM sets the maximum motor speed. Note that the
potentiometer voltage readings can be verified via 2-
position harness connector located adjacent to the RTOM.
The unit schematic will illustrate the exact location. Use a
DC voltmeter to read the voltage between the two
terminals. Reference the RPM table in the Performance
Data section for fan speed.
• Use Service TEST Mode to adjust maximum motor
speed using modes listed below.
1. TEST Mode Cool 2; 2-Step Cool applications only
2. TEST Mode Cool 3; 3-Step Cool applications only
• Adjust DA COOL_FAN SPD potentiometer clockwise to
increase or counterclockwise to decrease motor
speed.
• The control will scale the 0-10 Vdc output from the
RTOM linearly to control between the 50%-100%
controllable range based on the space cooling
demand.
Minimum Supply Fan Output
• Refer to the table below for details on minimum supply
fan output signals associated with each unit function.
• Minimum Fan Output%
• Ventilation Only 50%
• Economizer Cooling 65%
• Cool 1 (C1 Energized) 65%
• Cool 2 (C1 + C2) 82% (2-Steps of Cooling)
• Cool 2 (C1 or C2) 65% (3-Steps of Cooling)
• Cool 3 (C1 + C2 Energized) 82%
• Heat 100%

Discharge Air Cool Setpoint Adjustment

• Single Zone VAV units will require traditional zone
heating (if heat installed) and cooling setpoints that are
used on single speed units in addition to a new
setpoint: Discharge Air Cool Setpoint limit. Discharge
56
Air Cool Setpoints will be customer selectable via a
potentiometer (DACR) adjacent to the RTOM with a
range of 40- 70°F.
• The table below lists the discharge air cool setpoints
on the DACR.
Note: The recommended setting is 50°F.
Table 17. Discharge air cool setpoints (DACR)
Setpoint (°F)
40 - <0.1
41 - 0.2
42 - 0.3
43 - 0.45
44 - 0.55
45 - 0.7
46 - 0.8
47 - 0.95
48 - 1.05
49 - 1.15
50 - 1.25
51 - 1.3
52 - 1.35
53 - 1.45
54 - 1.55
70 - >2.4
ReliaTel™ Control Cooling with an
Economizer
The economizer is utilized to control the zone temperature
providing the outside air conditions are suitable. Outside
air is drawn into the unit through modulating dampers.
When cooling is required and economizing is possible, the
RTRM sends the cooling request to the unit economizer
actuator (ECA) to open the economizer damper. The RTRM
tries to cool the zone utilizing the economizer to slightly
below the zone temperature setpoint. If the mixed air
sensor (MAS) senses that the mixed air temperature is
below 53°F, the damper modulates toward the closed
position. If the zone temperature continues to rise above
the zone temperature setpoint controlband and the
economizer damper is full open, the RTRM energizes the
compressor contactor (CC1). If the zone temperature
continues to rise above the zone temperature setpoint
controlband and the economizer damper is fully open, the
RTRM energizes the compressor contactor (CC2).
Multi-Speed Fan
When economizing alone or with 1st stage cooling the
indoor motor will operate at low speed. If economizing
and 2nd stage cooling requested, the indoor motor will
transition from low to high speed.
Single Zone VAV
The indoor motor will vary the indoor motor speed to
optimize minimum fan speed for the cooling demand in all
Voltage (Vdc)
55 - 1.65
56 - 1.7
57 - 1.75
58 - 1.83
59 - 1.9
60 - 1.95
61 - 2
62 - 2.05
63 - 2.1
64 - 2.13
65 - 2.17
66 - 2.21
67 - 2.27
68 - 2.3
69 - 2.35
RT-SVX21AC-EN