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Startup

RT-SVX34F-EN

Power Exhaust Control (Tracking)

The power exhaust dampers proportionally track or follow
the fresh air (economizer) damper position. The offset
between the fresh air and the exhaust damper(s) is
adjustable, see figures beginning with

Figure 51, p. 73

Refer to Power Exhaust Fan Performance” tables
beginning with

Table 49, p. 73

Lead/Lag Control

Lead/Lag is a selectable input located on the RTRM. The
RTRM is configured from the factory with the Lead/Lag
control disabled. To activate the Lead/Lag function, simply
remove the jumper connection J3-8 at the RTRM Lead/Lag
input. When it is activated, each time the designated lead
compressor(s) is shut off due to the load being satisfied,
the lead compressor or refrigeration circuit switches.
When the RTRM is powered up, i.e. after a power failure,
the control will default to the number one compressor.

Coil Frost Protection

The Frostat™ control monitors the suction line
temperature to prevent the evaporator from freezing due
to low operating temperatures whenever there is a
demand for cooling. When a closed circuit has occurred for
5 seconds minimum, the RTRM turns off all of the cooling
outputs. The Supply Fan will be held “On” until the Frostat
has been open for 5 continuous seconds or for 60 seconds
after the last compressor was shut “Off”, whichever is the
longest. The compressor shutdown is communicated to
Tracer, if applicable. There is no local diagnostic for this
condition.

Dehumidification Frost Protection

Two control schemes will be active on units configured for
Dehumidification. The first employs the use of the Frostat
function. The second scheme takes precedence over
Frostat. Operation will be as described below.

The second scheme is in control during active
dehumidification or cooling and includes the use of an
Entering Evaporator Temperature sensor (EET). If the EET
drops below 35°F for 10 continuous minutes compressors
will stage off. For dual circuit units one circuit will be
staged off initially, and then if the EET remains below 35ºF
for an additional 10 minutes, the second circuit will be
staged off. For single circuit units one compressor will be
staged off initially, and then if the EET remains below 35ºF
for an additional 10 minutes, the second circuit will be
staged off. When the unit is operating in dehumidification
mode, only the reheat circuit will be re-enabled if the EET
rises above 45ºF. The cooling circuit will not be re-enabled
during dehumidification until the unit leaves the current
dehumidification cycle or a dehumidification purge is
initiated. If the unit is operating in Cooling, the first circuit
that de-energized will be re-enabled when the EET rises
above 45ºF. The second compressor will be allowed to re-
energize at 10 minutes after the EET rises above 45ºF or if
a purge cycle is initiated.

VFD Programming Parameters

See System Troubleshooting section.

Condenser Fan Sequencing Control

The condenser fans are cycled according to the outdoor air
temperature and the number of cooling steps that are
operating.

Table 28

lists the temperatures at which the A

and B Condenser Fan Outputs on the RTRM switches the
fans “Off”. The fans are switched back “ON” when the
outdoor temperature rises approximately 5° F above the
“Off” temperature.

Figure 46, p. 53

shows the condenser fans as viewed from

the top of the unit facing the control panel. Whenever a
condenser fan is cycled back “On”, the condenser fan
Outputs A and B and the compressor steps are de-
energized for approximately seven seconds to prevent
problems with fan windmill.

Figure 45.

Transducer voltage output vs. pressure input for
building pressure

Table 27.

Capacity steps with lead/lag enabled

Unit Size

Step 1

Step 2 Step 3

TC*330

LEAD

48%

100%

LAG