RT-SVX34C-EN 11 3
Sequence of Operation
Units without an Economizer
For 27.5 to 35 Ton units, when mechanical cooling is required, the RTRM energizes the Compressor
Contactor (CC1) coil. When the CC1 contacts close, the Compressor CPR1 and Outdoor Fan Motor
(ODM1) will start providing the 3 minute "off" time has elapsed. ODM2 and ODM3 cycles off/on
based on the outdoor ambient temperature as measured by the Outdoor Air Sensor (OAS). CPR1
cycles off as required providing the 3 minute "on" time has elapsed.
With CPR1 operating for a minimum of 3 minutes. If additional cooling is required, the RTRM
energizes the 2nd compressor contactor (CC2) to bring on CPR2. While CPR1 continues to run, CPR2
cycles on/off as needed to meet the cooling requirements.
For 40 Ton constant volume and variable air volume applications, once CPR1 has operated for a
minimum of 3 minutes, and additional cooling is required, the RTRM cycles CPR1 off and energizes
compressor contactor CC2. If additional cooling is required, the RTRM energizes compressor
contactor (CC1) providing CPR1 has been off for a minimum of 3 minutes. This configuration will
allow the dual circuit unit to operate with three steps of cooling if CPR1 is the lead compressor.
For 50 Ton constant volume and variable air volume applications, once CPR1 has operated for a
minimum of 3 minutes, and additional cooling is required, the RTRM cycles CPR1 off and energizes
compressor contactors CC2 and CC3 simultaneously. If additional cooling is required, the RTRM
energizes compressor contactor (CC1) providing CPR1 has been off for a minimum of 3 minutes.
This configuration allow the dual circuit unit to operate with three steps of cooling if CPR1 is the
lead compressor.
If the indoor Fan selection switch is set to the “AUTO” position on constant volume applications,
the RTRM energizes the Indoor Fan Contactor (F) coil approximately one second after energizing
first stage compressor contactor (CC1). When the cooling cycle is complete and CC1 is de-
energized, the RTRM keeps the Fan on for approximately 60 seconds to enhance unit efficiency. On
variable air volume applications, the Fan operates continuously.
Economizer operation based on Dry Bulb
Standard economizer dry bulb change over has five field selectable temperatures 55, 63, 67, 70, 73°
F. Refer to Table 22, p. 64 for the proper potentiometer setting for each temperature selection.
The economizer option allows cooling utilizing outdoor air when the temperature is below the
specified dry bulb setpoint (73° ±2° F factory setting). The air is drawn into the unit through
modulating dampers. The ECA modulates the economizer dampers from minimum position to full
open based on a 1.5° F control point below either the space temperature setpoint for constant
volume applications or 1.5° F around the supply air temperature setpoint for variable air volume
applications.
If the Mixed Supply Air Sensor (MAS) senses that supply air temperature is too cold, the dampers
are held in their current position until the supply air temperature rises, or begin to modulate toward
the minimum position if the supply air temperature continues to drop.
The economizer control allows fully integrated cooling operation between the compressor(s) and
the economizer when needed to satisfy the cooling setpoint. The RTRM will not allow a compressor
to operate until the economizer dampers have been fully open for at least three minutes. The RTRM
evaluates the rate of temperature change during this delay and will energize compressor(s) as
needed to maintain temperatures within setpoint deadbands.
If a power exhaust option is installed:
1. The power exhaust fan(s) comes on based on the position of the of the exhaust fan setpoint
potentiometer on the RTOM (Reliatel Options Module). The setpoint is factory set at 25%. The
exhaust fan(s) will come on anytime the economizer damper position is equal to or greater than
the exhaust fan setpoint.
2. Physical damper blade "stops" that limit the amount of exhaust airflow by limiting the
maximum opening of the damper blades. These stops (sliding brackets secured with wing-
nuts) are present under the rain hood on the non-modulating power exhaust option. There is
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