RTHD and RTAC - Trane

External LLID Sensor
Internal LLID
The liquid level sensor is mounted in a small tank or canister attached to the
outside of the tube sheet. The evaporator’s liquid level is transmitted into the
tank through a small vapor and liquid line.
The liquid level sensor is required to provide input for control of the EXV, which
allows the regulation of refrigerant flow into the evaporator, to match the
compressor capacity. This provides for increased part load efficiencies compared
to a fixed orifice device.
There are two types of sensors that are used on RTAC and RTHD units. A float
type senor with an external LLID was originally used on RTAC and RTHD units. A
capacitance based with an internal LLID will soon be used on all units.
The sensor consists of a body made from an enclosed tube and fitting, and a
magnetic float which slides over the tube. Internal to the tube, and isolated from
the refrigerant, is a narrow PC board with a resistor and magnetic reed switch
array. The float's magnets close the reed switches pattern as it moves up the
tube, creating a changing resistance (and ultimately a direct acting DC output
voltage) similar to that of a potentiometer
This new level sensor is a capacitive based switch. This switch is more reliable
and has no moving parts. It is less sensitive to foam and will provide consistent
operation across the operating map.This new sensor can be installed on existing
chillers using an adapter.
There are 2 capacitor sensors in the copper tube. The lower sensor is used to
determine the capacitance of the liquid (refrigerant and oil mixture). The upper
sensor is used to determine the height of the liquid in the evaporator.
Liquid Level Sensor Checkout Procedure
Is the sensor
bound and
communicating?
Liquid Level Sensor
Connect TechView and get into Binding View. This will shut the chiller down.
Once in Binding View verify that the Liquid Level Senor is bound.
Note: Please refer to Service Tool for questions concerning binding LLIDs and
getting into Binding View.
If there are multiple LLIDs that are not verified go to IPC troubleshooting.
If the sensor is not bound, try to bind it. If the sensor will not bind, it could be a
problem with the connector or the sensor itself. Take a close look at the
connector to make sure that all four wires are securely in place. It may be
necessary to remove the cap to check for broken or misplaced wires.
RLC-SVD05A-EN 57