McQuay AGS 206A Operation Manual Download

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AGSB-5

Slide Calibration Procedure

The slide is calibrated in the factory before shipment but may have to be recalibrated in the
field, especially if relevant slide parts have been replaced.

Slide Position is a relative capacity adjustment from 0.0%(Min load) to 100.0%(Max Load).
There are two MicroTech II controller readings that apply to the indicator, Slide Target and
Slide Position. It is important to understand the difference between these. The

Slide Target

is the value in which the controller uses to display the calculated prediction of slide
position. This value represents the destination or goal of pulsing the load and unload
solenoids. The slide target is used for direction of control for all load and unload operations,
including alarm limit events. When putting a circuit in Manual mode, the slide target is the
value that you will be adjusting and the controller will load or unload the chiller to match,
with in about 3%, the target entered with the current slide position value. The second value
is the

Slide Position (Pos)

this is the slide position value which is the 4-20mA reading

received from the position indicator. These values can be viewed at the circuit controller on
screen “VIEW CIR STATUS (1)”.

A slide target of 0.0% is fully unloaded and the unload solenoid will be constantly
energized. A slide target of 100.0% means that the chiller is at full load and the load
solenoid is continually energized. The chiller will regulate the slide position to infinite steps
between 0% and 100% by pulsing the appropriate solenoid. Facing the front of the
compressor the solenoid on the left is for load (oil vent) and the solenoid on the right is for
unload (oil feed). In Circuit Enable mode (normal operation) the controller makes decisions
to move the Slide target, the calculated value, and pulses the proper solenoid in order to
keep the actual and the target position with in a few percent.

1. It is recommended that the circuit to be calibrated is near normal operating

temperatures, although a preliminary calibration before first starting the compressor is
acceptable, as long as the value is verified soon after compressor shuts down. Note that
it requires sufficient oil pressure to unload the compressor while it is running, and may
load up due to lack of oil pressure. When the compressor is not running there is a large
spring that forces the compressor unloaded, therefore in the off state you have the best
opportunity for verifying an accurate calibration at minimum slide position.

2. On the Circuit controller first verify what your current slide target is at screen “View

Circ Status (1)” and then go to screen “SET COMP SPs (2)” to switch circuit into
manual slide control. Note: Some inhibit limits will be ignored but all alarm limits are
still active.

3. Slowly take the circuit either to 0% or 100% load. When the slide target is at either 0%

or 100%, you may want to verify that the corresponding coil is energized.

4. On the circuit controller scroll all the way to the right, then the calibration and offsets

menu. Scroll down until you see “SET SENSOR OFFSET (3)”. You will see an
adjustment for Min Load and Max Load and on the bottom line you will see the value of
the actual slide position indicator. Add offset until value is /-.5%.

5. Repeat until all circuits have both positions calibrated with in +/-.5%.

Note

: The Slide Indicator Transducers may vary a considerable amount with temperature

change, and therefore they need to be calibrated at typical running temperatures.