ADJUSTMENTS
ADJUSTING AND CALIBRATING
CURRENT LIMIT CALIBRATION
The current limit feature of the control module functions to
limit the maximum compressor motor current and is set at
100% amperes with the compressor at full load. The follow-
ing procedure will properly set this feature:
1.
2.
3.
4.
5.
6.
7.
Remove the cover from Control Module. (See Figure 5).
Place the AUTO/MAN switch in MAN position. This switch
position effectively disconnects the temperature control
function and permits manual loading and unloading of the
compressor.
Adjust the Ramp Up Start Point to 100 (fully counterclock-
wise) and set Ramp time to MIN.
Rotate Percent Current knob fully clockwise.
Using the LOAD/UNLOAD switch, manually load the com-
pressor until the motor current is at rated load amperes.
(Refer to RLA on compressor nameplate).
With full load current on the motor, adjust the blue CUR-
RENT CAL. potentiometer in a clockwise rotation until the
amber light on the module comes on. If the red unload
light comes on, back off the setting until only the amber
light is lit. A quick check can be made with a voltmeter
across terminals OP2 and COM of the module. This
voltage should be about 10 VDC.
Stop compressor, rotate metal indicator on percent cur-
rent shaft to 100% on the scale. Install cover to module,
remove end cap from percent current knob, loosen
knob/shaft screw and align the knob indicator line with
100% on the module cover.
TEMPERATURE CALIBRATION
The control module has been factory calibrated and normal-
ly requires no field calibration. If field calibration becomes
necessary or a calibration check is desired, remove the cover
and proceed as follows:
The pulse rate setting depends on the volume of chilled
water in the piping loop. The pulse rate is adjustable from
2 (DEC.) to 25 (INC.) pulse per minute. A system with a small
volume can be set at a fast rate and conversely slower for
large systems.
The pulse rate can be set by making an adjustment to the
1.
Place AUTO/MAN switch in MAN position.
2. Operate chiller loading and unloading manually until the
temperature of the leaving chilled water is steady at the
desired control point (for example, 45°F) using a reliable
thermometer.
blue PULSE RATE pot and counting the rate per minute that
the red or green lights come on when the chilled water
temperature is near the control point. Adjust the pot counter-
clockwise to increase pulse rate; clockwise to reduce rate.
CURRENT TRANSFORMER
The current transformer located in the motor starter is used
to generate an A.C. voltage signal which varies directly with
the compressor motor current.
3. Switch the AUTO/MAN switch to AUTO position and quick-
ly position the TEMPERATURE knob to a position where
both the LOAD and UNLOAD lights are off. A voltmeter
between terminals
IO1
and COM on the upper terminal
strip of the module should read 7.5 volts
d.c.
In this mode
the adjustable temperature control pot is set at the actual
chilled water temperature.
This signal is calibrated at the factory or by the McQuay
Service technician performing the initial startup of the chiller.
This signal normally is adjusted to approximately 5 volts
a.c.
corresponding to the Rated Load Ampere (RLA) on the com-
pressor nameplate.
The signal is continuously monitored by the control module
to prevent the motor current from exceeding the full load
amperes.
4. Check the pointer on the shaft against the temperature
scale. It should read the same as the water temperature;
Calibration of this signal, although not complex, can be
if not, rotate the pointer to the proper setting without dis-
hazardous with improper procedures. Therefore, if calibra-
tion is needed, it is recommended that the
McQuay
Service
turbing the shaft positon. technician be called to perform the work.
5. Install cover on module and check knob positon; the mark
should line up with the water temperature. If adjustment
is necessary, remove end cap from temperature knob,
loosen knob/shaft screw and make proper scale alignment.
VANE SPEED ADJUSTMENT
RAMP-UP CALIBRATION
The ramp-up functions to control the loading of the com-
pressor at startup and is initiated automatically each time the
compressor starts. Ramp-up ends when the selected time ex-
pires or when the chilled water temperature reaches the con-
troller setpoint.
The vane speed at which the capacity control vanes open
or close is controlled by the rate of oil bleed-off from the vane
actuating piston. This bleed-off rate is adjustable by position-
ing the needle valves on SA and SB solenoid valves located
in-the lube box.
Screwdriver openings in the left side of the lube box per-
mit access. The upper opening accesses the SB needle valve
for adjusting the vane OPENING speed for loading the com-
pressor (Refer to Figure 6). Turn this screw clockwise to
decrease the vane opening speed and counterclockwise to
Page 18 I IM 307
A maximum ramp-up time of 45 minutes is achieved by set-
ting the START POINT at 0% LOAD and the RAMP TIME
at MAX. Both settings are made on the two dashpots so
marked on the right side of the module. (See Figure 5).
Any combination may be set to control the loading rate to
suit the system requirements. Obviously a START PT set-
ting of 100% effectively voids the ramp function.
It should be remembered that the ramp-up feature controls
the compressor loading by temporarily resetting the current
limit. This override action can be observed during Ramp-Up
control by the alternate lighting of the amber current limit
signal and the green load signal.
Actual ramp-up time with the chilled water temperature
above the control point is determined by the formula:
Ramp-lip Time (min.) =
%
Current
-
%
Start Point) x 45 x Ramp Time Setting
Example:
Ramp Time = 0.
75
Start Point =
30%
%
Current =
1OO%
Ramp
Time=(l.OO
-
0.30)x45x0.75
= 24 minutes
PULSE RATE CALIBRATION
The pulse rate (rate of corrective action) is applied to control
the loading rate. When the leaving chilled water temperature
differs from the control point by
*5”F,
the vanes must be
repositioned at the slowest rate that will maintain stable
control.
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