McQuay MicroTech Unit Controller Installation And Maintenance Data page 20

STARTING THE CENTRIFUGAL COMPRESSOR
Prior to starting the compressor, all procedural steps normally
associated with starting a newly installed machine must be
followed. For detailed recommendations, see McQuay SM001
and IM 392 covering general start-up and the IQ-1000 solid-
state overload.
The proper direction of compressor motor rotation is vital,
and may be determined:
1. By means of a phase sequence test device.
2. By "bumping" the motor momentarily while visually obser-
ving the direction of the motor rotation.
With a MicroTech control panel, a machine may be
"bumped" only after all other start-up steps are completed.
by starting the machine with a 115 volt control lead and
pushbutton switch connected between terminals 25 at the
starter and 25 at the MicroTech control panel. The normal in-
terconnecting lead must be disconnected at either end and
the end taped temporarily.
The pushbutton switch should be a thumb-held button.
pressed and held to complete the circuit, suitable for 115 volts.
50 VA. It should be connected to 115 volt wiring long enough
to reach comfortably between the control panel connection
and a point at the compressor motor end cover where the start-
up technician can interrupt motor power instantly as the motor
begins to turn.
The sequence of timed functions such as "evaporator pump
on", " waiting for load", and "oil pump" pre-lube provide ade-
quate time for the technician to get into place at the motor
Figure 20. Keypad.
Page 20 / 403
IM
end cover sigh: glass. The direction of the motor rotation can
now be determined within a few electrical cycles after the MCR
coils close energizing the compressor. The technician should
then immediately release the "bump" switch, opening the cir-
cuit to the MCR relays and stopping the compressor.
Following completion of this last verification step (direction
of motor rotation), shut off the control circuit power at its
source. disconnect the "bump" switch wiring and reconnect
conventional control wiring.
Prior to re-connecting control power and energizing the
compressor power circuit, it is often possible and desirable
to set the current transformer circuits' variable reisistor follow-
ing a quick calculation. Using the compressor RLA, and the
current transformer's primary to secondary ratio, calculate the
resistance in ohms required to produce 5 volts AC.
Transf. Sec. Ratio
x .~. _ i._.__ x
1 RLA j1.0, .50 or 581'=CT output a m p s
Ratio
Transf. Pr imary
*
If the current transformer in the main line use 10; use 058 if the CT
IS
in a phase leg (Star-Delta starters): use .50 i f dual conductors are used on
across the line or, autotransformer starters and only one lead out of s i x i s pass-
ed through the CT
2 Calculate the required ohms from the CT output amps as
follows
5 Volts
Resistance m
ohms
CT output amps
Since the MicroTech panel will accept between 5.0 and 7.0 volts
AC, recalculate step 2) using 7 volts
IS