Service Manual

PRODUCT DESIGN
17
- Compliant scroll compressors perform “quiet” shutdowns
that allow the compressor to restart immediately without
the need for a time delay. This compressor will restart
even if the system has not equalized.
- Operating pressures and amp draws may differ from
standard reciprocating compressors. This information
may be found in the “Cooling Performance Data” section.
All models of the A/GPG16 series package units use a 2
stage scroll compressor. The basic scroll design has been
modified with the addition of an internal unloading mechanism
that opens a by-pass port in the first compression pocket,
effectively reducing the displacement of the scroll. The
opening and closing of the by-pass port is controlled by an
internal electrically operated solenoid.
The ZPS modulated scroll uses a single step of unloading
to go from full capacity to approximately 67% capacity. A
single speed, high efficiency motor continues to run while
the scroll modulates between the two capacity steps.
A scroll is an involute spiral which, when matched with a
mating scroll form as shown, generates a series of crescent
shaped gas pockets between the two members.
During compression, one scroll remains stationary (fixed
scroll) while the other form (orbiting scroll) is allowed to orbit
(but not rotate) around the first form.
As this motion occurs, the pockets between the two forms
are slowly pushed to the center of the two scrolls while
simultaneously being reduced in volume. When the pocket
reaches the center of the scroll form, the gas, which is now
at a high pressure, is discharged out of a port located at the
center.
During compression, several pockets are being compressed
simultaneously, resulting in a very smooth process. Both the
suction process (outer portion of the scroll members) and the
discharge process (inner portion) are continuous.
ELECTRICAL WIRING
The units are designed for operation on 60 hertz current and
at voltages as shown on the rating plate. All internal wiring
is complete. Ensure the power supply to the compressor
contactor is brought to the unit as shown on the supplied unit
wiring diagram. The 24V wiring must be connected between
the unit control panel and the room thermostat.
LINE VOLTAGE WIRING
Power supply to the unit must be N.E.C. Class 1, and must
comply with all applicable codes. The unit must be electri-
cally grounded in accordance with the local codes or, in their
absence, with the latest edition of the National Electrical
Code, ANSI/NFPA No. 70, or in Canada, Canadian Electrical
Code, C22.1, Part 1. A fused disconnected must be provided
and sized in accordance with the unit minimum circuit
ampacity.
The best protection for the wiring is the smallest fuse or
breaker which will hold the equipment on line during normal
operation without nuisance trips. Such a device will provide
maximum circuit protection.
WARNING
DO NOT EXCEED THE MAXIMUM OVERCURRENT
DEVICE SIZE SHOWN ON THE UNIT DATA PLATE.
All line voltage connections must be made through weather
proof fittings. All exterior power supply and ground wiring
must be in approved weather proof conduit. Low voltage
wiring from the unit control panel to the thermostat requires
coded cable. See the following figures for ground level and
rooftop wiring.