Page 6
Revised 05−2009
TPA*S4
Diagnostic LEDs
The defrost board uses two LEDs for diagnostics. The LEDs
flash a specific sequence according to the condition.
TABLE 1
Defrost Control Board Diagnostic LED
Mode
Green LED (DS2)
Red LED
(DS1)
No power to control
OFF
OFF
Normal operation /
power to control
Simultaneous Slow FLASH
Anti-short cycle lock-
out
Alternating Slow FLASH
Low pressure switch
fault (Optional)
OFF
Slow FLASH
Low pressure switch
lockout (Optional)
OFF
ON
High pressure switch
fault (Optional)
Slow FLASH
OFF
High pressure switch
lockout (Optional)
ON
OFF
B − Compressor
All TPA*S4 units utilize a scroll compressor. The scroll
compressor design is simple, efficient and requires few
moving parts. A cutaway diagram of the scroll compressor is
shown in figure 5. The scrolls are located in the top of the
compressor can and the motor is located just below. The oil
level is immediately below the motor.
The scroll is a simple compression concept centered around
the unique spiral shape of the scroll and its inherent properties.
Figure 6 shows the basic scroll form. Two identical scrolls are
mated together forming concentric spiral shapes (figure 7).
One scroll remains stationary, while the other is allowed to
"orbit" (figure 8). Note that the orbiting scroll does not rotate or
turn but merely orbits the stationary scroll.
FIGURE 5
SCROLL COMPRESSOR
DISCHARGE
SUCTION
NOTE − During operation, the head of a scroll compressor may
be hot since it is in constant contact with discharge gas.
FIGURE 6
SCROLL FORM
FIGURE 7
STATIONARY SCROLL
ORBITING SCROLL
DISCHARGE
SUCTION
CROSS−SECTION OF SCROLLS
TIPS SEALED BY
DISCHARGE PRESSURE
DISCHARGE
PRESSURE
The counterclockwise orbiting scroll draws gas into the outer
crescent shaped gas pocket created by the two scrolls (figure
8 − 1). The centrifugal action of the orbiting scroll seals off the
flanks of the scrolls (figure 8 − 2). As the orbiting motion
continues, the gas is forced toward the center of the scroll and
the gas pocket becomes compressed (figure 8 − 3). When the
compressed gas reaches the center, it is discharged vertically
into a chamber and discharge port in the top of the compressor
(figure 7). The discharge pressure forcing down on the top
scroll helps seal off the upper and lower edges (tips) of the
scrolls (figure 7). During a single orbit, several pockets of gas
are compressed simultaneously providing smooth continuous
compression.
The scroll compressor is tolerant to the effects of liquid return.
If liquid enters the scrolls, the orbiting scroll is allowed to
separate from the stationary scroll. The liquid is worked toward
the center of the scroll and is discharged. If the compressor is
replaced, conventional Lennox cleanup practices must be
used.
Due to its efficiency, the scroll compressor is capable of
drawing a much deeper vacuum than reciprocating
compressors. Deep vacuum operation can cause
internal fusite arcing resulting in damaged internal parts
and will result in compressor failure. Never use a scroll
compressor for evacuating or pumping−down" the
system. This type of damage can be detected and will
result in denial of warranty claims.
The scroll compressor is quieter than a reciprocating
compressor, however, the two compressors have much
different sound characteristics. The sounds made by a
scroll compressor do not affect system reliability,
performance, or indicate damage.
See compressor nameplate and ELECTRICAL DATA
table on page 2 for compressor specifications.
