63
Unloader Head
Operation
During normal operation, the unloader head
allows refrigerant to pass from the discharge valve
plates through the check valve located in the head.
The solenoid valve is de-energized in this
position. Discharge pressure passes from Port “A”
through the solenoid valve to the center port, Port
“C”, which forces the unloader piston down and
seals up the discharge hole to the suction cavity.
During the unload operation, the unloader
solenoid is energized, the pressure passes from
Port “B” to Port “C”. This allows the refrigerant
to pass from the suction chamber to the top of the
unloader. This reduction in pressure and the
spring in the unloader piston allows the valve to
lift. This will cause the refrigerant to pass back
into the suction cavity of the compressor at the
same time the check valve located in the head
seats and prevents the discharge pressure from
short cycling in the compressor. This continues
until the solenoid de-energizes. At this time the
discharge pressure builds up, seals off the port to
the suction cavity and the system pumps with four
cylinders.
Check Out
1. With unloader de-energized, compressor
should pump down normally 15 to 20 in. Hg
vacuum (-51 to -68 kPa) and should hold a 15
in. Hg vacuum (-51 kPa) for three minutes.
2. Using an auxiliary battery, energize and
de-energize unloader solenoid on compressor
cylinder head while the compressor is
running. An audible noise will be made when
unloading, as well as a pressure change in
both suction and discharge.
CAUTION: Unloader heads are used on
special compressor bodies that have a
return gas passage. Do not use unloader
heads on compressor bodies that do not
have the return gas passage.
1.
Unloader Valve Cover
2.
Retaining Clip
3.
Check Valve Cover
4.
Unloader Spring
5.
Check Valve Spring
6.
Check Valve Piston
7.
Unloader Cylinder Head
8.
Port “A”
9.
Solenoid
10.
Port “B”
11.
Port “C”
12.
Normal Flow
13.
Unload Flow
14.
Gasket
15.
Unloader Spring Sleeve
16.
Unloader Piston
Figure 103: Unloader Head Components
AGA516
16
14
15
13
12
10
11
8
9
7
6
5
4
3
2
1
