Chevrolet 10 Series 1970, Service Manual

Page: 632 / 671

ACCESSORIES 15-2
r e le a s e sw itches a re provided: an E le c tr ic Switch d is ­
engages the R egu lator unit and a Vacuum Switch d e­
c re a s e s the vacuum in the Servo unit to quickly return
the throttle to id le position.
The operation o f each unit o f the system and the o p era ­
tion o f the en tire system under va riou s circu m stan ces
is d escrib ed below . F igu re 1 shows the location o f the
system components within the veh icle.
C O M P O N E N T O PERA TION
ENGAGEMENT SWITCH
T h is switch, located within the turn signal knob, has
th ree positions. In the fu lly re le a s e d position, the switch
p a sses cu rren t through resista n ce w ire to e ffe c t a "h o ld
in " m agnetic fie ld in the R egu lator solenoid. T h is cu r­
rent is su fficien t only to hold the solenoid in place once
it has been actuated by the "p u ll in” c irc u it. D ep ressin g
the button p a rtia lly a llow s current to flo w to the R egu­
la to r solenoid at fu ll voltage which causes the solenoid
to pull in. D ep ressin g the button fu lly opens the circu it
to both the resista n ce and standard solen oid feed w ire s
and the solenoid b ecom es de-activated .
During ve h ic le operation the th ree sw itch positions
have the fo llo w in g functions:
Released
a. System not engaged: No function o f the system
w ill occu r although a sm all current is flow ing
through the solen oid v ia the resista n ce w ire .
b. System engaged: The sm all cu rren t flow ing
through the resista n ce w ire is holding the s o le ­
noid in the engaged position.
P a rtially Depressed
Full voltage is applied to the solenoid (veh icle speed
o v e r 35 M P H ) which sets the R egu lator to maintain the
v e h ic le speed at the tim e o f R egu lator engagem ent.
Fully Depressed
No e le c tr ic ity flow s to the solen oid and the R egu lator
is inactive. T h is position is used by the d r iv e r when he
d e s ire s to ra is e o r lo w e r his con trolled speed. He may
a c c e le ra te to his new speed, p re s s the button fu lly (regu ­
la to r re le a s e s p re v io u s ly set speed) and re le a s e the but­
ton. Upon re le a s in g the button, it p asses through the
p a rtia lly depressed position and the solen oid is “ pulled
in” , then into re le a s e d position which p ro vid es "h o ld in”
current. The d r iv e r may also p re s s the button fu lly with
no p ressu re on the a c c e le ra to r pedal. In this case the
regu la to r re le a s e s control o f the th rottle which returns
to idle and the ca r slow s. When the button is relea sed
the solenoid is pulled in and held in r e s p e c tiv e ly and the
reg u la to r resu m es speed con trol at the speed o f the
v e h icle during the moment o f button r e le a s e (at veh icle
speeds o v e r 35 M P H ).
BRAKE RELEASE SWITCHES
T w o brake re le a s e sw itches are em ployed in the C ruise
M a ster System. When the brake pedal is depressed, an
E le c tr ic R elea se Switch cuts o ff the voltage supplied to
the engagement switch, hence cuts o ff pow er to the R egu ­
la to r unit. The R egu lator is then disengaged and req u ires
Engagem ent Switch operation to return it to operation.
A Vacuum R e le a s e Switch operates sim ultaneously with
the e le c tr ic re le a s e switch w henever the brake pedal is
d epressed. T h is sw itch opens a p ort to atm ospheric
p ressu re which rap id ly bleeds down the vacuum in the
S erov unit th ereby returning the th rottle to the idle
position.
C1UTCH RELEASE SWITCH
Figu re 9 also shows a Clutch Switch in the w irin g
harness. T h is sw itch is used on C ru ise M a ster units on
v e h ic le s equipped with manual tran sm ission . The sche­
m atic o f C ru ise M a ster w irin g on v e h ic le s equipped with
autom atic tran sm ission , is identical to the d iagram
shown but with the clutch switch bypassed. The clutch
sw itch harness connector is jum pered with a b ra ss clip.
SERVO UNIT
The Servo unit is a vacuum actuated, v a ria b le position
diaphragm assem bly, which op erates t h e ca rb u retor
th rottle when the system is in operation. It is p ow ered by
con trolled vacuum fro m the R egu lator and op erates the
th rottle linkage v ia the bead chain. The S ervo has a p o rt
on the sealed side o f the diaphragm housing. When con­
tr o lle d vacuum is applied to this port, atm osph eric p r e s ­
sure m oves the diaphragm which pulls on the bead chain
opening the ca rb u retor th rottle.
REGULATOR
The R egu lator is a d evice which has two p rim a ry
functions. F ir s t, it is a vacuum sw itch which, when en­
gaged by the d r iv e r , supplies vacuum to a " T e e ” fitting.
Second, it m eters a sm all v a ria b le quantity o f a ir to the
" T e e ” fittin g w here it blends with vacuum, thus providing
the pow er unit with con trolled vacuum which w ill m ain­
tain the selected speed. If the R egu lator begins to supply
le s s b leed a ir (veh icle speed decreasin g) the vacuum in
the cham ber in c rea ses and the diaphragm m oves toward
the vacuum port. If the R egu lator begins to supply m ore
b leed a ir (veh icle speed in crea sin g), the vacuum in the
cham ber drops and the diaphragm m oves away fro m the
vacuum port. In operation, at cru ise speed, a prop er
CHEVROLET TRUCK SERVICE MANUAL