Chevrolet DB90 Series, Service Manual

Page: 124 / 242

S ec. 6Y-118
STARTING SYSTEM
Figure 4 —Starting System (Series DP 90)
rela y contact points to ground. With windings en er­
g ized , the m agnetic sw itch contacts c lo se to com ­
p lete circu it from battery to sta rter solenoid o p er­
ating co il causing norm ally open contact points to
c lo s e and com plete circu it from battery to sta rter
solen oid . With solen oid energized, sta r te r w ill
operate.
When engine is started , current from gen er­
ator "R” term inal w ill flow through frequency
sen sin g relay condenser and operating c o il causing
rela y contacts to open, thus breaking the circu it
betw een the battery and sta r ter magnetic sw itch.
NOTE: The condenser and r e sisto r in the f r e ­
quency sen sin g relay w ill determ ine at what f r e ­
quency the relay contacts w ill open.
SERIES JB /M B /M C 90
A typical interlock sy ste m used on th ese v e ­
h ic le s is shown in figu re 3.
When control sw itch is placed in "START"
position , current w ill flow through sta rte r m ag­
n etic control sw itch coil windings and the norm ally
c lo se d voltage sen sin g relay contact points to
ground. With windings energized, the m agnetic
sw itch contacts w ill c lo se to com plete circu it from
battery to sta rter solen oid operating c o il causing
norm ally open sw itch contact points to c lo se and
com plete circu it from battery to sta r te r solenoid.
With solen oid en ergized , sta r ter w ill operate.
NOTE: A diode is in stalled a c r o ss the sta rter
m agnetic sw itch to protect the contact points.
When engine is started , current from gen er­
ator ”R" term inal w ill flow to ground through volt­
age sen sin g relay operating co il causing norm ally
Figure 5 —Circuit For Checking M otor Free Speed
c lo se d contact points to open, thus breaking the
circu it between the battery and m agnetic sw itch.
SERIES PARALLEL STARTER
M AGNETIC SWITCH (SERIES DP90)
A s e r ie s p a ra lle l sta rter m agnetic sw itch is
used on s e r ie s DP90 equipped with the 12V-71
engine to provide 24 volts for the cranking circu it
(fig. 4).
When control sw itch is placed in "IGN” p o s i­
tion and sta r te r sw itch is en ergized , current from
No. 1 circu it breaker w ill flow through sta r te r
sw itch and No. 7 term inal on the s e r ie s p a ra llel
sw itch to ground through the fuel p r e ssu r e sw itch
to en erg ize the s e r ie s p a ra llel sw itch c o il winding.
A diode is in sta lled between No. 6 and No. 7 te r m ­
inal on the sw itch to protect the fuel p r e ssu r e
sw itch con tacts.
With windings en ergized , norm ally open sw itch
contacts w ill c lo se and current from No. 5 term ­
inal on sw itch w ill flow through clo se d contact
points and No. 4 sw itch term in al to provide 24
v o lts to en erg ize the sta r te r solen oid . With s o le ­
noid en ergized , the sta r te r w ill operate.
When engine is sta rted and fuel p r e ssu r e
sw itch opens, the s e r ie s p a ra lle l sw itch contacts
w ill c lo s e . Current from generator "BAT" term inal
w ill then flow through No. 2 and No. 3 term inals
on the s e r ie s p a ra llel sta r te r m agnetic sw itch to
charge the b atteries.
STARTER FREE SPEED CHECK
The fr e e speed check is recom m ended after a
starting m otor has been overhauled. If n e c e ssa r y ,
te s t equipment is available, accom p lish the follow ­
ing ste p s to perform the fr e e sp eed check. R efer
to figure 5 for te s t connections.
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL SUPPLEMENT