Chevrolet 70 Series 1970, Service Manual

Page: 43 / 841

CAB AND BODY MOUNTINGS 1-12
Series Winding Shunt Winding D ajh Switch
i— s f -
24 OHM
Resistor
„LV
■—
f=Qn
- Battery Armature
Park Switch
LOW SPEED CIRCUITS
Series Winding Shunt Winding Dash Switch
( Gray )
Battery
HIGH SPEED CIRCUITS
Park Switch
T-2558
Figure 7 2—High-Low Speed Circuits
and pinion a ssem b ly , and an output gear and shaft
a ssem b ly . The crank arm is attached to the output
gear shaft.
Two sw itch e s, a control sw itch on dash and a
parking sw itch within w iper unit, control the sta r t­
ing and stopping of w ip er. Parking sw itch contacts,
located on a term in al board at bottom of drive unit
a re actually connected a c r o ss the dash sw itch and
act a s a s e t of holding contacts when the dash
sw itch is turned off. This keeps the w iper circu it
c lo sed so w iper can keep operating until the blades
reach th eir p redeterm ined "PARK" position .
When the w ip ers a re turned on, current flow s
from battery through the circu it breaker or fu se
through the m otor fie ld and arm ature to the dash
sw itch and on to ground, startin g the w iper.
NOTE: R efer to "Windshield W asher” la ter in
th is sectio n for operation of w a sh ers.
TWO-SPEED OPERATION (F ig s. 11 and 12)
Low Speed Operation
When the dash sw itch is placed in "LOW"
sp eed position , current from the battery flow s
through the s e r ie s fie ld c o il and divides; part p a s s ­
ing through the shunt fie ld c o il to ground at the
dash sw itch, the rem aining part p assin g through
the arm ature to ground at the dash sw itch .
High Speed Operation
Moving the dash sw itch to "HIGH" sp eed p o s i­
tion opens the shunt fie ld c ircu it to ground at dash
sw itch and keeps the arm ature circu it clo sed to
ground. The shunt field current m ust then p a ss
through a r e s is to r located on the w iper term inal
N O TE: T e rm in a ls A re N um bered
For Pu rpo ses
of
E x p la n a tio n
LO SP EED —A s Sh ow n
HI SP EED — D isconnect Ju m p e r W ire
From Term in a l N o. 3
O F F —Leave Ju m p e r Connected to
T e rm in a ls 1 a n d 3 But D isconnect
it From G ro und
For Bench Testing
Connect to
Wiper Housing
Ammeter
T-030
Figure 13—Troubleshooting Wiper Motor Circuit
board, and then through the sa m e lead that connects
the arm ature circ u it to ground through the dash
sw itch.
P arking C ircuit
When w iper is turned off, circu it is broken at
the dash sw itch . H ow ever, current from battery
continues to flow through m otor, through the park­
ing sw itch contacts to ground. When w iper blades
reach "PARK" p osition at the inboard end of wiper
pattern, the parking sw itch contacts open, stopping
the m otor.
TROUBLESHOOTING WIPER MOTOR
R efer to fig u res 11, 12, and 13 when trouble­
shooting tw o -sp e ed w ip er.
TYPICAL TROUBLE CONDITIONS
1. W iper w ill not shut off.
2. W iper in op erative.
3. Wiper has one speed (HIGH).
4. W iper has one sp eed (LOW) and shuts off
w ith dash sw itch in "HIGH" position .
5. B lad es do not return to "PARK" p osition
when w iper is turned "OFF."
6
. W iper sp eed norm al in "LOW" sp eed p o s i­
tion but too fa st in "HIGH" sp eed p o sitio n .
7. W iper op erates interm ittently.
CHECKING INSTALLED WIPER
Wiper W ill Not Shut Off
1. D eterm in e if w ip er op erates in both "HIGH"
and "LOW" sp eed s. "LOW" sp eed only, or "HIGH"
sp eed only.
IMPORTANT: W iper m ust operate in "LOW"
sp eed during parking c y c le .
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL