Chevrolet 10 Series 1970, Руководство по обслуживанию

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HEATER AND AIR CONDITIONING 1A-21
• Check the switch adjusting screw fo r stripped or
oth erw ise damaged threads*
A djusting Switch
If, a fte r the above checks, the switch seem s to be op­
era tin g p ro p e rly , adjust fo r p ro p er setting if n ecessary,
as fo llo w s :
1. V eh icle must be set up as d escrib ed in " P e r fo r m ­
ance T e s t ."
2. The suction side of the system , read on the low
p ressu re gauge, should pull down to the pressu re
shown in the chart in "P e rfo rm a n c e Data" under the
ambient tem peratu re at the tim e the switch is being
set.
3. R oof-M ounted System - R em ove the r e a r duct screw s
and then rem ove the duct fro m its side retaining
flan ges. It is not n ecessa ry to rem ove the duct
fro m its re a r retaining flange o r disconnect the re a r
drain tubes.
GM C h evrolet System - L o w er the en tire unit fro m
its dash mounting, rem o ve the duct assem bly from
the b lo w e r-e v a p o ra to r unit and then rem ove the duct
r e a r cover.
4. D isconnect the switch w irin g harness, rem ove the
sw itch attaching screw s and rem ove the switch.
NOTE: On GM C h evro let Units, the knob must
be pulled o ff the switch shaft b efo re the switch
can be rem oved.
5. R em ove the switch non-m etal end plate to gain ac­
cess to the switch adjusting screw .
6. If the outlet tem peratu re was le s s than the p r e ­
s crib ed tem peratu re at the end o f each cooling cycle,
turn the adjusting sc re w a p a rtia l turn counter­
clock w ise (fig. 31). If the outlet tem perature was
m o re than p re s c rib e d tem peratu re, turn the adjusting
s c re w clockw ise.
NOTE: One turn of the adjusting s c re w w ill
change the outlet tem peratu re approxim ately 4
d egrees.
7. R ein sta ll switch end plate and in sta ll switch. R ein­
s ta ll ducts rem oved in Step 3 above. Be sure that
the a ir sensing c a p illa ry has been rep laced p ro p e rly ,
if rem oved during disassem bly.
8. Check system p erform an ce. If fu rther adjustment
is needed, repeat Steps 3 through 7 until the p r e ­
scrib ed p ressu re is reached.
C A UTIO N: Do not attempt to run a P e r fo r m ­
ance Check with the system disassem bled since
inaccurate readings would be the result.
A L ­
W A Y S rein sta ll the duct work b efo re running a
p erform an ce check.
EXPANSIO N VALVE (Fig. 3 2 )
A malfunction o f the expansion va lve w ill be caused by
one o f the follow in g conditions; va lve stuck open, va lve
stuck closed, broken pow er elem ent, a re s tric te d screen
o r an im p ro p erly located o r installed pow er elem ent bulb.
The fir s t three conditions req u ire va lve replacem ent.
The last two may be c o rre c te d by replacing the va lve inlet
screen and by p ro p e rly installing the pow er elem ent bulb.
Attachment of the expansion va lve bulb to the e vaporator
outlet pipe is v e r y c ritic a l. The bulb must be attached
tightly to the pipe and must make good contact with the
pipe along the en tire length of the bulb. A loose bulb w ill
resu lt in high P O A p re ssu res and poor cooling. On
bulbs located outside the evaporator case, insulation must
be p ro p e rly installed.
Indications o f expansion va lve trouble provided by the
P erfo rm a n ce T e s t a re as fo llo w s:
V A L V E STU CK O PE N
N o isy C om pressor.
No Cooling - F r e e z e Up.
V A L V E STU CK CLOSED, P L U G G E D SCREEN OR
BRO KEN PO W ER E L E M E N T
V e r y Low Suction P re s s u re .
No Cooling.
CAPILLARY BULB
EXTERNAL
EQUALIZER
LINE
OUTLET
F ig . 3 1 —T h e rm o sta tic S w itc h A d ju stm e n t
F ig . 3 2 — Expansion V a lv e
CHEVROLET TRUCK SERVICE MANUAL