Chevrolet 70 Series 1970, Service Manual

Page: 118 / 841

CAB AND BODY MOUNTINGS 1-87
HEATING SYSTEM
DESCRIPTION
The cab heating s y s te m i s an in tegral unit
designed to provide driver com fort by heating
an d /o r circulating a ir through the cab. F or cabs
equipped with a sle e p e r com partm ent, an au xiliary
h eater is provided.
H eater co re is located in sid e main heater
housing (fig. 42) which i s position ed in cen ter con­
s o le of cab. The sle e p e r h eater co re a ssem b ly is
attached to left r e a r sid e of main heater housing.
The blow er and a ir in let a ssem b ly , attached
below main h eater housing on p a sse n g e r 's sid e of
co n so le i s equipped with two blow er m o to rs. The
b lo w ers circu la te a ir through the main heater
c o re, the s le e p e r h eater co re (if equipped), and
into a i r ducts.
The dual blow er m otors, which a re e le c tr ic ­
a lly connected in p a r a lle l, a r e fed from a fou r-
p osition control sw itch and r e s is to r network. A ll
b low er e le c tr ic a l c ir c u its a r e protected by an
autom atic r e s e t c ir c u it break er. R efer to m aster
w iring diagram on cen ter co n so le a c c e s s cover
when troubleshooting h eater e le c tr ic a l c ir c u its.
IMPORTANT: B efo re attem pting to rem ove
any e le c tr ic a l com ponent, be su re to pull out r e se t
button on m aster c ir c u it breaker to allow s e r v ic e
to h eater w iring without danger of shorting out. A
w hite ring around b a se of button is v isib le when
m a ste r circu it b reak er is open.
AIR CIRCULATION (F ig . 42)
O utside air en ters heating sy ste m through a
louvered opening located on v eh ic le front panel b e­
tw een right headlight and g r ille . A ir flow then
p a s s e s beneath cab floor through an a ir intake duct
into the blow er and a ir in let a ssem b ly . F rom the
b lo w ers, a ir is fo rce d into the main h eater housing,
a ir distributor a sse m b ly , and out through h eater
and d efro ster ducts. If cab is equipped with s le e p e r
com partm ent, a ir from b low ers is a lso d irected
through the sle e p e r h eater core into ducts that
lead to rear co rn er ou tlets in sle e p e r com partm ent.
Volume of outside a ir entering heating sy ste m
i s con trolled by a dam per valve p osition ed at en­
tra n ce of blow er housing a ssem b ly .
NOTE: Operation of individual h eater con trols
is d escrib ed in "Operating Instructions" la te r in
th is sectio n .
COOLANT CIRCULATION (F ig. 43)
Engine coolant i s fo r c e -c ir c u la te d through
h eater co re(s) a s a r e su lt of p r e ssu r e from engine
w ater pump. For the standard cab, hot coolant from
bottom of w ater filte r flow s through a fle x ib le hose
into m ain heater co re and is returned to connection
at top of w ater f ilte r . F or sle e p e r com partm ent
ca b s, the coolant le a v e s the main h eater co re and
p a s s e s through the sle e p e r heater c o re before
being returned to the engine (fig. 44). The flow of
coolant through main h eater c o r e supply lin e is
controlled by a w ater valve when veh icle is equip­
ped with a ir conditioning.
OPERATION INSTRUCTIONS
(R efer to F igu re 42)
The heating sy ste m i s con trolled by th ree
le v e r s and a fou r-p osition fan sw itch . A ll con trols
a r e located on the co n so le to the right of the gauge
panel.
W ARNING-CARBON M O N O XID E
To keep out offensive odors and ex­
haust gases when in congested traffic, or
parked behind a vehicle with its motor
running, close outside a ir intake ventila­
tors. An outside a ir intake is used with
heater. Close this intake to minimize in­
troduction of contaminated a ir into cab;
this is accomplished by moving "AIR"
lever on heater control panel to "R EC IR ."
position. Avoid inhaling exhaust gases
when any concentration of these is present
in the a ir; i.e., in a garage or when parked
for extended periods with engine running.
Exhaust gases have strong odors which
normally should give warning of their
presence. However, the exhaust gases
from some vehicles may not be so notice­
able under certain conditions and the
senses of people react differently. Exhaust
gases contain a percentage of carbon mon­
oxide which is a poisonous gas that, by
itself, is tasteless, colorless, and odorless.
1. The "AIR" le v e r co n tro ls the so u rce of air
through sy ste m . P ush knob up for outside air; push
knob down to re c ir cu la te in sid e a ir . Interm ediate
p o sitio n s of le v e r w ill resu lt in a proportional
m ixture of ou tsid e and recircu la ted air flow through
sy s te m .
2. The "HTR" le v e r con trols the d irection of
a ir flow from sy ste m . P ush knob up to d irect air
flow through h eater outlets; push knob down to
d irect a ir flow through d efro ster o u tlets. Interm ed­
iate p o sitio n s of le v e r w ill r e su lt in proportional
am ounts of a ir flow through both h eater and de­
fr o s te r o u tlets.
3. The "TEMP" le v e r d ir e c ts a ir flow either
around or through the m ain h eater c o re, or through
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL