Jeep Cherokee 1999 Electronic Service Manual page 1224

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DESCRI PT I ON AN D OPERAT I ON (Cont inue d)
Fig. 10 Vehicle Speed Sensor Location—2WD—
Fig. 11 Vehicle Speed Sensor Location—4WD—
AIR CONDITIONING (A/C) CLUTCH RELA Y—
PCM OUTPUT
Th e A/C r ela y is loca t ed in t h e P ower Dist r ibu t ion
Cen t er (P DC). Th e P DC is loca t ed in t h e en gin e com -
pa r t m en t (F ig. 12). Refer t o la bel on P DC cover for
r ela y loca t ion .
Typical
Typical
Fig. 12 Power Distribution Center (PDC)
Th e power t r a in con t r ol m odu le (P CM) a ct iva t es t h e
A/C com pr essor t h r ou gh t h e A/C clu t ch r ela y. Th e
P CM r egu la t es A/C com pr essor oper a t ion by swit ch -
in g t h e gr ou n d cir cu it for t h e A/C clu t ch r ela y on a n d
off.
Wh en t h e P CM r eceives a r equ est for A/C fr om A/C
eva por a t or swit ch , it will a dju st idle a ir con t r ol (IAC)
m ot or posit ion . Th is is don e t o in cr ea se idle speed.
Th e P CM will t h en a ct iva t e t h e A/C clu t ch t h r ou gh
t h e A/C clu t ch r ela y. Th e P CM a dju st s idle a ir con t r ol
(IAC) st epper m ot or posit ion t o com pen sa t e for
in cr ea sed en gin e loa d fr om t h e A/C com pr essor.
By swit ch in g t h e gr ou n d pa t h for t h e r ela y on a n d
off, t h e P CM is a ble t o cycle t h e A/C com pr essor
clu t ch . Th is is ba sed on ch a n ges in en gin e oper a t in g
con dit ion s. Th e P CM will a lso de-en er gize t h e r ela y if
coola n t t em per a t u r e exceeds 125°C (257°F ).
AUTO SHUTDOWN (ASD) RELA Y—PCM
OUTPUT
DESCRIPTION
Th e ASD r ela y is loca t ed in t h e P ower Dist r ibu t ion
Cen t er (P DC).
OPERA TION
Th e ASD su pplies ba t t er y volt a ge t o t h e fu el in jec-
t or s a n d ign it ion coil(s). Wit h cer t a in em ission s pa ck-
a ges it a lso su pplys volt a ge t o t h e oxygen sen sor
h ea t in g elem en t s. Th e gr ou n d cir cu it for t h e coil in
t h e ASD r ela y is con t r olled by t h e P ower t r a in Con -
t r ol Modu le (P CM). Th e P CM oper a t es t h e r ela y by
swit ch in g t h e gr ou n d cir cu it on a n d off.
FUEL SYSTEM 14 - 33