Vintage 1967-72 CHEV PICK-UP Spécifications télécharger pdf (Page 20)

901149 REV D 7/30/14, INST 67-72 CHEVY PICKUP wo AC EVAP KIT PG 20 OF 24

Symptom Condition Checks Actions Notes

Blower stays on

high speed when

ignition is on.

1a.

No other functions work.

Check for damaged pins or

wires in control head plug.

Verify that all pins are inserted into plug. Ensure that no

pins are bent or damaged in ECU.

Check for damaged ground

wire (white) in control head

harness.

Verify continuity to chassis ground with white control

head wire at various points.

Loss of ground on this wire

renders control head

inoperable.

All other functions work.

Check for damaged blower

switch or potentiometer and

associated wiring.

Blower stays on

high speed when

ignition is on or off.

Unplug 3-wire BSC control

connector from ECU. If blower

shuts off, ECU is either

improperly wired or damaged.

Be sure the small, 20 GA white ground wire is connected

to the battery ground post. If it is, replace the ECU.

Unplug 3-wire BSC control

connector from ECU. If blower

stays running, BSC is either

improperly wired or damaged.

Check to ensure that no BSC wiring is damaged or

shorted to vehicle ground. The BSC operates the blower

by ground side pulse width modulation switching. The

positive wire to the blower will always be hot. If the

“ground” side of the blower is shorted to chassis ground,

the blower will run on HI.

Replace BSC (This will require removal of evaporator

from vehicle).

No other part replacements

should be necessary.

Compressor will

not turn on

(All other functions

work).

System is not charged.

System must be charged for

compressor to engage.

Charge system or bypass pressure switch.

Danger: Never bypass

safety switch with

engine running. Serious

injury can result.

System is charged.

1b.

Troubleshooting Guide

Check for faulty A/C

potentiometer or associated

wiring (Not applicable to 3-pot

controls).

Check for disconnected or

faulty thermistor.

Check continuity to ground on white control head wire.

Check for 5V on red control head wire.

Check 2-pin connector at ECU housing.

To check for proper pot

function, check voltage at

white/blue wire. Voltage

should be between 0V and

5V, and will vary with pot

lever position.

Disconnected or faulty

thermistor will cause

compressor to be

disabled.

Red wire at A/C pot should

have approximately 5V

with ignition on. White

wire will have continuity to

chassis ground. White/

Blue wire should vary

between 0V and 5V when

lever is moved up or down.

Compressor will

not turn off

(All other functions

work).

Check for faulty A/C

potentiometer or associated

wiring.

Check for faulty A/C relay.

Repair or replace pot/control wiring.

Replace relay.

See blower switch check

procedure.

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Vintage 1967-72 CHEV PICK-UP Spécifications Page 20

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