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SYMPTOM CONDITION CHECKS ACTIONS NOTES
1.
BLOWER STAYS ON HIGH
SPEED WHEN IGNITION IS ON
NO OTHER FUNCTIONS WORK
CHECK FOR DAMAGED PINS OR WIRES IN CONTROL
HEAD PLUG.
VERIFY ALL PINS ARE INSERTED INTO PLUG. INSURE 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 WILL RENDER
CONTROL HEAD INOPERABLE
ALL OTHER FUNCTIONS WORK
CHECK FOR DAMAGED BLOWER SWITCH OR POT
AND ASSOCIATED WIRING.
SEE BLOWER SWITCH CHECK PROCEDURE
(CONTACT VINTAGE AIR TECH SUPPORT)
BLOWER STAYS ON HIGH
SPEED WHEN IGNITION IS ON
OR OFF.
UN-PLUG 3 WIRE BSC CONTROL CONNECTOR
FROM ECU. IF BLOWER SHUTS OFF, ECU IS EITHER
IMPROPERLY WIRED, OR DAMAGED.
BE SURE SMALL, 20GA. WHITE GROUND WIRE IS
CONNECTED TO THE BATTERY GROUND POST. IF IT IS,
REPLACE ECU.
UN-PLUG 3 WIRE BSC CONTROL CONNECTOR
FROM ECU. IF BLOWER STAYS RUNNING, THE BSC
IS EITHER IMPROPERLY WIRED, OR DAMAGED.
CHECK TO INSURE THAT NO BSC WIRING IS DAMAGED OR
SHORTED TO VEHICLE GROUND. THE BSC OPERATES
THE BLOWER BY GROUND SIDE PWM 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 EVAPORATOR TO BE
REMOVED FROM VEHICLE. )
NO OTHER PART REPLACEMENTS SHOULD BE
NECESSARY.
2. COMPRESSOR WILL NOT TURN
ON (ALL OTHER FUNCTIONS
WORK)
SYSTEM IS NOT CHARGED
SYSTEM IS CHARGED
SYSTEM MUST BE CHARGED FOR COMP. TO
ENGAGE.
CHARGE SYSTEM OR BYPASS PRESSURE SWITCH . DANGER- NEVER BYPASS SAFETY SWITCH WITH
ENGINE RUNNING, SERIOUS INJURY CAN RESULT
CHECK FOR FAULTY A/C POT OR ASSOC. WIRING CHECK CONTINUITY TO GROUND ON WHITE CONTROL
HEAD WIRE. CHECK FOR 5V ON RED CONTROL HEAD
WIRE.
TO CHECK FOR PROPER POT FUNCTION, CHECK
VOLTAGE AT WHITE/BLUE WIRE. VOLTAGE
SHOULD BE BETWEEN 0 AND 5V, AND WILL VARY
WITH POT LEVER POSITION.
CHECK FOR DISCONNECTED OR FAULTY
(CHECK FOR FAULTY PRESSURE SWITCH)
THERMISTOR.
CHECK TWO PIN CONNECTOR AT ECU
CHECK CONTINUITY ACROSS SWITCH
HOUSING.
DISCONNECTED OR FAULTY THERMISTOR WILL
REPLACE SWITCH
CAUSE COMPRESSOR TO BE DISABLED.
3. COMPRESSOR WILL NOT TURN
OFF (ALL OTHER FUNCTIONS
WORK)
CHECK FOR FAULTY A/C POT OR ASSOC. WIRING REPAIR/REPLACE POT/CONTROL WIRING RED WIRE @ A/C POT SHOULD HAVE APPROX. 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 AND DOWN.
CHECK FOR FAULTY A/C RELAY REPLACE RELAY
FOR '55-56 CHEV. CHECK FOR PROPER PANEL
CONVERSION. CONTROL LEVERS SHOULD TRAVEL
TO WITHIN 1/8" OF BOTH ENDS OF THE SLOTS.
REFER TO INTSRUCTIONS "'55-56 CONTROL PANEL
CONVERSION REV B 6 17 05" PDF OR 903055-PCA REV C
8/10/05 OR LATER INSRUCTION MANUAL.
EARLY INSTRUCTIONS ON '55-56 CHEV. DID NOT
INCLUDE PANEL MOD PROCEEDURE FOR
CONTROL WITH LOWER POT BRACKET OFFSET
BACK FROM CASTING. IF LEVERS ONLY TRAVEL
2/3 TO 3/4 UP, THIS PROCEEDURE MUST BE
PERFORMED
REPLACE ECU.
20
1969-70 MUSTANG w/o AC GEN IV
901271 REV A 2/11/08, 69-70 MUSTANG w/o AC GEN IV EVAP INSTR PG 20 OF 26