SYMPTOM CONDITION CHECKS ACTIONS NOTES
TROUBLE SHOOTING INFORMATION
1. BLOWER STAYS ON HIGH
SPEED WHEN IGNITION IS ON
BLOWER STAYS ON HIGH
SPEED WHEN IGNITION IS ON
OR OFF
2. COMPRESSOR WILL NOT TURN
ON (ALL OTHER FUNCTIONS
WORK)
SYSTEM IS NOT CHARGED
SYSTEM MUST BE CHARGED FOR COMP. TO
ENGAGE
CHARGE SYSTEM OR BYPASS PRESSURE SWITCH.
CHECK TWO PIN CONNECTOR AT ECU HOUSING
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 POSTION.
DISCONNECTED OR FAULTY THERMISTOR WILL
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.
REPLACE RELAY
CHECK FOR FAULTY A/C RELAY
CHECK CONTINUITY TO GROUND ON WHITE CONTROL
HEAD WIRE. CHECK FOR 5V ON RED CONTROL HEAD
WIRE.
DANGER- NEVER BYPASS SAFETY SWITCH WITH
ENGINE RUNNING, SERIOUS INJURY CAN
RESULT.
CHECK FOR FAULTY A/C POT OR ASSOC. WIRING
(NOT APPLICABLE TO 3 POT CONTROLS
CHECK FOR DISCONNECTED OR FAULTY
THERMISTOR.
NO OTHER FUNCTIONS WORK
ALL OTHER FUNCTIONS WORK
CHECK FOR DAMAGED PINS OR WIRES IN CONTROL
HEAD PLUG.
CHECK FOR DAMAGED GROUND WIRE (WHITE) IN
CONTROL HEAD HARNESS.
CHECK FOR DAMAGED BLOWER SWITCH OR POT
AND ASSOCIATED WIRING.
UNPLUG 3 WIRE BSC CONTROL CONNECTOR
FROM ECU. IF BLOWER SHUTS OFF, ECU IS EITHER
IMPROPERLY WIRED, OR DAMAGED.
UNPLUG 3 WIRE BSC CONTROL CONNECTOR
FROM ECU. IF BLOWER STAYS RUNNING, THE BSC
IS EITHER IMPROPERLY WIRED, OR DAMAGED.
VERIFY ALL PINS ARE INSERTED INTO PLUG. INSURE NO
PINS ARE BENT OR DAMAGES IN ECU.
LOSS OF GROUND ON THIS WIRE RENDER
CONTROL HEAD IN OPERABLE
SEE BLOWER SWITCH CHECK PROCEDURE
NO OTHER PART REPLACEMENTS SHOULD BE
NECESSARY
VERIFY CONTINUITY TO CHASSIS GROUND WITH WHITE
CONTROL HEAD WIRE AT VARIOUS POINTS
BE SURE SMALL, 20 GA WHITE GROUND WIRE IS
CONNECTED TO THE BATTERY GROUND POST. IF IT IS,
REPLACE ECU.
REPLACE BSC. (THIS WILL REQUIRE EVAPORATOR TO BE
REMOVED FROM VEHICLE.)
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.
