1996 Bronco/F-Series

Section 12-00: Climate Control System, Service

1996 F-150, F-250, F-350, F-Super Duty and Bronco, F-Super Duty Motorhome Chassis Workshop Manual

DIAGNOSIS AND TESTING

Pinpoint Tests

NOTE: Use Rotunda 73 Digital Multimeter 105-R0051 or equivalent when performing electrical pinpoint tests.

The fastest way to find a condition is to work with the tools that are available, which means working with proven diagnosis charts and the proper special tools for the system being worked on.

Refer to the following charts for performance testing procedures.

PINPOINT TEST A: INSUFFICIENT HEAT

A1 CHECK ENGINE COOLANT LEVEL

Allow engine cooling system to fully cool and check radiator coolant level.

Is coolant level low?

Yes	No
FILL and BLEED engine cooling system. REFER to Section 03-03. RETEST system.	GO to A2.

A2 CHECK HEATER HOSE ROUTING AND CONDITION

Check that heater water hoses are not crossed or routed incorrectly. Refer to Section 12-02 for heater hose routing.
Visually inspect condition of heater water hoses for pinched or collapsed conditions.

Are heater water hoses in good condition and routed properly?

Yes	No
GO to A3.	REPAIR or REPLACE heater water hoses as necessary. RETEST system.

A3 CHECK COOLANT FLOW THROUGH HEATER CORE

Start vehicle and allow to reach normal operating temperature.
Place temperature control knob in the full warm position.
Grasp inlet and outlet heater water hoses. Both heater water hoses should be warm to the touch due to coolant flowing through them.

Do heater water hoses indicate coolant flow?

Yes	No
GO to A4.	FLUSH heater core to remove obstructions. RETEST system. If flushing does not correct condition, REPLACE heater core. RETEST system.

A4 TEST THERMOSTAT

Start vehicle and allow to run for 10 minutes.
Feel the heater water hoses and the underside of the upper radiator hose.

Are the heater water hoses and the upper radiator hose cool?

Yes	No
REPLACE thermostat. RETEST system.	GO to A5.

A5 CHECK TEMPERATURE CONTROL DOOR OPERATION

Rotate temperature control knob from full warm to full cool and check temperature door for operation.

Does temperature door operate correctly?

Yes	No
CHECK for head gasket leaks. REFER to Section 03-00 for information on cylinder heads. REPAIR as necessary. RETEST system.	CHECK for binding, damaged or disconnected temperature door. REPAIR or REPLACE as necessary. RETEST system.

Vacuum Leak Diagnosis

The air handling system is designed to provide defrost when no vacuum is applied to any of the three air door vacuum motors. This is done to prevent a situation where defrost cannot be obtained due to a system vacuum leak. Instead, a leak in the vacuum control circuit will send all airflow to the defroster outlets. This condition may occur during acceleration (slow leak), may exist at all times (large leak) and may happen only when certain specific functions are selected, indicating a leak in that portion of the circuit.

The vacuum hoses used in the passenger compartment control circuit are constructed from PVC plastic material. The vacuum hoses used in the engine compartment are constructed of Hytrel. Because of the materials used, the vacuum hoses should never be pinched off during diagnosis to locate a leak. Use Rotunda Vacuum Tester 014-R1054 or equivalent to locate vacuum leaks. A wood golf tee can be used as a plug when it is necessary to plug one end of a vacuum hose for leak test purposes.

PINPOINT TEST B: DEFROST DOES NOT OPERATE

B1 CHECK SYSTEM AIRFLOW

With engine running and blower on high, check system airflow in each function selector position to determine which position(s) have incorrect airflow. Refer to vacuum application chart for correct system airflow.

Is airflow from the defroster outlets for all positions?

Yes	No
GO to B2.	GO to B13.

B2 CHECK VACUUM SUPPLY HOSE

Check vacuum supply hose to be sure it is connected to both the engine manifold and vacuum check valve.

Is hose disconnected?

Yes	No
RECONNECT hose. GO to B1.	GO to B3.

B3 CHECK VACUUM SUPPLY HOSE FOR LEAKS

Disconnect vacuum supply hose from engine manifold fitting and from check valve. Plug one end of hose and leak test with vacuum pump.

Does hose leak?

Yes	No
REPLACE or REPAIR as necessary. GO to B1.	CONNECT hose to manifold fitting. GO to B4.

B4 CHECK VACUUM CHECK VALVE

Check vacuum check valve for correct installation by removing the reservoir hose and the control assembly source hose (one at a time) from check valve and check for vacuum. Engine must be running for this test.

Is vacuum available at both check valve ports?

Yes	No
RECONNECT both hoses. GO to B6.	GO to B5.

B5 INSPECT VACUUM CHECK VALVE

Inspect vacuum check valve for an obstruction and/or proper operation. Airflow through the check valve should be in the direction toward engine (engine connection side is marked VAC).

Is check valve plugged or obstructed?

Yes	No
REPLACE check valve. GO to B1.	GO to B6.

B6 LEAK TEST VACUUM CHECK VALVE

Remove vacuum check valve from vehicle. Connect 2 hoses and a Tee fitting to outlet ports of check valve. Connect Rotunda Vacuum Tester 014-R1054 or equivalent to Tee fitting.

Pump 15 inches vacuum on check valve and observe gauge reading. If vacuum loss exceeds 1 inch per minute, remove check valve from tester and plug vacuum hoses. Pull a vacuum with the tester to be certain hoses and tester are not cause of leak.

If tester and hoses do not leak, check valve is cause of leak.

Does check valve lose more than 1 in. vacuum in one minute?

Yes	No
REPLACE check valve. GO to B1.	REINSTALL check valve and GO to B7.

B7 CHECK VACUUM RESERVOIR

Connect vacuum tester to vacuum reservoir and leak test reservoir. Reservoir must hold vacuum.

Does reservoir leak?

Yes	No
REPLACE reservoir. GO to B1.	CONNECT hose to reservoir. GO to B8.

B8 CHECK SUPPLY HOSE FOR LEAK

Disconnect and plug BLACK supply hose at control assembly. Disconnect other end of supply hose from check valve and leak test hose with vacuum tester.

Does supply hose leak?

Yes	No
REPAIR or REPLACE hose. GO to B1.	REMOVE plug and RECONNECT vacuum hose. GO to B9.

B9 CHECK CONTROL ASSEMBLY

Disconnect vacuum harness at in-line multiple connector near control. Plug all vacuum hoses except BLACK. Connect vacuum tester to BLACK hose. Select each function position, apply 15 in. vacuum and check for vacuum drop. Drop should not exceed 1 in. vacuum per minute for any function position.

Does drop exceed 1 in. vacuum per minute?

Yes	No
NOTE function positions where vacuum drops. GO to B10.	GO to B11.

B10 LEAK TEST CONTROL ASSEMBLY

Remove vacuum harness from control assembly. Connect vacuum tester to control supply port and plug control port that indicated a leak in Step B9. Select function positions noted in Step B9 and apply 15 in. vacuum after selecting each position. Vacuum drop should not exceed 1/2 inch per minute.

Does vacuum drop exceed 1/2 inch in one minute?

Yes	No
REPLACE control assembly. GO to B1.	GO to B12.

B11 CHECK SUPPLY HOSE

Disconnect BLACK supply hose from check valve. Connect vacuum tester to supply hose and operate tester as if pulling a vacuum. If tester can pull a vacuum, hose is plugged. If tester pulls a partial vacuum, hose is restricted.

Is hose plugged or restricted?

Yes	No
REPLACE supply hose. GO to B1.	GO to B15.

B12 LEAK TEST JUMPER VACUUM HARNESS

Plug one end of vacuum hose that indicated a leak in Step B9. Apply 15 in. vacuum to hose and observe vacuum gauge. Vacuum should not drop.

Does vacuum drop?

Yes	No
REPAIR and/or REPLACE vacuum jumper harness. GO to B1.	CHECK connection of vacuum harness to control assembly for leak. REPAIR as necessary. GO to B1.

B13 EVALUATE SYSTEM AIRFLOW

Is the airflow in Step B1 correct for each function position?

Yes	No
GO to B14.	GO to B15.

B14 ISOLATE LEAKING VACUUM CIRCUIT

Repeat step B1 and accelerate engine speed for each function position.

Does airflow go to defrost during acceleration?

Yes	No
GO to B19.	GO to B15.

B15 REVIEW VEHICLE HISTORY

Did system function properly prior to this complaint?

Yes	No
GO to B18.	GO to B16.

B16 CHECK VACUUM HOSES

Check each vacuum hose to be sure it is not plugged.

Is a hose plugged?

Yes	No
REPAIR or REPLACE as necessary. GO to B1.	GO to B17.

B17 CHECK VACUUM HARNESS

Compare vacuum hose colors in each vacuum harness to the vacuum schematic.

Do the hose colors agree with the schematic?

Yes	No
GO to B18.	REPLACE vacuum harness. GO to B1.

B18 CHECK VACUUM CIRCUIT

Check vacuum circuit for pinched or kinked vacuum hose.

Is hose pinched or kinked?

Yes	No
REPAIR as necessary. GO to B1.	GO to B19.

B19 CHECK VACUUM CIRCUIT CONNECTION

Check each vacuum hose connection to determine if it is partially connected or disconnected.

Is a vacuum hose connection disconnected or partially connected?

Yes	No
RECONNECT hose. GO to B1.	GO to B20.

B20 CHECK VACUUM HOSE

Disconnect both ends of vacuum hose in suspected circuit. Plug one end and leak test with vacuum tester.

Does vacuum hose leak?

Yes	No
REPAIR or REPLACE hose. GO to B1.	GO to B21.

B21 CHECK VACUUM MOTOR

Check vacuum motor for leaks with vacuum tester.

Does motor hold vacuum?

Yes	No
GO to B22.	REPLACE vacuum motor. GO to B1.

B22 CHECK VACUUM MOTOR INSTALLATION

Check attachment of vacuum motor arm to damper door.

Is motor arm attached to door or door crank arm?

Yes	No
CHECK for binding or damaged damper door. REPAIR as necessary. GO to B1.	CONNECT motor arm to door and/or crank arm and CHECK operation. GO to B1.

PINPOINT TEST C: INSUFFICIENT A/C COOLING

C1 CHECK A/C COMPRESSOR CLUTCH

Does the A/C clutch engage?

Yes	No
GO to C2.	REFER to Pinpoint Test G in this section.

C2 CHECK PRESSURE/CYCLE RATE

Use refrigerant system pressure/cycle and timing evaluation charts.

Hook up gauge set.
Set function lever at MAX A/C.
Set heater blower motor switch on HIGH.
Set temperature lever full cool.
Close doors and windows.
Use a thermometer to check temperature at the center discharge register. Record outside temperature.
Run engine at approximately 1500 rpm with A/C clutch engaged.
Stabilize with above conditions for 10-15 minutes with interior temperature between 21.1-26.7°C (70-80°F).

Check OFF/ON time of A/C clutch with watch. See Charts for normal cycle and timing rates.

Does A/C compressor cycle very rapidly?

Yes	No
GO to C4.	GO to C3.

C3 CHECK PRESSURES

Check system pressures.
Compare readings with normal system pressure ranges.

Does A/C compressor cycle within limits?

Yes	No
System OK. GO to C1.	GO to System Pressure and Cycle Timing Evaluation Charts and COMPARE observed pressures with chart. REFER to Refrigerant System Tests in the Service Procedures portion of this section. If A/C compressor cycles high or low: ON above 259 kPa (52 psi), OFF below 144 kPa (21 psi), GO toC4.

C4 CHECK FOR LEAKS

Leak check system.

Are there leaks in system?

Yes	No
SERVICE, LEAK TEST, EVACUATE and CHARGE system. System OK. GO toC1.	Low refrigerant charge or moisture in system. DISCHARGE, EVACUATE and CHARGE system.

PINPOINT TEST D: BLOWER MOTOR DOES NOT OPERATE

D1 CHECK BLOWER MOTOR OPERATION

Key to run.
Place function selector switch to FLOOR position and heater blower motor switch to HI position.

Does blower motor operate?

Yes	No
GO to D2.	GO to D4.

D2 CHECK BLOWER LO SPEED

Rotate heater blower motor switch to LO speed.

Does blower motor operate?

Yes	No
WIGGLE wires and CHECK for intermittent operation. REPAIR if necessary.	GO to D3.

D3 CHECK BLOWER MOTOR RESISTOR

Check resistor assembly for continuity of coils and thermal limiter.

Is resistor good?

Yes	No
CHECK Circuit 261 (O/BK) from blower motor to resistor and Circuit 57 (BK) from resistor to ground. REPAIR as necessary.	REPLACE resistor.

D4 CHECK BLOWER MOTOR

Key off.
Ground Circuit 261 (O/BK) at the blower motor. Position function selector switch to FLOOR position and turn key to run.

Does blower motor operate?

Yes	No
CHECK Circuit 261 (O/BK) between blower motor and the splice to heater blower motor switch and blower motor resistor for an open. REPAIR as necessary.	GO to D5.

D5 CHECK FUSE

Check blower motor fuse.

Is fuse good?

Yes	No
GO to D6.	GO to D9.

D6 CHECK FUNCTION SELECTOR SWITCH

Pull A/C control assembly from instrument panel enough to gain access to electrical connectors.
Turn function selector switch to FLOOR position and key to run.
Check for battery voltage at function selector switch Pin 3, Circuit 249 (DB/LG).

Are 12 or more volts available?

Yes	No
GO to D8.	GO to D7.

D7 CHECK SUPPLY VOLTAGE

Follow same conditions as Step D6.
Check for voltage at Pin 4, Circuit 181 (BR/O) of function selector switch.

Are 12 or more volts available?

Yes	No
TEST function selector switch for continuity in all switch positions. REPLACE switch if not continuous in all positions.	CHECK Circuit 181 (BR/O) between fuse and A/C control assembly.

D8 CHECK VOLTAGE

Reinstall the A/C control assembly.
Turn ignition key to RUN position and function selector switch to FLOOR position.
Check for battery voltage at blower motor Circuit 249 (DB/LG).

Are 12 or more volts available?

Yes	No
REPLACE blower motor.	REPAIR/REPLACE Circuit 249 (DB/LG) between A/C control assembly and blower motor.

D9 CHECK CIRCUIT

Key OFF.
Disconnect blower motor and install a new fuse.
Place function selector switch to FLOOR position and key to run.

Does fuse blow again?

Yes	No
GO to D10.	REPLACE blower motor.

D10 CHECK CIRCUIT FOR SHORT

Pull A/C control assembly from instrument panel enough to gain access to electrical connectors.
Disconnect wiring harness connector from function selector switch. Install new fuse and turn key to run.

Does fuse blow again?

Yes	No
CHECK Circuit 181 (BR/O) for short. REPAIR as necessary.	CHECK Circuit 249 (DB/LG) for short. REPAIR as necessary.

PINPOINT TEST E: NO OPERATION IN HIGH BLOWER SETTING

E1 CHECK BLOWER MOTOR OPERATION

Key to run, function selector knob to FLOOR and blower knob to first position from HI.

Does blower motor operate?

Yes	No
GO to E2.	GO to E4.

E2 CHECK BLOWER SPEED

Turn blower knob to HI.

Does blower motor operate on HI?

Yes	No
CYCLE heater blower motor switch from HI to LO several times. If blower operates each time, ADVISE owner of system operation. If blower does not operate in HI each time, REPLACE blower switch.	GO to E3.

E3 CHECK BLOWER SWITCH

Check continuity of blower switch.

TEST PROCEDURE
Switch Position	Continuity Between Terminals
Low	B
Medium 1	B + D
Medium 2	B + C + D
High	B + A + C

Is switch continuous in all positions?

Yes	No
SERVICE Circuit 57 (BK) between switch and ground. REPAIR as necessary.	REPLACE heater blower motor switch.

E4 CHECK BLOWER SPEEDS LO AND MEDIUM

Key to run and function selector knob at FLOOR, rotate blower knob to LO and then one position toward HI.

Does blower operate in both positions?

Yes	No
INSPECT harness connector at blower switch. REPLACE harness connector if damaged. If OK, REPLACE heater blower motor switch.	GO to E5.

E5 CHECK BLOWER SPEEDS

Reference blower motor speeds in Step E4.

Does blower motor operate in LO?

Yes	No
GO to E6.	REPLACE heater blower motor switch resistor assembly.

E6 CHECK BLOWER SWITCH CONNECTOR

Check to ensure connector is correctly and securely connected to blower switch.

Is connector properly attached to blower switch?

Yes	No
REPLACE heater blower motor switch.	RECONNECT and CHECK blower motor operation.

PINPOINT TEST F: BLOWER MOTOR OPERATES IN HIGH SPEED ONLY

F1 CHECK BLOWER OPERATION

Key to run, function selector knob to FLOOR and blower knob at LO.

Does blower motor operate?

Yes	No
GO to F5.	GO to F2.

F2 CHECK BLOWER SWITCH HIGH SPEED

Slowly move blower knob from LO to HI. Stop at each detent and check for blower operation.

Does blower motor operate in any speed except HI?

Yes	No
GO to F4.	GO to F3.

F3 CHECK GROUND CIRCUIT

Check Circuit 57 (BK) from heater blower motor switch resistor to ground for an open.

Is ground wire open?

Yes	No
REPAIR and/or REPLACE as required.	REPLACE heater blower motor switch resistor.

F4 CHECK CIRCUIT

Check Circuit 261 (O/BK wire) between blower motor and heater blower motor switch resistor for open.

Is circuit open?

Yes	No
REPAIR as necessary and CHECK blower motor operation.	REPLACE heater blower motor switch resistor.

F5 CHECK BLOWER SWITCH

Check blower motor operation several times in each blower knob position.

Does blower motor operate in all knob positions without interruption?

Yes	No
CHECK system operation in all function positions and blower speeds. If OK, INSTRUCT owner on correct operation of system.	GO to F6.

F6 CHECK BLOWER SWITCH CONTINUITY

Remove harness connector from blower switch and check continuity through switch in each position.

TEST PROCEDURE
Switch Position	Continuity Between Terminals
Low	B
Medium 1	B + D
Medium 2	B + C + D
High	B + A + C

Is switch continuous in all positions?

Yes	No
CHECK continuity of Circuit 754 (LG/W) and Circuit 752 (Y/R) between blower switch and resistor assembly. REPAIR as required.	REPLACE heater blower motor switch.

PINPOINT TEST G: A/C CLUTCH CYCLES RAPIDLY

G1 CHECK SYSTEM OPERATION

Set function selector lever at an A/C position.
Key to run.

Does A/C clutch engage?

Yes	No
Clutch circuit OK.	GO to G2.

G2 CHECK FOR VOLTAGE

Check for voltage at circuit wire at the A/C cycling switch.

Is voltage present?

Yes	No
GO to G3.	GO to G10.

G3 BYPASS A/C CLUTCH CYCLING PRESSURE SWITCH

Disconnect connector at A/C cycling switch.
Jumper connector pins.
A/C clutch should engage.

Does A/C clutch engage?

Yes	No
GO to G4.	GO to G7.

G4 CHECK HIGH PRESSURE CUT-OFF SWITCH FOR CONTINUITY

Place multimeter in the OHMS position.
Check A/C pressure cut-off switch for continuity.

Does A/C pressure cut-off switch test as having continuity?

Yes	No
GO to G5.	REPLACE A/C pressure cut-off switch. GO to G1.

G5 CHECK SYSTEM PRESSURE

Connect gauge set and check system pressure.

Is pressure above 379 kPa (55 psi) (ambient temperature above 10°C [50°F])?

Yes	No
REPLACE A/C cycling switch. Refer to Section 12-03A. GO to G6.	CHECK refrigerant system for leaks. REPAIR and CHARGE system as necessary. GO to G1.

G6 CHECK A/C COMPRESSOR PRESSURE RELIEF VALVE

Inspect area surrounding the A/C compressor pressure relief valve.

Are there signs of refrigerant venting (oily residue)?

Yes	No
REPLACE A/C compressor pressure relief valve. GO to G1.	CHECK A/C system for leaks. REPAIR as necessary (if no leaks detected, CHARGE system). GO to G1.

G7 CHECK VOLTAGE AT CLUTCH

Check for voltage at A/C clutch field coil.

Is voltage present?

Yes	No
GO to G8.	GO to G9.

G8 CHECK CLUTCH GROUND

Jumper ground terminal of A/C clutch field coil to ground.

Does A/C clutch engage?

Yes	No
SERVICE open in ground wire. GO to G1.	REPLACE A/C clutch field coil. REFER to Section 12-03B. GO to G1.

G9 CHECK FUSE

Does fuse have continuity?

Yes	No
GO to G10.	CHECK for short. SERVICE as necessary. REPLACE fuse. GO to G1.

G10 CHECK A/C CONTROLS

Move function selector lever to DEFROST position.
Check for voltage at Circuit 348 (LG/P) at the connector of A/C cycling switch.

Is voltage present?

Yes	No
GO to G12.	GO to G11.

G11 CHECK CIRCUIT 182 (BR/W)

Remove connector from control function selector switch.
Check for voltage at Circuit 182 (BR/W).

Is voltage present?

Yes	No
GO to G10.	CHECK for open in Circuit 182 (BR/W). SERVICE as necessary. GO to G1.

G12 CHECK A/C CONTROLS FOR CONTINUITY

Check A/C function switch for continuity.

Is there continuity through function switch only?

Yes	No
REPLACE A/C function switch. REFER to Section 12-03A. GO to G1.	CHECK for open in Circuit 348 (LG/P) between air conditioner control and A/C cycling switch. SERVICE as necessary. GO to G1.