1996 Bronco/F-Series

Section 12-03A: Air Conditioning System, Manual A/C-Heater

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

DIAGNOSIS AND TESTING

Pinpoint Tests

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 control motors (18A318). 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 (small 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 of polyvinyl-chloride (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 Leak 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 A: IMPROPER AIRFLOW FROM OUTLETS

A1 CHECK SYSTEM AIRFLOW

Start engine and place heater blower motor switch in HIGH position.
Check system airflow in each function selector setting to determine which position(s) have incorrect airflow.

Is airflow from the defroster outlets for all function selector settings?

Yes	No
GO to A2.	GO to A13.

A2 CHECK VACUUM SUPPLY HOSE

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

Is hose disconnected?

Yes	No
RECONNECT hose. RETEST system.	GO to A3.

A3 CHECK VACUUM SUPPLY HOSE FOR LEAKS

Disconnect vacuum supply hose from engine manifold fitting and from A/C vacuum check valve.
Plug one end of hose and leak test with vacuum tester.

Does hose leak?

Yes	No
REPAIR or REPLACE as necessary. RETEST system.	CONNECT hose to manifold fitting. GO to A4.

A4 TEST VACUUM CHECK VALVE

Test A/C vacuum check valve for correct installation by removing the reservoir hose and the control assembly source hose (one at a time) from the A/C vacuum 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 A6.	GO to A5.

A5 INSPECT VACUUM CHECK VALVE

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

Is A/C vacuum check valve plugged or obstructed?

Yes	No
REPLACE A/C vacuum check valve. RETEST system.	GO to A6.

A6 LEAK TEST VACUUM CHECK VALVE

Remove A/C vacuum check valve from vehicle.
Connect two hoses and a tee-fitting to outlet ports of A/C vacuum check valve.
Connect vacuum tester to tee-fitting.

Pump 50.5 kPa (15 inches) vacuum on the A/C vacuum check valve and observe vacuum tester gauge reading. If vacuum loss exceeds 3 kPa (1 inch) per minute, remove A/C vacuum 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, A/C vacuum check valve is cause of problem.

Does A/C vacuum check valve lose more than 3 kPa (1 inch) vacuum in one minute?

Yes	No
REPLACE A/C vacuum check valve. RETEST system.	REINSTALL A/C vacuum check valve. GO to A7.

A7 CHECK VACUUM RESERVOIR

Connect vacuum tester to A/C vacuum reservoir tank and bracket.
Pull a vacuum on the reservoir and observe gauge reading. Reservoir must hold a vacuum.

Does A/C vacuum reservoir tank and bracket leak?

Yes	No
REPLACE A/C vacuum reservoir tank and bracket. RETEST system.	CONNECT hose to A/C vacuum reservoir tank and bracket. GO to A8.

A8 CHECK SUPPLY HOSE FOR LEAK

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

Does supply hose leak?

Yes	No
REPAIR or REPLACE hose as necessary. RETEST system.	REMOVE plug and RECONNECT vacuum hose. GO to A9.

A9 CHECK CONTROL ASSEMBLY

Disconnect A/C plenum vacuum harness at in-line multiple connector near A/C control.
Plug all vacuum hoses except BLACK.
Connect vacuum tester to BLACK hose.
Select each function position, apply 50.5 kPa (15 inches) vacuum and check for vacuum drop. Vacuum drop should not exceed 3 kPa (1 inch) vacuum per minute for any function position.

Does vacuum drop exceed 3 kPa (1 inch) vacuum per minute?

Yes	No
NOTE function position(s) where vacuum drop occurs. GO to A10.	GO to A11.

A10 LEAK TEST CONTROL ASSEMBLY

Remove A/C plenum vacuum harness from A/C control.
Connect vacuum tester to control assembly supply port which indicated a leak in step A9.
Select function position(s) noted in step A9 and apply 50.5 kPa (15 inches) vacuum after selecting each function position. Vacuum drop should not exceed 2 kPa (1/2 inch) per minute.

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

Yes	No
REPLACE function control switch. RETEST system.	GO to A12.

A11 CHECK SUPPLY HOSE

Disconnect BLACK supply hose from A/C vacuum 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. RETEST system.	GO to A15.

A12 LEAK TEST JUMPER HARNESS

Plug one end of vacuum hose that indicated a leak in step A9.
Apply 50.5 kPa (15 inches) vacuum to hose and observe vacuum gauge reading. Vacuum should not drop.

Does vacuum drop?

Yes	No
REPAIR or REPLACE vacuum jumper harness as necessary. RETEST system.	CHECK connection of vacuum harness to A/C control for leak. REPAIR as necessary. RETEST system.

A13 EVALUATE SYSTEM

Repeat steps in test A1.

Is airflow in step A1 correct for each function position?

Yes	No
GO to A14.	GO to A15.

A14 ISOLATE LEAKING VACUUM CIRCUIT

Repeat step A1 and accelerate engine speed for each function position.

Does airflow go to defrost during acceleration?

Yes	No
GO to A19.	GO to A15.

A15 REVIEW VEHICLE HISTORY

Check vehicle service records for past service reports.

Did system function properly prior to this complaint?

Yes	No
GO to A18.	GO to A16.

A16 CHECK VACUUM HOSES

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

Is hose plugged?

Yes	No
REPAIR or REPLACE as necessary. RETEST system.	GO to A17.

A17 CHECK VACUUM HARNESS

Check to be sure that all vacuum hoses are correctly color coded.

Are the vacuum hoses correctly color coded?

Yes	No
GO to A18.	REPLACE vacuum harness.

A18 CHECK VACUUM CIRCUIT

Check vacuum circuit for pinched or kinked vacuum hose(s).

Is a hose pinched or kinked?

Yes	No
REPAIR or REPLACE as necessary. RETEST system.	GO to A19.

A19 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. RETEST system.	GO to A20.

A20 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 as necessary. RETEST system.	GO to A21.

A21 CHECK VACUUM CONTROL MOTOR

Check vacuum control motor for leaks with vacuum tester.

Does vacuum control motor hold vacuum?

Yes	No
GO to A22.	REPLACE vacuum control motor. RETEST system.

A22 CHECK VACUUM CONTROL MOTOR INSTALLATION

Check attachment of vacuum control motor 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. RETEST system.	CONNECT vacuum control motor arm to door and/or crank arm and CHECK operation. RETEST system.

PINPOINT TEST B: HEATER DOES NOT CHANGE TEMPERATURE

B1 CHECK COOLANT LEVEL

CAUTION: Engine should be fully cool before removing radiator cap. If the engine and cooling system are not fully cool, use extreme caution when removing radiator cap. Excess pressure within the radiator can result in hot coolant and steam escaping from the radiator with enough force to injure or scald persons standing near the vehicle when the radiator cap is removed. Use a shop towel around the radiator cap when opening the radiator cap. Turn the radiator cap only to the first release point. Step back and allow system pressure to release before fully opening the radiator. When system pressure has been completely released, remove radiator cap with shop towel still wrapped around the radiator cap.

Remove radiator cap and check coolant level.

Is coolant level in the radiator low?

Yes	No
REFILL radiator with coolant to proper level. RETEST system.	GO to B2.

B2 CHECK THERMOSTAT

Start engine and allow to run at least 10 minutes.
Carefully open radiator cap and observe coolant for evidence of circulation. Slightly increase engine idle speed if necessary.

Does coolant show evidence of circulation?

Yes	No
GO to B3.	REPLACE thermostat. RETEST system.

B3 CHECK HEATER HOSES

Check heater water hoses for kinks.
Check that heater water hoses are not crossed.

Are heater water hoses kinked or incorrectly routed?

Yes	No
REPAIR or REPLACE as necessary. RETEST system.	GO to B4.

B4 CHECK FOR HEATING SYSTEM BLOCKAGES

Start engine and allow to reach normal operating temperature.
Feel heater water hoses.

Do both heater water hoses become too hot to hold?

Yes	No
GO to B5.	If both heater water hoses become too hot to hold, GO to B5. If only one heater water hose becomes too hot to hold, a blockage is indicated. CHECK heater water hoses for obstructions. REPAIR or REPLACE as necessary. RETEST system. If heater water hoses check as OK, blockage is in the heater core. FLUSH engine cooling system. If flushing does not clear blockage, REPLACE heater core. RETEST system.

B5 CHECK TEMPERATURE CONTROL DOOR OPERATION

Rotate temperature control knob from the full cool position to the full warm position and check operation of the temperature control door.

Does the temperature control door operate correctly?

Yes	No
CHECK drive belt for proper tension or signs of slippage and wear. REPAIR or REPLACE as necessary. RETEST system.	CHECK temperature control door for a binding condition. Also CHECK the A/C temperature cable for connection to the temperature control door and A/C control. REPAIR or REPLACE as necessary. RETEST system.