HVAC Problem
I've got a problem with the HVAC controls on my '99 E350. So far this is what I've got - air is only coming out of the defrost ducts, the temperature controls and fan speed controls work fine. The rear air is in defrost mode as well and only blows air out the floor vents only. I've got vacuum at the coupler up under the hood just before it enters the cabin area, but haven't taken the dash apart to chase it any further.
At this point, I'm thinking I've got a vacuum leak in the directional controls. Any advice or direction on where to look next? This is the one area on my vehicles that really frustrates me - it sounds so simple but rarely is.
Thanks!
CONDITIONS DETAILS/RESULTS/ACTIONS
A1 CHECK THE SYSTEM AIRFLOW
Start Engine
WARNING: Carbon monoxide is colorless, odorless and dangerous. If it is necessary to operate the engine (6007) with the vehicle in a closed area such as a garage, always use an exhaust collector to vent the exhaust gases outside of the closed area.
Start the engine.
Set the heater blower motor switch (18578) to HIGH.
Check the system airflow in each function position to determine which position(s) have incorrect airflow. Refer to the vacuum schematic in this section.
Is the airflow coming from the defroster nozzles in all of the positions?
Yes
GO to A2 .
No
GO to A14 .
A2 CHECK THE VACUUM SUPPLY HOSE
Check the vacuum supply hose to be sure that it is connected.
Is the hose disconnected?
Yes
RECONNECT the vacuum supply hose. RESTORE the vehicle. GO to A13 .
No
GO to A3 .
A3 LEAK CHECK THE VACUUM TANK AND HOSES
NOTE: The in-line vacuum harness connector is located in the vehicle, below the instrument panel, on the passenger side.
Intake Manifold Vacuum Hose
In-Line Vacuum Harness
Plug the vacuum supply hose at the intake manifold.
Carry out a vacuum leak test on the vacuum tank, check valve and hoses.
Connect the vacuum pump to the in-line connector.
Apply a vacuum.
Check for a vacuum leak.
Is there leakage?
Yes
GO to A4 .
No
GO to A9 .
A4 LEAK CHECK THE VACUUM SUPPLY HOSE
Remove the evaporator core housing; refer to Section 412-02 .
Vacuum Supply Hose
Carry out a vacuum leak test on the vacuum supply hose.
Plug one end of the hose.
Connect the vacuum pump to the other end.
Apply a vacuum.
Check for a vacuum leak.
Does the hose leak?
Yes
REPAIR or INSTALL a new vacuum supply hose. RESTORE the vehicle. TEST the system for normal operation.
No
GO to A5 .
A5 INSPECT THE VACUUM CHECK VALVE
Vacuum Check Valve
Inspect the A/C vacuum check valve (19A563) for any obstructions and correct operation. Airflow through the A/C vacuum check valve must be directed toward the engine.
Is the A/C vacuum check valve plugged or obstructed?
Yes
INSTALL a new A/C vacuum check valve. RESTORE the vehicle. TEST the system for normal operation.
No
GO to A6 .
A6 LEAK TEST THE VACUUM CHECK VALVE
Carry out a vacuum leak test on the A/C vacuum check valve.
Connect two hoses and a tee fitting to the outlet ports of the A/C vacuum check valve.
Connect the tee fitting to the vacuum pump.
Apply 51 kPa (15 in-Hg) of vacuum.
If the vacuum loss exceeds 3.37 kPa (1 in-Hg) per minute, then remove the A/C vacuum check valve and carry out a vacuum leak test on the vacuum pump.
Plug both of the hoses.
Apply a vacuum.
If the vacuum pump loses vacuum, then correct the problem and repeat this procedure.
Does the A/C vacuum check valve leak?
Yes
INSTALL a new A/C vacuum check valve, RESTORE the vehicle. TEST the system for normal operation.
No
GO to A7 .
A7 CHECK THE VACUUM RESERVOIR
Vacuum Reservoir
Carry out a vacuum leak test on the A/C vacuum reservoir tank and bracket (19A566).
Connect the vacuum pump to the A/C vacuum reservoir tank and bracket.
Apply a vacuum.
Check for a vacuum leak.
Does the A/C vacuum reservoir tank and bracket leak?
Yes
INSTALL a new A/C vacuum reservoir tank and bracket; refer to Section 412-04 . RESTORE the vehicle. TEST the system for normal operation.
No
GO to A8 .
A8 CHECK THE SUPPLY HOSE
Check the supply hose for a vacuum leak.
Connect the vacuum pump to one end of the supply hose.
Install a plug in the other end of the hose.
Apply a vacuum.
Check for a vacuum leak.
Disconnect the control assembly supply hose from the A/C control (19980) and the A/C vacuum check valve.
Check the supply hose for a restriction or blockage.
Remove the plug.
Apply a vacuum.
Check for a restriction or blockage.
Does the supply hose have a leak, restriction, or blockage?
Yes
REPAIR or INSTALL a new supply hose. RESTORE the vehicle. TEST the system for normal operation.
No
GO to A9 .
A9 CHECK THE CONTROL ASSEMBLY SUPPLY HOSE
A/C-Heater Function Selector Switch Supply Hose
Check the control assembly supply hose for a vacuum leak.
Connect the vacuum pump to one end of the control assembly supply hose.
Install a plug in the other end of the hose.
Apply a vacuum.
Check for a vacuum leak.
Check the control assembly supply hose for a restriction or blockage.
Remove the plug.
Apply a vacuum.
Check for a restriction or blockage.
Does the control assembly supply hose have a leak, restriction, or blockage?
Yes
REPAIR or INSTALL a new A/C-heater function selector switch supply hose. RESTORE the vehicle. TEST the system for normal operation.
No
GO to A10 .
A10 CHECK THE CONTROL ASSEMBLY
A/C-Heater Function Selector Switch Supply Hose
Vacuum Harness In-Line Multiple Connector
Carry out a vacuum leak test on each function position.
Plug all of the vacuum hoses except for the A/C-heater function selector switch supply hose.
Connect the vacuum pump to the A/C-heater function selector switch supply hose.
Set the A/C-heater function selector switch to a function position.
Apply 51 kPa (15 in-Hg) of vacuum.
Check for a vacuum drop exceeding 3.37 kPa (1 in-Hg) per minute.
Does the vacuum drop more than 3.37 kPa (1 in-Hg) per minute?
Yes
NOTE which function position(s) leak. GO to A11 .
No
GO to A15 .
A11 LEAK TEST THE CONTROL ASSEMBLY
A/C-Heater Function Selector Switch
Carry out a vacuum leak test on the A/C-heater function selector switch for the functions that were noted in Step A10.
Plug the leaking control port(s), as noted in Step A10.
Connect the vacuum pump to the A/C-heater function selector switch supply port.
Select the corresponding function position.
Apply 51 kPa (15 in-Hg) of vacuum.
Check for a vacuum drop exceeding 1.68 kPa (1/2 in-Hg) per minute.
Does the vacuum drop more than 1.68 kPa (1/2 in-Hg) per minute?
Yes
INSTALL a new A/C-heater function selector switch. RESTORE the vehicle. TEST the system for normal operation.
No
GO to A12 .
A12 LEAK TEST THE JUMPER VACUUM HARNESS
Vacuum Hose(s)
Disconnect the vacuum hose(s) that indicated a leak in Step A10 from the corresponding vacuum control motor.
Carry out a vacuum leak test on each of the hose(s).
Connect the vacuum pump to one end of the vacuum hose.
Install a plug in the other end of the hose.
Apply 51 kPa (15 in-Hg) of vacuum.
Check for a vacuum leak.
Do the vacuum hose(s) leak?
Yes
REPAIR or INSTALL a new vacuum hose harness (19C827). RESTORE the vehicle. TEST the system for normal operation.
No
CHECK the vacuum hose harness connection. REPAIR or INSTALL a new vacuum hose harness as necessary. RESTORE the vehicle. TEST the system for normal operation.
A13 EVALUATE THE SYSTEM AIRFLOW
Check the airflow that was noted in Step A1 for each function position.
Is the airflow in Step A1 correct for each function position?
Yes
GO to A14 .
No
GO to A15 .
A14 ISOLATE THE LEAKING VACUUM CIRCUIT
Start Engine
WARNING: Carbon monoxide is colorless, odorless and dangerous. If it is necessary to operate the engine with the vehicle in a closed area such as a garage, always use an exhaust collector to vent the exhaust gases outside of the closed area.
Start the engine.
Set the heater blower motor switch to HIGH.
Cycle the A/C-heater function selector switch to each function position during acceleration.
Check for a variation in the system airflow for each function position during acceleration.
Does the airflow go to defrost during engine acceleration?
Yes
GO to A19 .
No
GO to A15 .
A15 REVIEW THE VEHICLE HISTORY
Review the vehicle history to determine if the system operated correctly prior to the complaint.
Did the system operate correctly prior to this complaint?
Yes
GO to A18 .
No
GO to A16 .
A16 CHECK THE VACUUM HARNESS
Compare the colors on each vacuum hose to those shown on the vacuum schematic. Refer to the vacuum schematic in the Diagnosis and Testing portion of this section.
Do the vacuum hoses agree with what is shown on the vacuum schematic?
Yes
GO to A17 .
No
INSTALL a new vacuum hose harness. RESTORE the vehicle. TEST the system for normal operation.
A17 CHECK THE VACUUM CIRCUIT
Inspect each vacuum hose to determine if it is pinched or kinked.
Are any of the vacuum hoses pinched or kinked?
Yes
REPAIR the damaged vacuum hose(s) or INSTALL a new vacuum hose harness. RESTORE the vehicle. TEST the system for normal operation.
No
GO to A18 .
A18 CHECK THE VACUUM CIRCUIT CONNECTIONS
Check vacuum hose connections to determine if any are disconnected or partially connected.
Are any of the vacuum hoses disconnected or partially connected?
Yes
RECONNECT the vacuum hose(s). RESTORE the vehicle. TEST the system for normal operation.
No
GO to A19 .
A19 CHECK THE VACUUM HOSES
Vacuum Hose(s)
Disconnect each suspected vacuum hose from the system.
Carry out a vacuum leak test on each suspected hose.
Connect the vacuum pump to one end of the vacuum hose.
Install a plug in the other end of the hose.
Apply a vacuum.
Check for a vacuum leak.
Check each suspected hose for a restriction or blockage.
Remove the plug.
Apply a vacuum.
Check for a restriction or blockage.
Do any of the vacuum hose(s) have a leak, restriction, or blockage?
Yes
REPAIR the vacuum hose(s) or INSTALL a new vacuum hose harness. RESTORE the vehicle. TEST the system for normal operation.
No
GO to A20 .
A20 CHECK THE VACUUM MOTOR
Vacuum Control Motors
Disconnect the suspected vacuum control motor.
Carry out a vacuum leak test on each of the suspected vacuum control motor(s).
Connect the vacuum pump to the vacuum control motor (s).
Apply a vacuum.
Do any of the suspected vacuum control motor (s) leak?
Yes
INSTALL a new vacuum control motor (s). RESTORE the vehicle. TEST the system for normal operation.
No
GO to A21 .
A21 CHECK THE VACUUM MOTOR INSTALLATION
Check for correct attachment of the vacuum control motor arm to the damper door or damper door crank arm.
Is the vacuum motor arm correctly attached to the damper door or damper door crank arm?
Yes
CHECK for a binding or damaged damper door. REPAIR or INSTALL a new damper door as necessary. RESTORE the vehicle. TEST the system for normal operation.
No
CONNECT the vacuum motor arm to the damper door or damper door crank arm. CHECK the damper door operation. RESTORE the vehicle. TEST the system for normal operation.
Somehow the connection to the vacuum reservoir has broken - behind the evaporator housing.

I've installed a new reservoir under the hood and will finish running a new line to the selector switch in the morning.
I do believe that the dampers now work better than before the failure. Thanks for the input guys. It turned out to be far simpler than I had feared it would be.

CAME ACROSS YOUR POST AND FOLLOWED IT WILL BE FOLLOWING THE RECOMMENDED PROCEDURE.
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