the vents control sometimes just quits so i got no air blowing through vents
fan working fine on all speeds
i took part of the dash apart and i noticed that its controlled by vacuum
is there a vacuum pump somewhere ??
thank you

 

there is a vacuum pump that shares a common shaft with the power steering pump I believe. . .but what it sounds like is you have a leak on that particular line.

 

On diesel engines, the vacuum check valve is integral to the engine vacuum pump nipple and is threaded into the vacuum pump.

VACUUM CHECK VALVE
On models with a gasoline engine, a vacuum check valve is installed in the accessory vacuum supply line near the vacuum tap on the right side of the engine intake manifold. On models with a diesel engine, a vacuum check valve is installed on the engine vacuum pump. The vacuum check valve is designed to allow vacuum to flow in only one direction through the accessory vacuum supply circuits.
The use of a vacuum check valve helps to maintain the system vacuum needed to retain the selected heater-A/C mode and vehicle speed control settings. On gasoline engine models, it prevents the engine from bleeding down system vacuum through the intake manifold during extended heavy engine load (low engine vacuum) operation. On diesel engine models, it prevents oil from contaminating the vacuum supply system by maintaining vacuum in the pump after engine shut-off.


VACUUM PUMP
The vacuum pump and the power steering pump are combined into a single assembly on diesel engine models Diesel Vacuum & Power Steering Pump Assembly Both pumps are operated by a drive gear attached to the vacuum pump shaft. The shaft gear is driven by the camshaft gear.
The vacuum pump is a constant displacement, vane-type pump. Vacuum is generated by four vanes mounted in the pump rotor. The rotor is located in the pump housing and is pressed onto the pump shaft.
The vacuum and steering pumps are operated by a single drive gear pressed onto the vacuum pump shaft. The drive gear is operated by the engine camshaft gear.
The vacuum and power steering pump shafts are connected by a coupling. Each pump shaft has an adapter with drive lugs that engage in the coupling.
The vacuum pump rotating components are lubricated by engine oil. Lubricating oil is supplied to the pump through an oil line at the underside of the pump housing.
The complete assembly must be removed in order to service either pump. However, the power steering pump can be removed and serviced separately when necessary
The vacuum pump is not a serviceable component. If diagnosis indicates a pump malfunction, the pump must be replaced as an assembly. Do not disassemble or attempt to repair the pump.
The combined vacuum and steering pump assembly must be removed for access to either pump. However, the vacuum pump can be removed without having to disassemble the power steering pump.
If the power steering pump requires service, simply remove the assembly and separate the two pumps. Refer to the pump removal and installation procedures in this section.
VACUUM PUMP OPERATION
Vacuum pump output is transmitted to the HEVAC, speed control, and EGR systems through a supply hose. The hose is connected to an outlet port on the pump housing and uses an in-line check valve to retain system vacuum when vehicle is not running.
Pump output ranges from a minimum of 8.5 to 25 inches vacuum.
The pump rotor and vanes are rotated by the pump drive gear. The drive gear is operated by the camshaft gear.

 

Mine had the same problem. It was caused by the vaccum line along the fire wall collapsing at a point where it was spliced.