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Volkswagen: Heater, vw vento, coolant water

QUESTION: the heater inside the car is always cold I have a VW Vento 1993

ANSWER: Christina,
 There is a valve inline with the 1 inch diameter supply "heater hose", in the engine compartment, which allows hot water from the radiator to enter the heater core inside the car.  It works like a valve on a faucet which has a lever, rather than a screw knob.  This is controlled by the dashboard knob, via a cable behind it, sort of like the brakes on a bicycle.  The connection point of the cable at the control knob, or to the under hood valve, often made of plastic, can be broken or disconnected either end.  
 I am assuming the fan is working, which can be another cause, in which case may be only a fuse.
- Rick

---------- FOLLOW-UP ----------

QUESTION: My dad and I got behind the dashboard and saw that the cables were working ok when we moved the dials, but we cant find the valve in the heater hose, could you explain where exactly this is, I have a VW Vento Saloon 93, the Fan is working and blows cold air all the time, its very slightly warm when the car has been running but not enough to warm the car or defrost windows.  Thank you

  From inside the engine compartment, you should see the two 1" hoses exiting the firewall from the passenger compartment.  These hoses are connected from the heater core (inside the dash) to the engine; one is the supply line, which is normally connected on or near the water pump, and other one is the return line connected to the engine block or head somewhere.  If you follow these hoses from the firewall towards the engine connection points, at some point you should run into the valve in question (attached picture) inline with one of the hoses.  It splits one hose in half in order to interrupt flow of hot engine coolant water, which must normally flow in a complete loop to provide heat.  Attached to it will have the other end of the control cable (which you saw from behind the dash board) which controls a lever and therefore how much the valve is opened.  Have one person look under the hood at the control valve lever as another moves the temperature control back and forth from inside the car.  You may find the cable or lever has become disconnected or somehow broken, etc.
 If the lever seems to be working fine, but there is still no hot air, there must be a blockage in the lines.  There could possibly be chunks of rust which have lodged inside the heater core lines(the smallest point in the system.)  The system will need to be back flushed, but be careful not to use too much water pressure for fear of bursting the heater core lines(no high pressure washers.)  Many auto parts stores sell kits to DIY cooling system flush, with required adapters and instructions, for using your home water hose.

- Rick