My problem is my heater wont heat... it blows cold air all summer and winter. have heard there is a vacuum hose that controls a flap that lets heat into the car from the engine, and if vacuum is not hooked up, or leaking, it wont open that flap, there fore, not blowing any heat into the car. is this true, and if so, where is this flap located?

You have one of two problems. The heater core is plugged /
restricted or there is an inoperative internal blend door motor problem. Start the vehicle and let it reach operating temperature. Feel the hoses under the hood that go into the heater core. They should be close to the same temperature. If one is hot and the other luke warm/cold.... the heater core is plugged/restricted. If both hoses are near the same temperature, suspect a defective/non operational blend door motor that controls heat/cold/airflow attached to the heater box assembly

I need more info. When you set the vent control to defrost does it direct the air to the windshield. and when you set it to floor does it go there. if yes the control to divert air is working. before replacing the control unit you need to find the lines that feed hot water to the heater and check to see if line coming in to the heater is hot and the line returning from the heater is warm to hot. sometime the heater gets plug. if so just disconnect the lines to the heater and flow water from your garden hose to the return line of the heater for about a minute or so this will flush dirt from the heater. reattach the lines and check for heat. This is a known problem for all cars as they get old.

check that the heater control (tap ) is being turned on by the controls.. Have an accredited ac mechanic check the ac system .

Sounds like it's the air control flap which determines the mix of heated and fresh air. This could be vacuum controlled or manually with a cable.

hi Planeman.
Why is the heater in my car not working? Ken Mattson, owner of Len's Automotive in Bellevue, Wash., says a car heater can stop working for a number of reasons, including: A low antifreeze/water level in the radiator due to a leak in the cooling system. A bad thermostat that isn't allowing the engine to properly warm up.11 Dec 2013

Why Isn't My Car Heater Working? ' Angie's List

https://www.angieslist.com/articles/why-isnt-my-car-heater-working.htm Search for: Why is the heater in my car not working?
Why is my car heater not blowing hot air?Hot coolant from the engine passes through a heater core, which looks and functions a lot like a small radiator, and a blower motor forces air through it. ... It's also the reason that a plugged heater core, stuck thermostat, or air in the cooling system can all cause a car's heater to blow cold.9 Jul 2017When Your Car Heater Blows Cold Air - Lifewirehttps://www.lifewire.com/when-your-heater-blows-cold-air-534667
How do you fix the heat in your car?Begin with the vehicle on level ground, engine off (cold) in park with the emergency brake set.Heater Controls. Step 1 - A heater cannot operate unless the engine is full of coolant/antifreeze. ...Refilling Cooling System. ...Engine Thermostat. ...Blend Door Actuator. ...Broken Vacuum Line. ...Heater Control Valve. ...Vacuum Gauge. ...Heater Core.How to Fix a Car Heater in Under 30 Minutes - 2CarPros
What are the symptoms of a bad thermostat?A motor with a bad thermostat will run fine for the first few minutes, then overheatrapidly. Other symptoms include the engine and radiator making a rumbling, gurgling, boiling sound: like a steam pipe knock, if you've ever heard one of those. A thermostat sticking open can make your heater not work in the winter.Auto, Car, Truck THERMOSTAT Repair bad thermostat symptoms
or go to this link if you need more help.
2008 ford ranger has heater that won get hot Google Search

Unless you have symptoms of over-heating, I rather doubt that your water pump is a problem. I recall that my water pump had a metal impeller (1992 C900); I haven't heard of a plastic impeller on a Saab pump before. (Most pump failures are the bearing seal, and the pump leaks coolant) If your temp gauge is slightly low (and was OK before) I'd rule out water pump issues.

You might have one or more of the following issues:

1. did you use a Saab thermostat? The Saab stat has three stages (no flow to rad - cold; flow to rad and heater core - normal operation; and no flow to heater core, full flow to rad - overheating) that most after market stats don't.
2. did you use a low temp stat? this opens at about 82 deg (rather than 89 deg), and will run cooler during the winter, hence you gauge will show lower than the mid point. The big benefit is that your engine won't overheat during the summer (a very good thing!) with the low temp stat.
3. has your rad and heater core been flushed recently? If the heater core is obstructed flow will be reduced and the heater will run cool. Feel the rad and heater hoses when your engine is warm; if heater hose is much cooler than rad hose with heater temp set to max, then core flow is likely restricted, or valve is not moving much from the shut position.
4. is you vacuum tank properly connected and are there no leaks in the vacuum piping? The tank is in the driver side rear wheel well below the trunk deck on a convertible, and in the passenger side front fender area on the other cars. It's a white bottle with one or two hoses connected to it. If not properly on, your vacuum operated heater flaps won't move. Does the air distribution knob make sucking or hissing noises when you set it to different positions? If not, check the tank connections, look for vacuum line leaks, then suspect the vacuum valve behind the distribution knob.
5. Lastly, the shaft connecting the temp control knob to the valve behind it may not be properly in place. This can be inspected, and adjusted if necessary, from the speaker/vent cutout on top of the dash. Make sure you re-connect the black flex hose to the air vent tube, or you'll get no defrosting afterwards!
6. remember, the centre vents always blow cold air; a brilliant idea from Saab so the driver (and passenger) can get fresh air in the face and stay awake while the rest of the driver, passenger and car is toasty!
7. see http://townsendimports.com/Web/cooling_system_folder/thermostatreplacement.htm for flushing and stat replacement info
   

that switch controls a vacuum operated door that lets a/c or heat thru.when accelerating,the vacuum in the engine changes so it sound like a vacuum issue.take apart the center stack and there is a vacuum actuator in there connected to the flap door .i have seen those have issues with the metal tab broken away from the plastic that moves it.is the a/c piping cold under the hood where it goes into the heater a/c assembly?the compressor should be cycling on and off and the pressure tested.

The heater valve on these cars are hard to access. If you are trying to get rid of the heat, a quick solution is putting a valve on the heater hose from the outside. Cut the hose and install a valve in which you can regulate the amout of hot coolant going into the heater core. Since its summer you might as well shut the valve once installed. Winter time comes just open them up again.

Yeah Ron, the flap that covers the heater core is open and when you're moving the air is pushed over the heater core and into the cab your in. Possibly just a vacuum line of that controls said flap. Check all vacuum lines for good proper connection to these flaps because all of them are vacuum actuated.

i have a ford fiesta 51 plate,when i turn on heater i only have cold air the thermostat has been fixed and coolant levels are ok heatin hoses are all hot,but inside the car its still blowing cold