It should be right above the water heater on the cold side. It is either a straight lever that is a quarter turn type or a round handle that screws in. If it is the straight lever one, you probably pull down on it to shut it off, but it can be put in either way and you may have to push it up. Look at where it attaches to the valve and you can see the stops and which way to turn it.
Please see link below.
this model does not have a heater control valve, it has a specail thermostat that controls flow.
Need more info here. Not sure what a heater pump is.
its right beside the wiper switch
To locate the main water valve in your home, look for a valve typically located near the water meter, usually in the basement, crawl space, or near the water heater. It is usually a lever or wheel that can be turned to shut off the water supply to your entire house.
Look near or behind the alternator. The valve that controls flow of coolant to the heater core on my 1987 Aerostar is located on the left wall of the engine compartment. I imagine the 1991 is similar. Trace the heater hoses from the engine/water pump and you will find it.
To locate the water shut off in your home, look for a valve near the main water line where it enters your house. This valve is typically located in the basement, crawl space, or near the water heater. Turn the valve clockwise to shut off the water supply to your home.
Check if the water supply line valve underneath the sink is on or off .."On" will be turning counterclockwise ,If not look for the hot water heater and make sure the water supply valve is turned on.
The heater valve is in line in the heater hose from the top back of the 350 engine about half way to where it enters the firewall to connect to the heater core. The valve has a steel wire control cable connected to the top of the valve control lever. It has two hose connections, one in from the engine and one out to the firewall core entry point. Trace your heater hoses and look for the metal valve with the spiral covered control wire.
The water shut off valve in your home is typically located near the water meter, usually in the basement, crawl space, or near the water heater. It may also be found outside your home, near the foundation. Look for a lever or wheel that can be turned to shut off the water supply to your home.
It should be fine if you move it yourself. It should not mess anything up by you touching it, and not a repair man.
The heater control valve on a GMC Savana van with a 305 engine is typically located in the engine compartment, along the heater hose that connects the engine to the heater core. It is usually mounted on or near the firewall, making it accessible for maintenance. To confirm its exact position, refer to the vehicle’s service manual or look for a valve that controls the flow of coolant to the heater core.