Check behind the heat control panel to be sure that the vacuum hoses are all securely plugged into the control switch. As a safety measure on all cars, if you lose vacuum altogether, the default position for air direction is on defrost, so you can always see out of the windshield. Jake McCahn

The water is not circulating through the heater core or you have a control problem. If the heater is putting out heat then it is probably a control problem. If no heat then - water pump out, low on coolant, or maybe the therostat is stuck open.

Thermostat stuck open, if older car possibly clogged heater core- when run at oper temp the hoses going into/out of heater core be sure one is very hot - start with thermostat $$$ cheap & easier than a heater core problem!

Where the air blows out control are vacuum operated.A more common problem is when the air is stuck on defrost only.The cause is essentially the same, so check out the "Related Question" below for where to go next

1. heat control linkage disconnected or broken or vacuum source problems(low vaccum source or broken vacuum lines) 2. heater unit doors stuck or non functioning heater door actuators

If you have already tried adjusting the temp controls the problem is likely a defrost control that is stuck in the "On" position. It is operated by the same timer as the ice maker. This is not a do-it-yourself repair.

The heater control valve is used to shut off hot coolant from entering the core when the heater is in the off position. A heater control valve can be actuated by either a vacuum line or a cable from the vacuum heater control valve to the heater core. This hose should be warm; if not the heater control valve is stuck and needs to be replaced

Could this be 2 separate problems?Stuck in defrost modeNo heatSee "Related Questions" below for more about both

Little or no heat from heater/defrost if t-stat is stuck open. Engine overheats if t-stat is stuck closed.

It sounds like your air flow diverter is stuck on defrost. Basically it is a little door that diverts the air fom vent to defrost to feet. It could be either the heater control valve, or te temperature selecter cable is broke.

The HVAC doors that control the airflow are activated by small vacuum motors. The system is designed to fail safe; this means that the system will fail in full defrost mode. So, knowing this and the fact that you have heater but no A/C or defrost you should assume the system has a failed control head (the part that you select functions with with button or lever). Or the doors are stuck due to an warped duct system (usually high heat related).

Could be a vacuum leak "defrost" is the default position of the system Check vacuum lines and motors under the dash

Thermostat is missing or stuck open, coolant level is low, heater core is plugged or heater control valve is stuck closed.

Could be,a stuck open thermostat,low on coolant,plugged heater core,faulty temp blend door actuator,

Your air mix door is stuck, follow the cable from the temp control to the heater/ac unit and see if the flapper is moving, if not the door itself may be stuck or broken and you'll need to get in there and replace it.

The heater control valve is stuck open.

The blower resistor power module has failed. It is behind the glove box.

There are several possible causes. A thermostat stuck open A heater control valve stuck closed A malfunctioning blend air door (located in the heater box) Low coolant level Malfunctioning heater controls

Thermostat stuck open or heater core clogged. Bad radiator cap or small hole in cooling system.

Thermostat stuck open. Heater core clogged. Heater temperture control valve defective. Low on coolant.

not function how. No heat, not enough, no fan doesnt' change heat to defrost? All different answers. No heat, not enough, May just be low on coolant. Therostat stuck open. No fan, fuse, ground, switch. Doesn't change heat/defrost? Cable, control, some switches are vacumn operated.

Thermostat stuck open, heater core clogged, or the heater temperture control vlalve is defective.

By heater element I am assuming you mean a heater core. If that is the case then you have one of two problems. Either the thermostat is stuck open and needs replacing or the heater temperature control valve is defective.

If it's stuck in defrost your battery died and messed up the computer. Disconnect battery for 5 or more min. It worked on my 96

Heater control valve stuck open. Possible blend air door failure.