My heat does not work in my car. but the ac does. what could be the problem?

actuator is not working on the blend door. It is not responding to the command when you select either heat or ac on the passenger side. The temperature blend door actuator is not moving to supply either heat or ac.

Sounds like high blower relay is bad

there is a blower relay circuit board located right by the blower motor which sounds like your problem to me i've worked on several that had the same type problem and thats what it was. the two blower motor wires will plug into it and there are two screws that hold it on

vent flap shutting off?

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

If you are talking about the belt for the ac compressor, yes the heater should still work.
If the blower is not working, you will need to have the blower motor checked for voltage and ground.

The AC sheds the heat from the passenger compartment through the condenser (which looks like a second radiator), which is in front of the engine's radiator. That “preheats” the air that pulls heat from that radiator.

If the radiator has all it can do to shed the engine's heat using the air that is at ambient temperature, preheating that air will push it over the line into overheating.

Additionally, the AC removes the heat in the passenger compartment through the work that the AC compressor does. The AC compressor gets that power to do that work from the engine. This in turn causes the engine to work harder, creating more heat to get rid of than when the AC is off.

If the coolant is old, replace it.
Ensure the belt is tight enough on the water pump.
On many cars there is an electri fan that comes on with the AC, mounted in front of the condenser. If you have this, ensure it is operating.

The control for the AC/Heater door isn't working. To have AC the door has to close so that the hot air is not being blown into the car. When this door is closed it allows the cool air to pass through. This is either controled by vacuum or a ele. switch

I had similar problem on my 2001 Insight. Had to replace some cooling system hoses eaten by rodents... Works like a champ again.

It's just a fuse...I have a 93 es300 and my heat/ac just went out one day. I found it was just a fuse from the one's next to the stearing coloum.