Aerostar Van Heater Problem?

It sounds like you may be correct. There may be a blend door stuck or actuator malfunctioning. You may also have a vacuum leak because the doors are moved by actuators that use vacuum. Check the level of your coolant. If the coolant is to low then that could cause an insufficient heating problem. Also the heater control valve that delivers water to the heater core may not be working properly. You could have a freon leak that is causing the a/c to not cool down in the warm months like it should.

The coolant is easy to check. If you are not sure how to check it then check your owners manual. A copy of the manual is online if you need it at motorcraft.com. Next start the vehicle and let it run for a few seconds. Shut off the engine. Now rotate the the temperature knob from cool to hot. If the door that blends the warm & cool air is working you may be able to hear it moving. If not look under the hood at the hard vacuum lines. Some of them will run into the vehicle through the firewall. Those would be control lines for the blend door. Look behind the glove box while the vehicle is running and listen for a hiss. This would indicate a leaking vacuum line, loose line, or leaking actuator. Also the control head may be not working correctly.

If it is a actuator that is the problem that may be an easy fix. Vacuum lines can be tough. If a blend door is broken inside the a/c handler box the dash has to come out and the whole box needs replacing.

You may have more than one single problem. I know a/c / heat repairs can be expensive but if you find a trust worthy mechanic you will get what you pay for.

Hope this helps.