1993 Ford Aerostar Luke wam heat through vents

I recently had the heat problem fixed but the only thing now is when im accelerating up a hill or step into the gas the heat blows from the vents and diverts to the defrost. What causes that to happen?

I wasnt getting heat because the heater core gasket wasnt installed, got that taken care of but like I said. Now im getting all kinds of heat but it diverts to the defroster when going up a hill or stepping into passing gear.

The upper return hose should always be checked for clogs before you re install it, mine was so clogged I could not get it cleared out without pulling it 100 percent straight off

Yeah the upper and lower hoses are hot. Must be a vacuum problem why it diverts from heater to defrost upon acceleration

Check for a vacuum leak first, transmission has a vacuum solenoid on it right by the muffler shield. The cruise control, brake booster, fuel pressure regulator(on left side of fuel rail just below the fuel pressure (schrader) test orifice), the pvc as well as the dashboard selector itself (is a vacuum actuator) devices the rear heater box on xl models(behind panel right behind driver seat) has a flap door that moves, you can see its elbow pointing backwards almost behind the unit to the left side of the unit about mid high and you should see it move as you adjust the heat selector, (floor is best heat output available from rear) the vacuum line also controls the water shut off valve right under the vehicle over there each are vacuum controlled devices

Im sorry but im not understanding what your saying. Is what your saying about why the heat diverts?

It could divert if there was a major vacuum leak somewhere toilet plunger, leak the motor would not idle good drive the van after you get under the transmission and disconnect/pull test/plug/retest the vacuum solenoid on it to see if that is your problem, the manifold vacuum or may be getting oil in it from the transmission.

Are you talking the motor on heater or the engine motor to the van. Cause the engine does idle rough sitting at idle. Does it have something to do with the transmission?

What year is your torque converter? It may hold too much oil for the transmission to be able to pump up enough oil pressure into it. Take out the thermostat and see if you have more torque without it