My 95 sunfire air condition will not blow air out the air condition vents.just put new heater core in vehicle.it was working before.

Most cars today do not have a water diversion valve for the heater core; rather they use a blend door in the ducting under the dash. There are a pair of them. One door diverts input air either through the heater core or the A/C evaporator, or both. This will control temperature. The other door diverts air to the floor vents, dash vents, or the defroster vents. These doors are vacuum-controlled on most models. You could have a door problem, or possibly a clogged heater core. To check the heater core, run the vehicle to operating temperature, and then trace the heater hoses to where they enter the firewall. Check each hose for temperature. The inlet hose should be very warm to the touch, and the outlet one the same or slightly cooler. If the outlet hose is much cooler than the input, there is probably a restriction in the heater core.

Replace the bad thermostat you bought.

check the heater core

I woild be checking the vent controls as if the ac is working and the core was blocked then the air would be cool when the heat was selected but not changing Fixing the heater has resulted in a /c not being good enough to cool the air if the vent is not properly selecting. The point is that if the vent selection is not working properly (vacuum hoses) then the 2 faults will be related.

It blows cold air with the mode selector in what position. If it is on defrost and you have the temp adjusted to full heat than the a/c will be on to dry the air before it hits the windshield, this helps to remove the fog from the windows. If there is no heat coming out the vents than you need to check to make sure the blend door is working. You should hear a distinctly different sound out the vents when you turn the heat from full cold to full hot. Also check to see if the heater core is plugged. With the engine warm you should be able to feel little difference in the temp of the two hoses that go to the heater core. If one is hot and one is cool than there is a flow issue. Either the water control valve is bad, it is not being opened by the HVAC control head, the is a vacuum leak to the control valve or the heater core is plugged. Your vehicle may or may not have a valve that controls the flow of hot water to the heater core.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

With blower on high and tempature to max heat check to see if you have good air flow in all mode selections (defrost, vent, floor etc.). If so and you still have no heat then check heater core hose going from engine to inside car to heater core with vehicle running and coolant tempature about half on guage. If both hoses are hot and coolant in radiator/overflow bottle is full then hot cold blend door is stuck in cold position. If coolant level is low you will get no heat, check coolant level first.

Replacing the heater core in a Pontiac Sunfire is a very difficult and complex process. The heater core is kept within the car's heating/air conditioning module behind the instrument panel. So many other parts have to be drained and removed from the car to reach the heating/air conditioning unit that you may be better off leaving this to a professional mechanic--especially one licensed to work on air conditioning units.
Things You'll Need:

• Wrench
• Container
• Air conditioning reclaimer
• Hose clamp pliers
• Screwdrivers
• Heater core
• R134a refrigerant
• Recharge service hose

1. Removing the Core
   • Make sure the car is cool, the front wheels are facing forward and the ignition switch is off. Drain the engine coolant by removing the drain plug at the radiator and letting the coolant pour into a clean container, then do the same at the engine block's drain plug. Recover the refrigerant by connecting an air conditioning reclaimer to the system high and low side fittings as its instructions state.
   • Disconnect the evaporator lines to the evaporator by removing its bolt and disconnect the heater hoses from the core by loosening the hose clamps with clamp pliers. Remove the drain tube from the evaporator case. Disconnect the negative battery cable.
     
   • Remove all the trim covers and panels from the instrument panel; some of these are screwed on and some require a flat bladed tool. Remove all air distribution ducts from the panel, the air bags, the steering wheel, the radio, the tilt and washer levers and all electrical connectors, then unscrew and remove the instrument panel from the car. Unbolt the cross vehicle beam, remove its wiring harness and remove the beam.
     
   • Remove the air outlet in the floor. Disconnect the wiring harness for the heater/air conditioner and the electrical connectors at the blower's motor and resistor.
     
   • Remove the heater/air conditioning module by removing its attaching bolts and the assembly screw. Remove the heater cover case by removing its heat stakes and screws and remove the heater core.
     
2. • Install the replacement core into the heater/air conditioner module, then re-connect the heater core cover case. Install the assembly in the vehicle, aligning the mounting bracket to the front of the dash slot and mounting bolt hole. Reconnect the electrical connectors and wiring harness and install the floor air outlet.
     
   • Reinstall the cross vehicle beam and every component of the instrument panel. Reconnect the negative battery cable.
     
   • Install the drain tube back on the evaporator case. Connect the hater hoses and the evaporator lines.
     
   • Recharge the air conditioner. Connect a can of R134a refrigerant to the air conditioner's low side service fitting with a recharge service hose and a high pressure gauge to the high side fitting. Open the service hose valve while the car runs with the A/C at the max and let the vapor flow until the gauge reads between 225 and 250 PSI.
     
   • Refill the cooling system at the radiator filler neck. Use fresh coolant if the old liquid is dirty in any way
     

see my post re overheating for new jetta,just vent the top heater hose pipe of air,the clip closest to the engine.when engine is running and hot(WEAR RUBBER GLOVES,ITS HOT)

replace the cabin air filters

Steam coming through the air vents indicates a leak in heater core. The heater core is like a small radiator that is used to heat the inside of your car in the winter time. The blower, blows air through the heater core and into the inside of the vehicle. The steam you are seeing is the hot coolant leaking from the core.

- Jim