No heat coming out of windshield defrost vent .no blowin air

Defrost blend air door may be failing due to vacuum leak, bad check valve or bad actuator.

Put the defroster on and move your temp setting towards warm and youll feel it come out of there. Heat doesn't come through those vents on normal heater setting those are the defroster vents.

You do not mention the type of car you have. If you have air that blows out the defroster and panel vents you should have defrost. Do you smell a sweet odor coming from the car? This could be antifreeze leaking though the heater core. This will cause your windshield to remain foggy.

Mode Door 1.
a.This door regulates air flow to either the dash vents or defrost/floor. If you have air flowing only through the vents with no defrost or floor, this door is failing. From our experience, this door is usually the first domino to fail. Not sure why, just is.
<!--[if !supportLists]-->4.Mode Door 2.
a.When mode door 1 is set to divert air away from the vents and into the second stage of the system, door #2 chooses whether air goes to the defrost vents to the windshield or out through the floor vents in the passenger and driver's side footwells. Failure is indicated by an inability to choose between defrost and floor.
b.This door turns out to be the most difficult to replace. In order to replace the door, the dash panel has to be removed. It's still better than the dealer fix because you don't have to evacuate the AC system, drain the radiator, and remove the plenum box. But it is more work than the other fixes. When this door breaks, it falls in the down position, blocking the floor vents and diverting all air through the defrost vents. From a safety standpoint, this is good since you'd most likely rather have a clear windshield than warm feet. We suspect that a large percentage of customers will just leave this door unrepaired. You will have heat through the dash vents and to the windshield, just nothing to the floor. It's inconvenient, but you'll have to make the determination if warm feet are worth the extra work to fix the door. An extra pair of socks is easier.

sounds like the doors that open and close that direct the air are jammed, or are not receiving a signal. Have someone run a code check which should tell you. May just need to have a faulty code erased or...$$$ repair by Volvo.

ur heater core no good need to replace the heater core

Check the actuator motor and rods on the heater box inside. The motor moves the doors in the heater to direct the heat to the area you request. It is a small motor on the driver side or in front of the heater above the dash.

you may have abad slector door acuator.which is alittle motor bolted on the heater box.It move a door in box to direct air flow to right location.hope this helps.

the deflector flap that move to direct air flow is stuck under the dash.

The vent flap foam lining has come loose and needs to be removed or reglued . A spray on contact adhesive works best , don't glue the flap to the vent casing.