Nothing coming from vents with a new blower installed

Sounds like you either need a new blower motor that's inside the dash, or a new AC compressor.

Either you have a blower motor FUSE that has gone bad "typically the problem" or you have a burned out blower motor. Usually the cause of a blown or burnt motor if not a Fuse, Is caused by the vented air from outside letting debris like sticks or leaves,acorns etc. enter the fan box. If ANY of the mentioned items get caught in the "blower box" then it will usually blow the fuse and or burn up the blower motor. Start in your fuse box and look for a burnt fuse and replace with same size fuse. If it blows the new fuse quickly then you have debris in "Blower box" that will have to be removed before adding yet another fuse. I have had the same problem and I found a bunch of leaves in my "Blower Box". I removed the leaves and replaced the burned out fuse. And I have had no more problems with the blower motor blowing air.

Fuses would be the first thing to check. Then the switch and then the blower motor. If you have power to the motor and it isn't doing anything. You'll have to replace it.

If the problem is a lack of air flow from the vents, and you suspect the blower motor is not running at times, you would need to test the blower relay and blower motor for power and ground when it is not working.

I'd have to say it's the blower motor. Does it blow hot air when the heater is on?

It sounds like you have a vacuum leak. When there is no vacuum present to acutate the system, it will default to air only coming from the defrost vents. Is the blower motor operating or is the 'no air' you're talking about just no air blowing? If it's not blowing, check your fuse; if that's good, check for voltage at the blower connection. If you have voltage at the connection, remove the resistor to make sure it isn't bad befor condemning the blower motor.

check blower moter relay or fuse ..if ok probly the control switch fan blower control switch....

The blower motor is either bad, or if you hear it blowing in the front but nothing comes out of the vents, then it's a vacuum motor problem. The flaps aren't angled right to allow air to come out of the vents (either for a/c, heat, or defrost).

It's less than foot from the heater core. I would guess that either the damper doors are not on correctly or the vent hoses are not hooked up. Can you hear the blower motor running? Maybe they didn't hook the motor back up when they replaced the heater core. It takes a ground and a hot wire.I can't remember where it's at but it may be part of the same unit. Did you check the fuse?