No air/heat coming through vents

There's a chance that the actuator motor has either failed, or it's nylon gear has worn out. You will have to pull it out and inspect.

Thermostat -stuck open

Check if happening at specific settings on the fan. Fans use resisters to slow down their speed. Typically the lowest setting will mess up before the highest. If coming a going means you change the speed and it goes away.

If it doesn't matter what speed, there is probably something in your vents. Do you park outside? Mice love getting into warm cars on cold nights, and build nests... a nice comfy place can be in vents...

Or have very small kids... mine used to love putting things in the vents and have them disappear! Could be cherios

sounds like the air mix rod is out of adjustment or if vacuum controled, its leaking can you hear a noise in the vehicle or can you find a vacuum hose off in the engine bay hope it gives a little help

First check the fuses if applicable, check for power to the switch (fan speed) access the resister, and inspect, or pull the fan (blower) motor and bench test it

the air distribution switch controls the air distribution and the fan, distribution switch in the 0 (straight down position) will be off. Car movement forces air into teh body, but with teh fan off there will be no air when the car stops. Does the fan run when the distribution switch is in any other position? it should respond to the speed settings of the fan switch.

There is a vacuum bottle accumulator that assists the distribution switch, sometimes this gets disconnected and the switch settings don't work.

Do you hear any noises if you turn the distribution knob while the car is running? suction noises, or flaps opening?

If not, then you likely have a vacuum problem (check for a white bottle in left front wheel housing, except convertible -> under the spare wheel, tank should have one or two vacuum lines connected to it (one for convertible). A disconnected or leaky line is the most likely cause.

Possible other causes are faulty air distribution switch; burned out fan motor; inoperative vacuum solenoid motors controlling air distribution flaps.

But check the vacuum accumulator first, if under the spare wheel, the lines are easily dislodged.

Common issue. Your air ducts were not reassembled properly and so the blower fan is working but the air is going out wherever the air duct is improperly fitted. Also the fan gate ( a metal gate that is used to block off any heat entering the system when you have the a/c on may be stuck in the close position. Whatever the case it can be repaired by getting in the sysem under the passenger side of the underside of the dash. You may want a professional mechanic to perform thid because it is a bit of a job to access all of the items needed. Hope this helps!!!

I may have had a similar problem, for a long time my blower motor made a loud howling/roaring noise, hard to explain, but I only heard the noise when the blower was turned on. It continued to blow air for a couple years then just quit, the noise it made continued for another 6 months to a year without air-flow. Finally it quit blowing air at all. I eventually replaced the blower motor and no more noise and air flow was restored. Hopefully you already have fixed this because removing and replacing the blower motor wasn't fun.

There may be some kind of obstruction in the duct work. Or, there may be a vacuum leak in the small tubes that operate the diverter that "tells" the warm air where to go. Have you checked to see if the air flow is coming out the floor vents?

You most likely have an air pocket in the cooling system. The heater core on these vans is much higher than the engine and they can be tough to get all the air out of them.

Make sure the coolant in the radiator is full when engine is cold- also fill the overflow bottle to the top. Chock the rear wheels. Jack up the front of the van as far as you can and support with jack stands. Run the engine until it's warm and then hold the RPMS at 2000 for about 5 minutes while checking for heat inside the cabin. You may hear some funny noises like something is trying to come through the firewall forcefully! That's the air pocket moving... you might not hear this also. Once you have good heat inside, let the engine idle- if the air coming form the vents cools off after a couple minutes, the air is still there- keep doing this until the air is hot coming from the vents at idle for more than a couple minutes. Once you have good heat, turn the engine off and let the engine cool completely- at least a couple hours... you will most likely see the level in the overflow drop dramatically. Lower vehicle and make sure overflow is at COLD FULL mark.

Newer Altimas also had a similar situation in which heat would go away at idle- usually not a problem with an air pocket, but Nissan has a bulletin out on putting the correct concentration of coolant/water in the system- these cars are very sensitive to changes in coolant mixture concentration.

Nissan Scope Technician- 10 years with Nissan