I was driving my 2000 Pontiac Montana with my heater on then all of a sudden it stop blowing hot air. Only cold air would come out of the vents.

Check your flapper doors and blower/ducts for clogs or problems.
Also the cooling system thermostat could be stuck open. Auto heaters have a tiny radiator heater core that uses hot engine coolant to warm the cabin air.
That all has to be working in order to get heat.

heater blows cold air idle chrysler 300 Questions & Answers ...

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Find solutions to your heater blows cold air idle chrysler 300 question. ... blow warmair for a few mins then back to luke warm. i replaced thermostat ... HEAT BLOWSCOLD AIR WHEN IDLING ONLY GETS HOT WHEN START DRIVING ... About 15 minutes after driving the diver side vents start blowing straight cold air but the ...

Heater only works when pressing the gas? - DoItYourself.com ...

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Nov 3, 2011 - When I press the gas, the air from the vents is nice and hot. .... So am Idriving a car with a ton of problems, or could the power steering ... Just anotherquestion, when warmed up does the engine temperature ... When the heater is on and I'm not pressing the gas pedal, luke warm air blows from the vents.

Heater blows cool air when stopped and warm air while ...

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RedditFeb 12, 2014 - Heater blows cool air when stopped and warm air while driving 2008 Kia Spectra (self. ... just fine but appears to blow cool air when I was stopped at a stoplight. ... My temp gauge would also be pegged high when at idle / low RPM. ...thermostat only blocks coolant going to the radiator, and the heater core, ...Missing: 300m ‎luke

Why is My Car AC Blowing Hot Air? - BlueDevil Products

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Is your heater blower motor working on all speeds ? Are you get any air coming from the rear vents ?

Hard to read your question, do you mean it blows cold air out of the front vents and hot air out of the rear passenger vents?

If the air coming out of the front is just cool and not cold, and the rear vents are warm, you have low freon and need to have it serviced.

it sounds like the heater core is stopped up and the hot air can not blow thru

sounds like it might be a little low on freon and/or might need the cabin air filter replaced,try replacing the cabin air filter first,its located behind the glove box,hope this helps

We have the same problem. It's an air pocket in the cooling system. The cause can be anywhere from not filling the system all the way or most likely a leak has developed and air has entered into the system as the coolnt level has dropped. The coolant light goes off and on as the air pocket moves around.

Our Montana has a leaky intake gasket, which is the source of the problem. A very common problem with the 3.4. It should go for another 100K plus though, once it is repaired.

That is correct, the air blend door actuator. "flapper valve" may need to be replaced or cleaned and free from binding up. Good luck and hope this helps. If there is an Auto Zone in your area, they can order the part you need and give you the step by step instructions to removing the old actuator and replacing it if it's damaged. Good luck and keep me posted, be glad to help. 

Vacuum line has to be connected to this system in order for it to work properly.

There is a mix damper inside your duct that controls the heat over heater core and ac evaporator that to your floor and one to your defrost. it is probable an electric actuator, that is not functioning properly. If yu can locate it and manually move it, you might have to remove the actuator motor first, you should be able to figure out your problem, I hope this helps! merry Christmas!