Heater blowing out cold air

Feel the two heater hoses once the engine is warmed up. They should be too hot to hold onto for very long. If they are just warm, and the radiator hoses are hot, suspect the heater core is plugged, usually from early formulas of Dexcool that tended to cause clogging. That can usually be cleared by running water through from a garden hose. If the heater hoses are hot, suspect a problem with the temperature door or its actuator on the heater box. If you have an automatic temperature control that uses a computer module, those cause a lot of trouble too.
If the heater core is plugged, you may want to back flush the entire cooling system to keep it from plugging up again

See the guide below

https://www.2carpros.com/articles/coolant-flush-and-refill-all-cars

With the engine at full operating temp, locate the 2 heater hoses where they go into the firewall and feel them to see if they are both too hot to hold. If they are.

The heat in that vehicle is controlled by a blend door that regulates heated air flow. It is operated by a vacuum motor/actuator. The problem can be that the actuator itself could be bad, a problem with the vacuum control head or vacuum supply or the door itself could be damaged. This is what needs to be determined by examining the actuator and see if it is responding to heat change commands or not.

Hi:
Start by removing the control assembly. It is either run by a cable or vacuum. Check to make sure nothing is discinnected.

Let me know what you find.

Joe

Your best shot is just replace the thermostat and try flushing out the heater core both ways and see what happens-also check the heater control valve and the air blend door-

Ther are a few possibilities;

The heater vent door is not operating. It is controlled by cable and runs from the heater control to the heater box. Check to see if it has come off its clasp. If it has turn heat all the way up so cable extends all the way out and puch the vent door in same direction. Connect end and put cable in clasp/holder.

The other possibility is that the heater core valve is not working. There are 2 hoses that rung to the firewal for the heatercore. One of them will have a valve on it and a cable which turns the valve open/close. Sometimes they come loose at the clamp and have to be retightened. The valve can also get stuck and the cable will not move it. In that case you need to replace the valve.

It could be your water pump, but if your car isn't overheating, then that's unlikely.

It could be your heater control valve, a clogged heater core, or air in your system.

Sounds like you should flush out your heater core directly at it and flush it good, the heater core may even be bad or the blend door is not forcing enough air through the heater core.

Try flushing it and if equipped with a heater control valve inline to the heater core make sure it moves freely, if not its plugged up.

Just because you've had the system flushed, doesn't mean there isn't a blockage in your heater core.

Your engine has what we call a "reverse flow" coolant system. I won't bore you with the technical details. But what this means is, if your heater core is NOT blocked, and your thermostat is functioning correctly, then you either have a malfunctioning water pump, or you are getting air in your system.

Because you have a reverse flow system, when air gets in the system, it collects inside of the heater core and stops the coolant from flowing through it. (That's how you get your heat) A quick way to check to see if this is the case: When your engine is fully warm, turn on your heater and place the controls on the hottest option with the fan blower on high. Then rev the motor to at least 1500 r.P.M.'S. If the air becomes hot while you are reving the motor, then that's proof air is in the system.

If that doesn't work, then it's probably your water pump. However, if it is you water pump, then your engine should frequently over heat. Which makes me believe it's air in the system.

And unfortunately, if it's air, then that means you have a blown head gasket. (Expensive)

Finally, to check if you have air in the system:
Take off the cap to either the radiator or the surge tank. Look inside while someone revs the motor to at least 1500 r.P.M.'S. If you see air bubbles in the antifreeze, you definitely have air in the system. (Blown head gasket)