Engine runs at normal temperature, heater blows cold air, why?

-Thermostat is not control the heater. It control only temperature in the engine.
-If you have no heater then check the following:
Make sure engine is cold before perform check.
-Check radiator is full of water or not. If not then fill it up
and try run like normal and turn on the heater.
-If now you have heat then you're done.
-But still no heat yet then cheek:
The heater valve. Is it open properly when you switch to hot or cold? If yes then NOT THE VALVE. Next lose both heater hoses from the engine and flush with garden water hose from one end and the other until you see water come out either end. Now connect back to the engine and top of the radiator more water.
You should be good to go now.

Good luck and stay warm

Mai

there are two hoses running to the heater radiator from the engine cooling system , one has a inline tap that controls the flow of hot water to the heater , check the tap is open , may be the control cable is not opening the tap , or it frozen and must be replaced.

Check if the engine temperature gauge indicates a normal reading. If it's normal, your heater core may be blocked, or the temperature control mechanism controlling the flap allowing the hot air is not working. If you can open up the hood and find the two hoses leading to the passenger compartment, see if they're both hot to the touch. If they are, then the doors are not moving properly diverting the air through the heater core. If it's cold then the core is probably blocked and may need replacement.

Top up Fluid level in over flow tank and radiator ( when cold ). Run engine to normall operating temperature and check for heater blowing hot air.Good starting point.

heater control valve

First you have to identify what causes the problem.
To do this you have to:
1) When engine is cold check the level of coolant. If it is low fill it up.
2) Start engine and check if engine reaches regular temperature. If your engine is not heated enough it means your thermostat does not work properly and should be replaced.
3) If engine temperature is normal, then check the temperature of pipes that go to/from heater core. These pipes are located up the fire wall (easier access is from the passenger side). If pipe/pipes are cold (even engine is worm) it means you heater core is plugged and should be flushed. Keep in mind, flushing the whole cooling system is different from flushing heater core.
4) If pipe/pipes are hot/warm, turn off the fan, switch controller to the hot position, wait for 3-4 minutes and turn on the fan. Note if the cold air blows first or warm air blows first but it cools down in 5-10 seconds. If the air blows cold than it is most probably the problem with blend door or blend door actuator.
5) If air blows warm first and then cools down, then while running engine and remaining the transmission in PARKING position, press on the gas pedal until your engine reaches 3,000 RPM. Check if your heater blows warm/hot air. If it does, then your water pump does not work properly and should be replaced. If the air still cold, I would suggest to flush the heater core.

It is most probably the problem with blend door or blend door actuator. But just in case I would suggest to follow the entire procedure:

First you have to identify what causes the problem.
To do this you have to:
1) When engine is cold check the level of coolant. If it is low fill it up.
2) Start engine and check if engine reaches regular temperature. If your engine is not heated enough it means your thermostat does not work properly and should be replaced
3) If engine temperature is normal, then check the temperature of pipes that go to/from heater core. These pipes are located up the fire wall (easier access is from the passenger side). If pipe/pipes are cold (even engine is warm) it means you heater core is plugged and should be flushed. Keep in mind, flushing the whole cooling system is different from flushing heater core.
4) If pipe/pipes are hot/warm, turn off the fan, switch controller to the hot position, wait for 3-4 minutes and turn on the fan. Note if the cold air blows first or warm air blows first but it cools down in 5-10 seconds. If the air blows cold than it is most probably the problem with blend door or blend door actuator.
5) If air blows warm first and then cools down, then while running engine and remaining the transmission in PARKING position, press on the gas pedal until your engine reaches 3,000 RPM. Check if your heater blows warm/hot air. If it does, then your water pump does not work properly and should be replaced. If the air still cold, I would suggest flushing the heater core.

First you have to identify what causes the problem.
To do this you have to:
1) When engine is cold check the level of coolant. If it is low fill it up.
2) Start engine and check if engine reaches regular temperature. If your engine is not heated enough it means your thermostat does not work properly and should be replaced.
3) If engine temperature is normal, then check the temperature of pipes that go to/from heater core. These pipes are located up the fire wall (easier access is from the passenger side). If pipe/pipes are cold (even engine is warm) it means you heater core is plugged and should be flushed. Keep in mind, flushing the whole cooling system is different from flushing heater core.
4) If pipe/pipes are hot/warm, turn off the fan, switch controller to the hot position, wait for 3-4 minutes and turn on the fan. Note if the cold air blows first or warm air blows first but it cools down in 5-10 seconds. If the air blows cold than it is most probably the problem with blend door or blend door actuator.
5) If air blows warm first and then cools down, then while running engine and remaining the transmission in PARKING position, press on the gas pedal until your engine reaches 3,000 RPM. Check if your heater blows warm/hot air. If it does, then your water pump does not work properly and should be replaced. If the air still cold, I would suggest flushing the heater core.

Do this when cool. Take radiator cap off, start the engine, turn on heat (not defrost) and now top up coolant to about an inch or 2 from top of radiator, as level drops down, and let vehicle run until the radiator fan comes on, then off, about 3 times, and add coolant as needed while it's running. After that, put radiator cap back on tight & make sure return bottle is filled to proper level. Now try that & see how heat is, temperature gauge etc, and keep an eye on return bottle level for a while. Let me know how it is.

Start with cold engine. Make sure coolant is topped up, leave cap off & run heater while engine running, to be sure all air is bled out of system. Feel hoses going in & out of firewall to heater core. That should be close to same temperature (by feel) . If big difference in temperature to touch, then either a valve in the line is closed or restricted, or heater core may be plugged. Also check if revving engine a bit increases heat temperature at all inside.