Heating / heater issues 2003 sonoma

Most cars today do not have a water diversion valve for the heater core; rather they use a blend door in the ducting under the dash. There are a pair of them. One door diverts input air either through the heater core or the A/C evaporator, or both. This will control temperature. The other door diverts air to the floor vents, dash vents, or the defroster vents. These doors are vacuum-controlled on most models. You could have a door problem, or possibly a clogged heater core. To check the heater core, run the vehicle to operating temperature, and then trace the heater hoses to where they enter the firewall. Check each hose for temperature. The inlet hose should be very warm to the touch, and the outlet one the same or slightly cooler. If the outlet hose is much cooler than the input, there is probably a restriction in the heater core.

if heat is coming out then one of your vent diverters has stuck shut. this usually happens because you never run the heat over the summer. look under your dash and see if the vents for the heater are open. those are the easiest to see. use wd-40 to lube all the contact points where the door opens and closes. there are other diverters further into the system but you have to take the dash off to get to those in most cases. not too difficult on the Impala but get help if you do not know how to do this.

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Possibly plugged or inerporable heater core. Possibly heater core valve (this diverts hot air through your heater system) When you flushed the block, was there a lot of contaminant? 95% of the time, cold heat means thermostat. Also there are a lot of really cheap after market thermostats, you can buy one as low as $6.00. That being said, just because a thermo is new doesn't necessarily mean it opens/shuts when it should. You can look on You Tube on how to test one in your kitchen with boiling water,.

So three basic things affect interior heat temps. Thermostat, plugged heater core/.valve, and insufficient coolant or liquid to tranfser heat. If your interior coolant (engine temp) is working normally and your vehicle reaches operating tempature according to the needle, your thermosat is probably not the cause.

My bet is somehow, your heater core is plugged so that their is not enough "flow"

If both heater hoses are getting hot and the radiator is full of coolant, you may have a problem with one of the blend doors under the dash.
The blend doors direct air thru the heater core and the vents.

You are correct. That is the common cause of no heat if the water pump and therm are still good. The plastic door is most likely stripped.

Check that the two hoses of the heater core at the firewall are getting hot. If both are not hot, then the heater core is plugged up. Try to flush in this case to free up sediment. If that doesn't work, maybe a new heater core is required, assuming that the blend door is operating correctly, and diverting hot air to the defrost or front vents.

If the heater coil was bad, it would be leaking radiator fluid... probably into your dash/floorboard (depending on where it is installed in your model car). There is a switch that diverts the hot radiator fluid through the heater coil when you want heat. There is also an air diverter valve that helps to mix the hot and cold air. The fluid valve is controlled by the A/C settings control. The one that you use to choose between heater/air conditioner/vent/ defrost. The air diverter is controlled by the temp mixing controller. The most simple explanation is that one of those valves or the controller of one of those valves is not working. If the hot water cant be diverted through the heater coil, the coil can't exchange the heat (warming the air). If the air diverter (hot/cold controller) cant move to add heat, then all you will feel is air from the vent side (from outside) or from the A/C cooling the air.

I would guess that its either a controller or one of the valves themselves. Odds are, it is a controller. That tends to be what malfunctions first.

Is this a 4.3 V6 or a 2.2 4 cyl. ? You may have a blown head gasket. What is the temp gauge showing ?

The controls for your heater/vent selection is inside the dash, behind the control switches you use to select the vents the heat/AC will come out.
When you move the selection levers, there's a few things that happen. Vacuum is applied to the doors (which are inside) and they open or they work using cables to move the doors or both. The different doors open, directing air flow to the vents selected.
Remove the controls from the dash (which should just be removing some screws, maybe a few small pieces of dash and pulling it out). The controls will be connected inside so they will not come out very far.
Just check to see if anything is disconnected and try operateing the controls with the heat on to see how they work.
Sometimes they just stick or the doors stick. This system is the way the 1991 models worked but since they are the exact same, it should be this way also.
Look it up in some sort of repair manual for more info. I find with these trucks, they don't heat very well using the front vents anyway. I find using the bottom vents work best for heat unless you need defrost.
The "heater" selection will atomatically use the bottom vents, "bi-level" AC will use the front and bottom vents if I remember right and regular AC will automatically use the front vents. For the trouble in removing these controls (the whole dash would need to be removed for repair) I probably would just live with the way they work if they do work atleast properly (enough heat and AC). If you find that you don't get enough heat or AC when in use, check the cooling system for proper operation and blockages/mineral buildup and check the AC system incase it needs recharging or you have leaks.

sound like heater box has issues. doies the heater box have trash in it, like leaves???? It might be a vacuum line dry rottering and making the dampher not work properally. I need to be there to really check it out??????