Blowing hot air after adding coolant - 2003 GMC Envoy

It sounds like your thermostat is stuck closed. Your thermostat also acts as a heater valve to let hot coolant go to your heater core to blow hot air if your thermstat is stuck close it prevents your coolant to run through your radiator to cool down and to blow hot air from your heater core. A way to check to see if your thermostat is working while its at operating temp feel the bottom and top radiator hose if your lower hose is cold and top is hot your thermo is stuck closed but be careful hoses might be very hot

first I would look under the hood with the a/c on to see if the compressor clutch is working, if not it could be a simple fix by adding refrigerant, if you have a leak then, you need to take it in and have a test performed on it, most shops have a dye that they put in to see where the leak is

My first thought was low coolant, but with the added point about the ac I'm leaning toward a blend door problem under the dash.

What engine 2.2 or 2.4 ?
Important: On vehicles equipped with the 2.4L engine, open the coolant air bleed valve. The coolant air bleed valve is located on the top of the thermostat bypass pipe/heater pipe assembly. Close the valve once a continuous stream of coolant is expelled from the valve.
Does the cooling fan come on ?
Notice: When adding coolant, it is important that you use GM Goodwrench DEX-COOL™ coolant. If coolant other than DEX-COOL™ is added to the system, the engine coolant will require change sooner: at 50 000 km (30,000 miles) or 24 months.
Close the radiator drain ****. Remove the drain hose.
If previously removed, install the engine block drain plugs.
When installing the drain plugs, use pipe sealer GM P/N 12346004.
Important: On vehicles equipped with the 2.4L engine, open the coolant air bleed valve. The coolant air bleed valve is located on the top of the thermostat bypass pipe/heater pipe assembly. Close the valve once a continuous stream of coolant is expelled from the valve.
Fill the surge tank to the base of the filler neck.
Start the engine with the pressure cap off. Let the engine run until the upper radiator hose starts to get hot.
If the coolant level in the surge tank is low, add the proper mix of coolant until the level reaches the full cold line.
Important: After servicing the cooling system, and if the vehicle is equipped with an intermittent low coolant light, an occasional low coolant light may be encountered during some extreme driving maneuvers. This complaint should be eliminated by removing the surge tank cap and adding coolant to a level just at or above the full cold line when the system is cold.
Install the cap onto the tank with hand tight pressure.

When the coolant flush was done, did you have the thermostat changed as well? I would have the thermostat replaced. If the temperature gauge was reading properly, but you still had warm, not hot air, it would lean more towards the heater core being clogged, but that deosn't seem to be the issue your having, so i would go with the thermostat replacement. And whereever you have the repairs done at...make sure they fully bleed all the air out of the cooling system, this could also cause poor warm-up / heating problems. Hope this helps...

Hi, there are several reasons your vehicle may be blowing hot air through the vents, such as a need to recharge refrigerant. There could also be a problem with the air conditioner's compressor. Vents will blow hot air if the compressor does not activate when the A/C is turned on. There may be an obstruction in the system, or the blend air door inside the HVAC unit may be stuck in the HEAT position so no air goes through the A/C evaporator.

think it needs more coolant added when engine is cold

could be waterpump?
i was going to say rad fan,but if so heater would be hot.
lack of coolant will make heater core to blow cold,if engine heats up with full coolant,usually means poor or no circulation.
water pump?
run engine with full coolant,at operating temp.with rad cap off and look in rad cap hole and see if there is movement of water inside rad.
[rad fan will not come on if water is not circulating through rad water pump?]

Sounds like multiple problem's. The a/c sound's like low on freon.The air bag and ses light are seperate systems from the a/c.Any time the service engine light is on it has to do with the engine system,the air bag is also seperate.Need to take in and have the code's checked for the service light and they can also check the air bag system and see what codes are stored and go from there.

Check the coolant level, it could be as easy a fix as adding coolant because it's low. Low level causes engine to overheat, and low level won't circulate to heater core, so no heat situation even though engine is running hot. Let me know if this fixes it, if not I'll help .