No heat The car blows cold air even when its set at 90 degrees. I know my radiator is full of coolant but there is also another resevoir on the set of the engine for coolant, why is that there?

I doubt it's a heater core.
first look in the radiator and make sure your coolant is full.
not just in the overflow bottle. a bad radiator cap may not allow coolant to refill the radiator . so the radiator can be low and you still have a full overflow bottle

so refill everything and drive it a few miles and see if your heat comes back.

Check the thermostat and the water pump.

push the A/C button to shut it off.

Yes it is.........simply because heater cores are such a pain in the **** to change. Sounds like a good deal.....maybe try to jew them down $100 to cover labor cost! You never know! Good luck!

There could be 3 possible problems here.

If the dashboard is saying the engine is overheating at 90 degrees and there is still cold air coming through then the thermostat could be faulty. I would suggest that you remove the thermostat and place it in a beaker of boiling water. If the top begins to open as the temperature rises, then it is fine. If not, then the thermostat will need to be replaced.

If the thermostat is fine, I would then suggest that you check your coolant levels, the coolant pressure or make sure there isn't a crack in the radiator. If there isn't enough coolant in the system then it won't perform to its highest standards. If the coolant pressure is too low, then it won't be able to cool high temperatures, although 90 degrees isn't very high for the engine to overheat. If your radiator has a crack in it then it will be leaking coolant which would explain a low coolant level and loss of pressure.

A third problem could be air getting into the heating system which will cause air to get trapped in the radiator. This would stop the normal flow of coolant. So now I would suggest checking the cylinder head gasket and do a pressure test to see if there is any air getting into the system.

take the radiator cap off when the engine is cold check the fluid in the radiator,if necessary add fluid to the radiator not the resevoir with the motor running and with the heater on until full leave the cap off untill the motor gets up to full heat and the thermostat is open and pulls the fluid into any unfilled cavities. Add fluid as necessary.

It sure sounds like a stuck-open thermostat to me. The coolant is flowing through the radiator when it is not supposed to. The car does not have any airflow through the radiator when it is sitting still, and when you take off the air blows through the radiator, thus causing the engine to cool down. The thermostat controls the flow of coolant through the radiator to keep the engine at operating temperature.

You have air in the coolant system, check the resevoir and radiator if you can. iy needs to be puged . remove the resevoir cap start the vehicle and let it warm up to operating tempeture. kepp check on the resevoir and fill as needed. if some comes out this is OK, it is purging the air

It sounds to me like you're low on coolant. When you checked the coolant level, did you actually open the radiator cap and make sure the radiator is full? The plastic tank you generally add coolant too is actually an 'overflow' or 'reserve' tank. There is a hose that runs from that tank to the top of the radiator so if the radiator gets low on coolant, more coolant -should- run in from the overflow tank. However in practice this does not always work. I have a Jeep that leaks coolant and experiences this exact same problem. Coolant will not run from the reserve tank into the radiator because the hose is plugged up, and whenever the radiator gets low on coolant the temp gauge will go real high and then drop, and the heater doesn't work well. This is because the cooling system of your car is supposed to be a closed system, full of coolant and no air. When coolant leaks out, the space it used to occupy is now occupied by air, which does not transfer heat well. When 'air' is passing through your cooling system, no heat can be transferred from your engine to the heater and radiator, resulting in a hot engine and no heat at the heater. Then when a pocket of water passes through the system, the temperature gauge quickly falls as the water absorbs the heat from the engine. The hot water that cools the engine is where the heater gets it's heat from as well, so when water passes through the heater core, the heater works, but when it's filled with air, it doesn't.

Replace the thermostat
check and or have the water pump check
open radiator cap start cold engine add coolant
step on gas a bit about 2000rpm add more coolant hold the peddle close radiator cap