Air blows cold, then warm every few minutes...sometimes cools for weeks

SOURCE: 2001 Hyundai Sonata V6 engine fails to warm-up - fans don't work

The sensor is located at the radiator. follow the wire from the fan to the plug on the sensor. I hope this helps.

SOURCE: Heater blower problem

under the hood of the car on the passenger side you will see a round motor sticking up.thats the blower motor there should be 3 screws holding it in place and one plug to unplug.you lift the old motor out and put the new one in in its place

SOURCE: from cold start engine warms to quater temp then

Does the Check Engine light come ON when this happens? Whenever the "Check Engine" light comes on, there is always a DTC (Diagnostic Trouble Code) stored in the ECM (Engine Control Module). You'll need an OBDII (On-Board-Diagnostics) scanner to retrieve any codes recorded/set in ECM. Otherwise, guesswork. I have MANY ideas that could send you on a wild goose chase. I strongly suspect EMS (Engine Management System) sensor beginning to malfunction as it warms up. First strong suspicion is the crank position sensor (CKP) - however,usually always sets a DTC (i.e., P0335, P0336). The next suspicion is the Engine Coolant Temperature sensor. The ECM uses this sensor's signal to adjust fuel, timing, engine RPM, etc based on engine temp. If malfunctioning at a particuar point during engine warm up, it could be telling the ECM the temperature is LOWER or HIGHER than it ACTUALLY is, resulting in the ECM to increase fuel (flood it) or give it LESS fuel (starve it). If this malfunction lasts long enough, the ECM will usually set a DTC for that sensor circuit, either a Range/Performance code, or a "LOW Input" or "HIGH Input" code.

SOURCE: AC will blow cold air for a few minutes then start

you have moisture in the system this causes your expancion valve to freeze up an stop working, thats why it works for sort time and when it de-freezes stars working again. you need to do a EVAC & RECHARGE with a good AC service equipment, specially attention to pull vacumm por at least 20minutes so you get all moisture out of the system.
Good luck

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SOURCE: no heat 06 sonata only blows cool air

it most definitely is your blend door. It's a bit of a hassle but in the end it doesn't cost anything but a sore back/neck and hands. Take your time. remove glove compartment, and you'll see the blend actuator. I unplugged mine as it was stuck in 'cold' mode. after re-plugging it worked again and has been fine since.