I have a 2004 Sante Fe 4 cyl. The check engine light came on and the codes were:P0300, PO446 AND PO 320. I had the IGNITION sensor replaced. the check engine light is still on and now I'm getting the following codes: PO300, PO300P, PO301, PO301P, PO302, PO302P,PO303, PO303P , PO304, PO304P, PO320, PO446, PO446P. In addition, the HVAC stopped blowing and had the control assembly replaced. It worked for 3 days and quit. I can feel cool air coming out, but barely. Does anybody have any ideas?

OK To start with, you need to forget about the air conditioner until you get your engine running correctly. The HVAC is controlled by the Powertrain Control Module (PCM). The PCM is probably not allowing the HVAC to run due to all the engine misfire codes you are getting. It may be someting else, but until you get your engine running right, you could be spinning your wheels.

I have no clue what you are talking about when you say "Ignition Sensor" - there is no such sensor on any vehicle that I am aware of. There are many sensors that can affect the ignition like the Crankshaft Position Sensor, but none are called "Ignition Sensor".

P0300 Simply means that there is more than one cylinder misfiring.
P0301 means that cylinder #1 is misfiring, P0302 means that cylinder #2 is misfiring, P0303 means that cylinder #3 is misfiring, and P0304 means that cylinder # 4 is misfiring. (these are what are known as "current faults". The codes ending in "P" mean the same thing, but they are "pending" codes. Current faults MUST be dealt with FIRST.

The P0446 is not a valid code for a 2003-2005 Hyundai Santa Fe as far as I can tell. I tried to look the code up by application and it simply is not there. You may want to read the code again. Sometimes, if you are reading the codes with a "generic" OBD code reader, it will give the closest description it can for a "Vehicle-Specific" code. They are not allways correct. You may want to scan your computer with a scanner that is equipped with the Vehicle-Specific software for your vehicle. You will probably get a different rendering of the code.

The "generic" description of P0446 is "Evaporative Emmission Control System Vent Control Circuit" Again, the DTC list for your vehicle lists similar codes: P0445, P0447 and P0448, however it skips over the P0446 code. If you in fact have a problem with your EVAP vent solenoid circuit, it could, concievably be the cause of your misfire problem. It is possible that the vent solenoid is causing a huge vacuum leak. NOT LIKELY that it is causing the misfire codes, but POSSIBLE.

Anyway, there are literally HUNDREDS of parts that can be the cause of a misfire. This needs to be PROPERLY DIAGNOSED to determine the cause. It could be anything from worn-out spark plugs, a vacuum leak, a faulty fuel pump, all the way to a blown head gasket or cracked cylinder head. Whatever the actual cause may be, it is obviously affecting all 4 cylinders. (This will rule out some things).

Please also review this article:
What Else Could Be Wrong?