Heater Heater blows warm then cool on S40 T5 Six speed
 

Need a little help again!:o 2005 S40 T5 bought new in Sweden with a 6 speed manual...love this car...blows cool air instead of heat.
Start up car and heater will blow warm then fades out to cool. No overheating with engine, everything else fine. Dealership said they couldn't diagnose in hot summer weather. Sooo...looking to try to fix it myself. Any and all help appreciated:) as weather is turning to fall/winter.