I get only cool air from all heater outlets

With the engine at full operating temp, locate the 2 heater hoses where they go into the firewall and feel them to see if they are both hot to the touch. If not too hot to hold, then you have to look at the actual engine temp and if that is up, if it is, then your looking at a restricted heater core.
If you find that they are both too hot to hold, then the heat in that vehicle is controlled by a blend door that regulates heated air flow. It is operated by an electric motor/actuator. The problem can be that the actuator is stripped or inoperative or the door itself could be damaged. This is what needs to be determined by examining the actuator and see if it is responding to heat change commands or not.
If they are both not too hot to hold on to, then you either have a restricted heater core or the system is not completely full and getting air pockets for some reason.

Last Month I had a Jetta in the shop that had "good flow" through the heater core... but no heat.

After pulling the dash I took the old heater core apart:

http://www.youtube.com/watch?v=kQhV49nExaw

Aside from the good advice by Wrenchtech.... if you have ever found foam coming out of the vents... the heater flaps aren't sealing and need to be repaired.

Thomas