No Heat :(

My 92 Jetta Diesel does not blow hot air, this is important, I live in Canada.

I have recently had a whole slew of repairs done, including replacing the engine entirely. I replaced the heater return hose myself.

Anyone have any Ideas what the problem may be?

The heater box has flaps that direct air flow. They are made of metal with large holes to make them light and covered with foam rubber to make them relatively air tight. The foam deteriorates and the vent air from outside blows in. To fix this you have to remove the heater box which involves removing the instrument panel and dashboard. It's an all day job. I've never tried to do so, but taping plastic over the fresh air intake vent (under hood, passenger side, close to windshield) may do the trick. If it works, let me know.