Hi there!
I had the same problem on a 95 Vauxhall Cavalier, it blew cold air out when I wanted hot air and then when the engine warmed up I got steam coming out!! It turned out to be a hole in the Heater Matrix, (an air/water heat exchanger similar to the main radiator at the front of your car, passing cold air over hot water to heat up the air). I bought a bottle of Radweld from my local car accessory shop for about 3 pounds, poured it straight into my coolant system, ran the car for a while and it worked!!
If the problem u've got is the same as mine was, you might have a wet floor in the passenger side footwell. The Heater Matrix is behind the dashboard, in between the drivers and passengers footwell, so if it's leaking, that's where you'll find the water!!
If thats not the problem then maybe a control rod that opens and closes the hot vent has came loose. You did say there was some resistance didn't u?
Glen, December 2005
