Car: 1989 Mercedes 300SE


So, I bought this car in September. I recharged the AC, and it works great still today.

But, this winter I tried firing up the heater. I rolled the climate control temp to max heat, and I got cool air. It stayed that way, no matter how long I drove. I went 60 miles on the freeway and it still didn't warm up. However, the AC still blows very cold.

After trying to get it to work everyday, it did something.

It warms up a little (definatly not hot) when I am at idle for a few seconds, and then immediatly cools down when I take off.

If I run the fan at th lowest speed, it will come out very slightly warm. If I turn up the fan, it immediatly goes cold.

So what's up? Anybody have this problem before? Is it a temperature sensor, or maybe a leak? Any ideas or thoughts would be appreciated.