I replaced the heater core in my 95 Mustang, what a fun time that was. But there is a problem. Now when I have the temperature setting at cold and the climate knob at vent, some warm air comes blowing out, even if i switch to max ac I get the same temperature. (If anybody wants to experience what hell is like, I'd be more than happy to give you a test ride, she takes about 2 minutes to warm up!)

So I checked my freon levels, everything is good and to the right pressure. The only oddball thing is that for some reason is that I topped off the Radiator fluid when I put the core in and it was an inch below the marker for full cold on the degas bottle (antifreeze tank). So i put some stuff in it and it was cold for a while. Now today its hot again and its low on coolant. There are no drips underneath the car, and there is no antifreeze on the dipstick and no oil in the tank. Can somebody help me? Its driving me nuts!

for the problem of not switching from hot to cold u may have unplugged and forgot to replug in a vacuum line on the hvac system under the dash. and for the coolant problem, does your car have a white smoke upon start up, if so it has a leaky head gasket that is leaking coolant into the cylinders, ect. good luck.