I have done a lot of work to the hvac system on my 1994 6.0 v12. I have replaced the compressor, had it re charged and a
So had the heating fixed. However whilst it is cold when required and hot for defrost, it does not seem to regulate to a temperature it blows cold most of the time. Somebody suggested checking the climate sensor in the passenger side, I looked at it and the fan is still running ( does that mean it is working?). Anybody else had this issue?

 

it may be a blend flap problem. I think the hot and cold is present most of the time and the system just mixes the two to achieve the set temp.
I am not familiar with the very late setup but have been able to get stuck blend flaps operating in the '89 system simply by some gentle tapping on the blend flap servos.

 

Here are a couple of documents that may help

The defrost and centre vent temps are controlled by the blend flaps, in the upgraded system in your car the temp should be the same for defrost and normal operation if the temp is left the same.

Your system is a little different than the word doc but it should give you enough to at least help with diagnostics.