1994 Ford Crown Victoria Overheating problems.

Heater problem
1994 Ford Crown Victoria V8 Wheel Drive Type unknown Automatic 150000 miles

OK. So it's my husband's car and he won't ask anyone for help even though he doesn't know what he's doing so I will.
It's had several problems lately. Started with the remote start going out. Then the car quit running all together. It turned over fine to accessories, but would go no further.
Got it jumped and it started only to quit when he got home and wouldn't even start with a jump.
Replaced battery cables and connector and car started fine.
Now we are back to square one again with more problems than before.
Car died, started with a jump. By the way, battery had been tested and is at 100%.
Now it is having problems with that AND overheatiing. The needle jumps way up when it is driven any distance at all. Coolant has been filled up and all that looks fine. He has also tested the thermometer using the boiling water method.
The heater its-self is not blowing out hot air at all. So that's not a possible way to release built up hot air.
Any ideas on where to go from here that would possibly keep us out of a mechanics shop?
We have read several different places to check the radiator cap. But he's not sure what he's looking for and I don't think that would make the heater stop to. But then, I don't know a low about cars. Any ideas would be greatly appreciated!