Ford Repair: heater, head gaskets, temperature gauge

Question
I have a 1994 Explorer XLT.  The heater started blowing cold air last night and at one point, while driving home, the temperature gauge went into the 'Red'.  When I turned off the heat the temperature gauge went down.

Is it some kind of heater core valve?  What is the repair job like and how much should it cost?

Thank you,
Steven

Answer
Hello and thanks for the question...I'll try to help.
 First, check you antifreeze level. If it's dropped, you might want to find out where the leak is. The radiator should be full, as well as the resivoir. If it isn't, I would start looking for the leak. The common places are hoses, radiator, heater core, head gaskets.
Hope this helps,
Erik