Why do I not have heat but I have air conditioning?

What is your question?

My truck currently does not have heat, but the air conditioner works just fine. My thermostat will rise in the summer time with the air conditioner running, but when it is switched to hot air, the thermostat does not rise at all. I occasionally hear a clicking coming from my glove box area, but it is not a constant. My coolant levels seem to be just fine. Help!