Resistor Block question

I've seen the posts for the resister block problems. I have the same problem with one difference; I only have one speed left, but only enough heat to keep the windows clear. Once for some reason they started working again and I had lots of heat, but then it went back to one speed (high) and very little heat. Doea the resistor block control the heat at all or am I looking at changing the thermostat too?

I would fix the Resistor Block problem first (you KNOW that's broken). The Resistor Block controls the speed of the Blower Motor. Lack of heat could be thermostat, heater core, water pump, variable air temperature control slide switch or the underdash door(s) that control the mixture of hot and cold air.