I just bought a '91 toyota pickup and I've discovered that the heater doesn't work. The guy I bought it from told me that there's a problem with theblower...he said it needed a new heater fan resister, I think? The blower works, but only on high, otherwise it stays off. Besides that, it only blows cold air. I've located the heater core and I'm certain that I can change it myself if that's what's needed, but I think that it may just be the thermostat....So basically there's two problems: 1) The blower isn't functioning properly. What do I need to fix it? 2) No hot air comes out when the heater is turned on. Thermostat problem or heater core, and how can I tell which one it is?