PREVIA 1992 NO HEAT

If your Previa's low/medium speeds on the blower (ac/heat fan) have stopped working, but the high speed works, you most likely have a problem with your blower motor resistor. Here's how to access the resistor. These directions may be slightly incorrect since I finished this procedure about an hour ago and I'm typing this from memory. But they should get the job done. It took me about 30-40 minutes to do this from start to finish:

Remove cabin air intake duct (two philips screws)
Remove one bolt holding antifreeze reservoir in place, move reservoir aside.
Remove two bolts holding brake fluid reservoir in place, move reservoir aside.
Unsnap recirculate/fresh selector cable from blower housing (on vehicle-left side of housing)
Remove angled metal arm from vehicle-right side of blower housing (attaches to firewall with nut and to housing with bolt).
Remove two bolts (at vehicle-front of housing) that hold the upper and lower blower housings together.
Remove nuts on firewall holding upper blower housing in place, and begin to work upper housing out of vehicle, disconnecting the 4 electrical connectors as needed (2 connectors are on top and 2 are down beneath the blower housing).
Remove nuts on firewall holding lower blower housing in place, and remove lower blower housing from vehicle

Look on the lower blower housing, on the side which was facing the firewall, and you'll see a white ceramic block (approx 2-3 inches long). This is the blower motor resistor. There are 2 contacts on the resistor that should be joined by a springy curved band. If the band isn't bridging the two contacts, it's likely that the soldier has melted/broken, and this is what's causing the low/med speeds to not work. Solder the band back in place and this should correct the problem (it did for me).

If you have 150k on it, you may need all three. Run the engine, turn on heater, and get out and slam the hood a couple of times. In extreme cold or hot weather, this may get you by for a few days. I went 3 or 4 months with a bad blower by doing this, when the brushes inside the motor went bad. If it does not work, your blower is probably bad. The switch can have bad contacts, and you may try moving or holding it vertically to see if you can get any activity out of it. Put a resistor in too, if you have to replace the blower motor.