I covered this before on another site but here we go again. These are my words, I wrote them and now I'm using them again.
Okay. So two of the three coils were burned out On my resistor pack and my front heater fan ran on fast and fastest only. I thought about getting out my nickel wire and trial and erroring my own coils but I found it much easier to go to the wrecker and buy the 'sealed in ceramic' resistor pack from a previa (the connector was the same though the thing itself is bigger and has a two screw rectangular plate -- look for the fan under the front hood of the newer vans and find the wire and plug to guide you to the pack). Undo two screws. Pay for it. Walk to your Vanwagon and just plug it in. At first mine was wedged half way in to the hole that fit the old one but later I carved the hole bigger and got the whole ceramic block inside the plenum and in to the air stream so the flowing air could do its job in terms of helping cool the part. The fan now seems to have low, medium, medium again and really fast. I can live with this. It was an easy fix.
In any case, the older previa van resistor packs are REALLY easy to find at the wreckers whereas our packs are all pretty much long gone. Just remember: the ceramic enclosed previa pack will get HOT just like our open air coils. (Lower speed setting = more heat). This seems to be fine but if the ceramic is not inserted into an enlargened opening but merely left resting on the plastic plenum it WILL melt the plastic. Once the access hole is carefully made bigger it is possible to set the pack in the air stream and all seems well.