The max blower speed actually bypasses the resistor. It goes through a relay. However, the relay and resistors are one unit
Here’s what the resistors and relay look like
Do you have sufficient coolant level?
Look in the reservoir, and also look in the radiator itself. Do this with a cold engine!
Is the engine getting up to operating temperature?
Start the engine, drive the van for a few miles. Keep it idling and pop the hood. Feel both heater hoses. Are they both hot?
Is the airflow coming out where you want it to, or is it only coming out the defroster vents, at the base of the windshield?
How many miles?
Any significant rust?
Do you feel the van was maintained reasonably well?
Does the transmission shift well?
No check engine light on, I hope?
To be sure, this van is kind of old, but the 4.3 liter V6 can last a long time, if you don’t totally abuse it
Not sure about the radiator questions. Coolant level is perfect and it looks good - no rust or discoloration noted in the fluid.
Rebuilt transmission that has some up shift issues when you are at higher speeds and need more power quickly. It did a delayed down shift today but no hard jerking.
No, the air flow is not coming out where I want it to. It kind of seeps out everywhere even when you can hear the variation in each of the blower speeds.
No check engine light on.
Rust is non-existent. It has stayed in New Mexico all its life in the desert areas.
So should I replace the blower motor as a starting point? That is only $40 and I think I can do it myself.
If, as you say, you can hear the variation in each of the blower speeds, it can’t be the blower motor. If it seeps out everywhere then the doors in the ducts aren’t opening properly.
But the last level of the blower (full blast) doesn’t work at all.
As @db4690 said the highest speed is controlled by the relay on the resistor module. Either this relay has failed or the speed switch is not making contact for the highest speed. You also can’t rule out a wiring or connector problem.
GM is well known for burnt electrical pigtails . . . including on the Safari
Those sound easy enough. Thanks for the advice folks. I think I am going to just give the van back to its owner and look for something else once we get moved.