By switch the passenger side up he means close the vents so it's all concentrated on the driver's side.. At leat that's my guess.
The HEVAC blower on the Workhorse with Evans HEVAC does indeed use a standard Chevy blower.. I have two of them, one is salvage from a pick up truck.
The system kind of works like this
You have a switch that sends power to one of two leads on a resistor, the resistor is in "Front" (under the hood) in front of the passenger seat in teh air plenum. This feeds the motor
FOR low and medium speeds the switch also feeds a "low speed relay" which actually passes the power to the resistor.
For HIGH it feeds the HIGH SPEED RELAY which feeds, I believe, the top terminal on the resistor (Which is also the one the blower connects to)
If you are not getting high speed there are three possible situtations.
1: High speed relay failed so you only get low speed.
2: Wrong blower, not the motor, but the blower.
3: Bad connection somewhere along the way.. Blower motor ground is suspect number one
TO TEST blower motor ground
Run blower 5 minutes and using a dampened finger feel the screw. if it's hot (tap it may be very hot and if you tap with a dampened finger you do not get burned, think frying pan hot or steam iron hot) then remove screw, clean paint off with Wire Brush on Dremel and replace screw and lug.
Home is where I park it!