Blower or Switch? and another AC question or two

[mdwilf]

I'm wondering if someone's experience can save a some time standing on my head with a voltmeter - my blower works on the two lower speeds, but not high - I assume this means I have a switch problem because it just sends different 'signals' to the fan for each speed?

Also, my truck is pretty much original w AC - on the pass fenderwell there is a little valve that appears it may have been a vacuum operated affair to shut off the water flowing to the heater core - is this original & are those of you with AC setups running this, or do you just rely on the doors in the heater box to stop the heat?

Thanks