When I purchased this truck from my Uncle, Saturday, he said that the 'flap that controls the outside air from coming in is not working'

This is why the air is only lukewarm....

Well, I got my service manual CD in the mail today and fired it up, revealing this diagram:




ANYWAY, I inspected my setup, and it all looks like its in tact. i moved the diagragm back and forth, to see if I could determine what's up with the blend door, and I could hear it opening/shutting inside there.

So IF this really is the problem, it's not the door, but the diaphragm.

How do I test it out for sure???

I have a Mityvac vacuum tool, i was curious if I could hook it to the diaphragm to check and see if it works or not.

When does the diaphragm have vacuum applied?

- - -

On a side note, what else should I check out (as the blend door might not be the problem)

I was gonna try and get at the heater core, to put my hand on it and see what the temperature is like.

I notice the temp guage on the truck hovers between C and Normal.

Is this correct, or should it be dead center on NORMAL??

I bought a new thermostat Sunday, and am going to install it once it warms up a bit.

Any other ideas?

The coolant level (according to the reservoir) seems to be correct.

Thanks,

Luke