Climate control question re: '87 5kTQ

[Wallace Offutt]

Question for you folks:

The previous owner of my '87 TQ for reason had replaced the heatercontrol 
valve with a straight piece of pipe. When I found how cheap the valves are, 
I figured there must be a reason for this... Well, now that it's getting 
could out, I'm beginning to get an idea: the heat seems to always be on when 
the system isn't turned on (but w/out the blower running), but when I turn 
the system on (regardless of whether I choose econ, auto or what, and 
regardless of what temp I select) the AC seems to turn on. I figure it might 
be some module I read a vague description of that lies somewhere behind or 
beneath the glovebox... any thoughts?

Thanks,
Wallace