Climate control, '89 100Q, temp sensing

[FMARTIN <fmartin@ithaca.edu>]

Hi folks.

I'm still puzzling over why my CC runs hot nearly all the time. The cable 
(Bowdin?) seems to be putting the flaps through all their proper motions, as 
far as I can tell, with my head (way) under the dash.  The valve controlling 
the flow of engine coolant seems to be working (shuts all the way when I put 
system at "low"). I do *sometimes* get the flashing red light at the temp. 
indicator. (I think this may be saying that the freon pressure is low (?).)  
The system seems to work, briefly, if I run it through the extremes of its 
ranges, then bam, full hot.     Questions:

1) a recent post by Steve Buchholz (thanks!) to someone confirmed my guess 
that that little grating on top/center of the dash deals with interior-temp. 
sensing. My suspicion has been that whatever the device is, it's not working, 
so the system defaults to full-heat.  How do I check that spec. item, and 
importantly, how do I get to/remove it??  Some idiot (ok, me, last nite at 
10:00), while carefully (!) trying to pry at it, broke one of the small fins, 
which of course fell down to Neverland.  My wife reports a strange/annoying 
buzzing from the dash this morning, and is not impressed.

2) does that valve that controls coolant-flow to the heater core either sit at 
full open or full closed?  Since it's vacumn actuated, I can't imagine it has 
an intermediate point.  True?

Thanks much for any help.

Frank M. 
'89 100Q
'88 Mazda 323 GTX