Heat Less in the Carolinas

Phil Rose pjrose at frontiernet.net
Sun Dec 4 14:58:52 EST 2005

Addendum to my earlier post.

Here's an excerpt from an old post of mine--describing the CC channel 
08 and 09 codes in a bit more detail and mentions using CC channel 01 
as an additional diagnostic tool (showing  potentiometer/flap 

>During normal operation an equilibrium
temp eventually is achieved when the inside temp-sensor agrees with
the temperature setting. At that point the heater control flap
arrives at some corresponding "equilibrium" position, and
consequently the (feedback) potentiometer sits at a particular
position on the variable resistor. Over the course of years, a small
range of equilibrium flap positions tends to be used--over and
over--and hence that same range of the potentiometer is rubbed and
worn and becomes unreliable. [Please note that the potentiometer
might also cause similar problems because of "dirty" vs "clean"
sections--i.e., sort of the inverse of the "worn-out" situation.] So,
for some range of flap positions, there will be considerable "noise"
(or drop-outs) in the resistance value fed back to the climate
controller. The CC thinks the position is in error so it causes the
motor to hunt around (in ever-increasing circles) for the right
value--eventually parking it at its extreme-frustration position,
which is lots of cold air. You can observe this happening on CC
channel 08, which displays the  feedback-pot signal. Normally the ch
08 value should closely match the target value (displayed by CC
channel 09). When this isn't the case, the error shows up as a
reading of "07" (instead of "00") on channel 01.  You can get a good
idea of when the flap/potentiometer position reaches an unstable
region (i.e., bad spot on the potentiometer) because the 08 channel
suddenly begins "hunting" wildly and eventually settles in at "255".
Then you know you're gonna get cold.<


Phil Rose
Rochester, NY
mailto:pjrose at frontiernet.net

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