On Thu, 2011-07-21 at 13:08 -0700, jim@jpes.com wrote:
> Herbert,
>=20
>  Just a thought I had while reading this.  If for some reason when the
> compressor turns off at the end of
>  one cycle, and then the thermostat calls for more cooling and the
> pressure hasn't beld down on the
>  compressor, you may have a condition where the compressor is trying to
> start while there is still a
>  pressure head on the high side of the line.  If this is the case, the
> compressor either won't start at all,
>  or will struggle to start, and wind up trippin the overheat sensor and
> cutting power to the compressor.  If
>  that happens, you'll have to wait for the heat to subside before the
> thermal switch can reset.  This might
>  take anywhere from a few minutes (warm outside - 75F) to maybe an hour
> or moe (hot - 90F+)
> =20
>  I don't know if this is what's happening, but the symptoms sort of
> support the theory.  Maybe it's
>  something you could watch for in your investigation with all of the
> sensors you have available.

That is exactly the train of thought I've been going on. The thermostat
seems to have a 10 minute guard period, after it turns off it doesn't
ever seem to turn on again until 10 minutes have passed. I'm wondering
if that's long enough.

Something I didn't want to mention since it's so fleeting is every once
in a while, when I see the "long time to start" situation, my power
meter registers 2 to 3x normal power usage for the 1 minute interval
(normal power usage is 1.2kW, I've seen 3 and 5kW reported).

If this is the case, perhaps I can either set the thermostat to have a
longer guard interval, or replace it with one that has a longer one.
Does 10 minutes sound right to people?

The good side of all this is I've learned ALOT about AC systems, enough
that I might experiment a little when I have time.

Thanks, TTYL



--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.