"Glen Cooper" wrote in message
...
Hi gang,

A friend called. The HVAC fan runs all the time in her 1 story home built
in 1979. She has a digital stat above her return duct in the hall, the
only
return, 1700 square feet or so.

The problen started when she used the heater for the first time last
season
a few weeks ago, Houston, Texas is hot most of the time. :-)

I have no specifics: model, make, electric or gas, original unit...

She has a digital stat. It is set to Auto..

I am not a pro HVAC man, I am a locksmith, I make lost car keys. That
said:

I think the possible cause IS NOT the thermostat (she wants to buy this
first), but a relay AND/OR a thermal limit switch located by the heater
output on a PCB or on the side of the attic unit some place, (max limit
switch with a double pole [winter/summer push/pull switch depending on the
year of production and ajustable temp settings?). I think the heater
switch is effecting the AC too because the heater around here isn't used
much and once it shorts it shorts and you know.., (now she says the AC fan
stays on too), it shorted last year. (Would this be correct?).

She can cut the AC or heat off or on at the stat, the fan stays on hi BTW,
not low which I understand happens up north on purpose to allow the
basement
air to go upstairs and vise/versa to lower the bill, not that complicated
here. We don't have basements being Houston.

That said, Possible causes;

(1) Bad limit switch?
(2) Bad fuse or relay on PCB controlling limit switch?
(3) Bad relay from thromastat controling fan? (Note: style of heater
unknown)
(4)Rat bit the stat wires shorting the green control wire to the feed
wire?
Naww...)

Am I missing something, Thanks. Tomorrow is Sunday. Thought I could help
her out while not doing nothing else.

Ed

We could guess for hours, the only real way of correcting the problem is to
go there check the settings. I remember when I moved into my last house with
a digital stat, took me a couple of weeks with the manual to get it working
the way I wanted.

Any of the above are POSSIBLE, I would WAG doubtful. Go on line get the
manual for the stat, then set all of the variables for her. or call someone
on Monday. Personally I would never attempt working with locks.