On 26 Dec 2004 13:33:09 -0800, (Winterpegger)
wrote:

Hello,

I live in a newly built house which has a forced-air natural gas
heating system. Aside from the digital thermostat, there is also a
humidistat mounted on the wall. I've been told that the humidistat
controls a fan which exchanges humid indoor air for dryer outdoor air.
I've also installed a central air conditioner over the summer (install
done by an HVAC contractor). Given that it is winter, I'm noticing
that with the humidistat turned on to control the humidity in the
house, the air conditioner fan also turns on whenever the humidistat
kicks in.

Is it just the fan operating, or is the air conditioner unit actually
operating and lowering the indoor temperature?

I've also noticed that the refrigerant line that runs from the A/C
unit into the furnance duct/coils get all covered with a layer of
frost.

Is this normal, or is it a wiring error of some sort by the HVAC
contractor?

The humidistat should control a Humidifier. Nothing else.
I cant see the air conditioning compressor working from here when the
outdoor fan runs. Only you can tell us that.
The A/C compressor nor the A/C outdoor fan should NOT be running in
the winter NOR when the humidistat is turned up.
Youve got some messed up wiring and obviously no one has checked out
your system in your newly built house.
You'd do yourself a favor by getting them or a Good hvac company back
out and have them check everything over including settings, air flows,
temps etc. etc.
Bubba