I have a Honeywell thermostat T4039M1004 that I would like to replace
with a high-end digital thermostat.  It is operating on 120v and has
Lo-Med-Hi fan speed selector, manual On/Off, and a heating or cooling
slider.  Any suggestions on alternatives? There are five wires per the
Honeywell schematics for the T4039M

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Request for Question Clarification by redhoss-ga on 10 Oct 2006 13:21 PDT

You probably know this, but what you have is called a "line voltage"
thermostat. There are line voltage digital thermostats available for
heating only and maybe for cooling only. I don't think that there are
any available exactly like you seek. Would you consider two separate
thermostats. I see why you came to this forum.

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Clarification of Question by vorlonblack-ga on 10 Oct 2006 14:50 PDT

Hi Redhoss, it's definately not a typical residential type of a
thermostat.  It's a fan-coil 4 pipe SPDT thermostat.  I've seen a few
thermostats from Honeywell that are digital for fan-coils but I cannot
tell which variant I need.  For example there are 1 and 2 relay
versions, manual vs auto heat/cool etc.

Unfortunately, I can only go with 1 control for safety reasons because
this thermostat controls both the heat and cooling via a single blower
motor for both.  If both thermostats were activated it cause the gas
heater and A/C to kick off on the same system, blowers, duct work,
etc.

You could use relays and a transformer for control voltage. Then you
would have a large choice of low voltage digital thermostats.