[Hai-users] resetting tstat

[Joseph K. Vossen]

I don't rcall if I have a common or not; I'll check this out.

My furnace works a bit different than what you described; I don't see the fan 
turn on during the beginning of the cycle.  What happens in my case is that 
the burners kick on for about (I guess) 30 seconds (I assume to warm the air 
in the furnace so the system does not blow cold air through the house) and 
*then* the fan kicks on.  I do notice what you described when the tstats call 
for cool; fan first runs for about 15 seconds, stops, compressor kicks in and 
then the fan starts up again.

I don't know if this makes a difference, but I have a zoned system; 3 HVAC 
units, each with 3 zones for a total of 9 tstats.  I usually see this problem 
on one tstat, *sometimes* on one other one.  It mostly ocurrs when using 
heat, but I have noticed it once or twice with the AC.  These tstats are 
about 8 years old.

thanks

On Friday 18 November 2005 09:49 am, Brett Griffin wrote:
> I usually notice this during initial testing of a installed thermostat with
> Gas Heat.
>
> Do you have a common running between the thermostat and the Furnace?  This
> usually fixes this issue.
>
> The problem I see this with is as follows.  The Rc-80 calls for heat.  The
> furnace fan turns on to evacuate any possible gas in the burn area.  This
> last for about 30 seconds.  At the end of this 30 second evacuation period
> is when the problem happens.  Gas furnaces start an ignition cycle to
> create heat.  The furnace uses too much of the available power to the
> thermostat for this process, and the RC-80 sees this as a power failure,
> and "resets". This usually makes the thermostats turn off and then back on,
> but then disable the thermostat from operating the furnace for safety
> reasons.
>
> By adding the common wire, this usually allows enough current for the RC-80
> to operate.  If not, a second option would be to add a 24vac power supply
> in parallel to the red and common terminal of the thermostat.  However if
> you use the second power supply option disconnect the common from the
> thermostat to the furnace.  A even better route for this is the Thermostat
> isolation board made by HAI.  It powers and isolates the thermostat
> electrically from the furnace.
>
>  Brett Griffin, Home Technology Consultant
> Architechtronics, Inc.
> www.architechtronics.com
> www.hometechdiy.com
>
> -----Original Message-----
> From: hai-users-bounces at tssi.com [mailto:hai-users-bounces at tssi.com] On
> Behalf Of Joseph K. Vossen
> Sent: Friday, November 18, 2005 4:57 AM
> To: hai-users at tssi.com
> Subject: [Hai-users] resetting tstat
>
> Sometimes (maybe once or twice a year) some of my RC-80 tstats refuse to
> 'call' for heat or cool despite the fact that the temp in the room is
> above/below the setpoint.  The only way to get it to 'call' is to remove
> and
>
> then reapply power to the tstat.
>
> While this is normally not a real problem, I am worried that this may
> happen
>
> when we are out of town for a length of time and the heat does not come on.
>
> Any collective words of wisdom?
>
> thanks
>
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