92
FIGURE 52
24-VOLT TERMINALS
NON-COMMUNICATING
THERMOSTATS
THERMOSTAT WIRING
NOTE: For fully modulating function
with a non-communicating thermostat,
the furnace must be installed with the
(-)HC-TST412MDMS Modulating
Touch-Screen Thermostat.
NOTE: Do not use 24 volt control wire
smaller than No. 18 AWG.
Wire all non-communicating ther-
mostats to the 24V connections on the
integrated furnace control. See Figures
53 through 58.
NOTE: A larger wire gage may be be
required for longer lengths of thermo-
stat wire.
For proper installation of the Variable
Output Thermostat, follow the
“Thermostat Installation, Programming
and Troubleshooting Manual” included
as section II of this manual. For proper
installation of a Single-Stage or Two-
Stage Thermostat, see the Installation
Instructions included with the thermo-
stat.
➤
FURNACE OPERATION USING
MODULATING, SINGLE-STAGE, AND
TWO-STAGE THERMOSTATS
The modulating furnace is also capa-
ble of operating with a traditional sin-
gle-stage or a two-stage non-communi-
cating thermostat as well as the modu-
lating (both communicating and non-
communicating) thermostat. The con-
trol will operate with either single-stage
or two-stage non-communicating ther-
mostats as a modulating system using
an algorithm that utilizes three distinct
firing rates; 40%, 65% and 100% of
the furnace heating capacity (See
below for operation of each).
Figures 53 through 58 detail how to
wire the modulating furnace for opera-
tion with non-communicating modulat-
ing thermostat, single-stage thermo-
stat, or two-stage thermostat.
➤
FURNACE OPERATION WITH A
MODULATING THERMOSTAT
As described previously in this manual,
operation with a non-communicating
modulating or communicating thermo-
stat when installed as shown in
Figures 54 and 55 are fully modulating
between 40% and 100% of furnace
capacity. The firing rate is first deter-
mined by the thermostat and then sent
to the furnace. This is the optimum
mode of operation and will give the
best temperature control with minimal
temperature variation from the desired
set point.
WHEN A NON-COMMUNICATING
(24V) MODULATING THERMOSTAT IS
INSTALLED, DO NOT APPLY 24VAC
TO V/W2 AT THE FURNACE CON-
TROL (THIS IS SOMETIMES DONE
DURING SETUP, TROUBLESHOOT-
ING AND/OR WHILE DIAGNOSING
PROBLEMS). DOING SO WILL DAM-
AGE THE THERMOSTAT.
➤
FURNACE OPERATION WITH A
SINGLE STAGE NON-COMMUNICAT-
ING THERMOSTAT
To operate the furnace with a single-
stage non-communicating thermostat,
set switches 2 & 3 of S4 (See Figure
41) to the “OFF” position. Note that
these switches should be in the “OFF”
position from the factory. The lack of the
modulating “V” signal will automatically
be sensed as a single-stage thermostat
and the furnace will operate according-
ly.
THERMOSTATS
With a single-stage non-communicat-
ing thermostat (installed as shown in
Figure 56), during a call for heat, the
furnace will operate as follows:
Phase 1: 0 to 5 minutes = 40% of
furnace capacity
Phase 2: 5 to 12 minutes = 65% of
furnace capacity
Phase 3: After 12 minutes = 100 %
of furnace capacity
N
NO
OT
TE
E:: If the call for heat ends dur-
ing any phase, the furnace will termi-
nate immediately at the firing rate of
that phase.
If switches 2 & 3 of S4 are in the
“ON” position, the furnace will
always operate at 40% with a single-
stage non-communicating thermostat
installed as shown in Figure 57.
THIS CONFIGURATION IS NEI-
THER RECOMMENDED NOR
APPROVED.
!
WARNING
