2
Let’s try our guide out using the EXAMPLE section below, and see how it works. Suppose that the problem is a defective low heat pressure
switch (for example the contacts will not open). This is an internal problem and cannot simply be seen. We go to the START HERE section
to Step 1.
EXAMPLE
Start Here Section
STEP
ACTION
YES
NO
GO TO
1.
Step 1 tells us to remove main furnace door first and NOT TO REMOVE THE BLOWER
ACCESS PANEL. It then asks the question, “Is AMBER LED status light on?”. If the low
heat pressure switch was defective, a pressure switch did not open status code would be
flashing, so the answer is YES. We go to Step 2.
2
19
2.
Step 2 asks the question, “Is the AMBER LED status light blinking rapidly without a
pause?”. If the low heat pressure switch was defective, a pressure switch did not open
status code would be flashing, so the answer is NO. We go to Step 4.
3
4
4.
Step 4 asks the question, “Is the AMBER LED status light blinking ON/OFF slowly with a
combination of short and long flashes?”. If the low heat pressure switch was defective, a
pressure switch did not open status code would be flashing, so the answer is YES. We go
to Step 5.
5
7
5.
Step 5 tells us to determine the status code. The status code is a 2 digit number with the
first digit determined by the number of short flashes and the second digit by the number of
long flashes. So we count the short and long flashes and see that status code 23 is flashing
and go to Step 6.
6
6.
Step 6 tells us to go to status code 23 section
INDEX
GENERAL
The furnace must have a 115--vac power supply properly
connected and grounded. Correct polarity must be maintained to
enable gas heating operation.
The gas service pressure must not exceed 0.5 psig (14--in. W.C.),
and no less than 0.16 psig (4.5--in. W.C.).
Thermostat wire connections to the furnace at R and W/W1 are the
minimum required for gas heating operation.
W2 must be
connected for 2--stage heating thermostats.
Y/Y2 and G are
required to be connected to the furnace for single--stage cooling
and heat pumps. Y1, Y/Y2, and G are required for two--stage
cooling and heat pumps.
G is required for continuous--fan.
C
OM
--24V is required for some clock thermostats.
These
connections must be made at the 24--vac terminal block on the
furnace control. (See Appendix A)
This furnace can be installed with either a single--stage heat/cool or
a two--stage heat/cool thermostat.
UNIT DAMAGE HAZARD
Failure to follow this caution may result in unit damage.
This furnace is equipped with a manual reset switch in the gas
control area. The switch will open and shut off power to the
gas valve, if a flame rollout or overheating condition occurs in
the gas control area. DO NOT bypass the switch. Correct
inadequate combustion-air supply, component failure before
resetting the switch.
CAUTION
!
Before operating the furnace, check each manual reset switch for
continuity. If necessary, press and release the button to reset the
switch.
SEQUENCE OF OPERATION
Using the schematic diagram in Appendix A, follow the sequence
of operation through the different modes. Read and follow the
wiring diagram very carefully.
NOTE
: If a power interruption occurs during a call for heat
(W/W1 or W/W1--and--W2), the control will start a 90--second
blower--only ON period two seconds after power is restored, if the
thermostat is still calling for gas heating. The amber LED light
will flash code 12 during the 90--second period, after which the
LED will be ON continuous, as long as no faults are detected.
After the 90--second period, the furnace will respond to the
thermostat normally.
The blower access panel must be installed for power to be
conducted through the blower door interlock switch ILK to the
furnace control CPU, transformer TRAN, inducer motor IDM,
blower motor BLWM, hot--surface igniter HSI, and gas valve GV.
1. SINGLE--STAGE THERMOSTAT AND TWO--STAGE
HEATING (ADAPTIVE MODE)
NOTE
:
The low--heat only switch SW1-2 selects either the
low-heat only operation mode when ON, (see item 2. below) or the
adaptive heating mode when OFF in response to a call for heat.
(See Fig. 1.) When the W2 thermostat terminal is energized it will
always cause high-heat operation when the R to W circuit is closed,
regardless of the setting of the low-heat only switch.
This furnace can operate as a two--stage furnace with a single--stage
thermostat because the furnace control CPU includes a
programmed adaptive sequence of controlled operation, which
selects low--heat or high--heat operation. This selection is based
upon the stored history of the length of previous gas--heating
periods of the single--stage thermostat.
The furnace will start up in either low-- or high--heat. If the furnace
starts up in low--heat, the control CPU determines the low--heat
on--time (from 0 to 16 minutes) which is permitted before
switching to high--heat.
If the power is interrupted, the stored history is erased and the
control CPU will select low--heat for up to 16 minutes and then
switch to high--heat, as long as the thermostat continues to call for
heat. Subsequent selection is based on stored history of the
thermostat cycle times.
The wall thermostat ”calls for heat”, closing the R to W circuit.
The furnace control performs a self--check, verifies the low--heat
and high--heat pressure switch contacts LPS and HPS are open.
a. Inducer Prepurge Period -- The furnace control CPU
turns on inducer motor IDM and slowly increases the
inducer motor speed. When the low--heat pressure
switch LPS closes, inducer motor RPM is noted by the
furnace control CPU, and a 25--second prepurge period
begins. The RPM is used to evaluate vent system