47
H Fitting
Restricting Orifice
Restricting Orifice
The H-fitting
“conditions”
the negative
pressure
signal which
is applied to
the gas valve
"H" Fitting
The low pressure switch assembly includes an H fitting as-
sembly and tubing that provides pressure signals to the
Honeywell amplified gas/air gas valve. The H fitting con-
tains an orifice which conditions the negative air pressure
controlling the gas valve. This has the effect of allowing
only smooth changes in air pressure to reach the gas valve.
Low Pressure Switch Operation
•
If a call for heat exists and the low pressure switch is
closed already (before the ignition sequence has be-
gun), the IFC will wait 5 minutes. After the 5 minute
delay, and if the LPS is still closed, the IFC will log
and display an error code indicating the low pressure
switch is stuck closed. When the LPS is sensed open,
the IFC clears the error code and resumes normal op-
eration.
If the ignition sequence has begun and the low pressure
switch fails to close within 30 seconds, the IFC logs and
displays an error code indicating the low pressure switch is
stuck open. The inducer continues to run for a total of 5
minutes, at which time the IFC de-energizes the inducer
and then attempts the Calibration routine immediately. If
during the 5 minute interval LPS is sensed closed or call for
heat is removed, the IFC clears the error code and resumes
normal operation.
High Pressure Switch Operation
•
High Pressure Switch action is used to determine the
inducer speed required to achieve the 100% firing rate
of the appliance. The determination is made by the
IFC during the calibration process.
•
The HPS must remain closed during 100% fire opera-
tion. If it opens during 100% fire operation, the IFC
will increase the inducer speed at a rate of 1% per sec
in an attempt to re-close the pressure switch up to
the maximum allowed RPM. If the HPS is re-closed
successfully, the IFC will complete the Heat mode and
perform the Calibration routine on the next call for
heat. If the HPS remains open, the IFC will end the
OPERATION
Heat mode through the Post-purge and perform the
Calibration routine immediately (error code “E9” is
flashed until calibration routine is successful).
•
High Pressure Switch check takes place during the
Calibration routine. If the switch is stuck open or
closed calibration will not be completed and the ap-
propriate error code will be logged and displayed.
Hot Surface Igniter Operation
The IFC energizes a relay to control the line voltage Hot
Surface Igniter. The HSI warm up time will be fixed for all
ignition trials. Both the continuity of the igniter and the
ability of the relay to energize the igniter are continuously
monitored during the Igniter Warm-up and Ignition Activa-
tion Periods.
ECM Motor
An Emerson® UltraTech® four wire indoor fan motor pro-
vides supply air to the conditioned space. This is the same
motor used on previous generation communicating furnaces.
The ECM motor consists of two sections;
1. A motor body containing 3 phase motor windings
2. An electronic control module (end bell).
In the event of a non-operating motor; the following items
should be checked. There are two harnesses which connect
the blower motor to the IFC. The line voltage (5 Pin) har-
ness provides 115 volts directly off of the IFC L1 and neu-
tral terminals on ½ hp ECM motors. On furnaces with ¾ and
1 HP ECM motors, L1 is fed to the motor through an induc-
tor coil. The inductor coil conditions the power supply to
the motor smoothing out spikes and electrical noise. The
low voltage harness is a 4 wire harness that supplies 12
volts DC to terminals 1 & 4 of the motor and communicat-
ing signals on terminals 3 & 4.
T
HE
CONTROL
MODULE
CONTAINS
COMPONENTS
WHICH
CAN
HOLD
AN
ELECTRICAL
CHARGE
FOR
SEVERAL
MINUTES
. B
EFORE
THE
MOTOR
IS
TAKEN
APART
,
IT
MUST
BE
ALLOWED
TO
DISSIPATE
VOLTAGE
BY
WAITING
FIVE
MINUTES
BEFORE
IT
IS
INSPECTED
INTERNALLY
. T
HE
END
BELL
CAN
BE
SEPARATED
FROM
THE
MOTOR
BODY
BY
REMOVING
THE
THREE
SCREWS
WHICH
JOIN
THEM
. O
NCE
THE
SCREWS
ARE
REMOVED
,
THE
INTERANL
HARNESS
CAN
BE
SEPARATED
. T
HE
CONTROL
MODULE
AND
MOTOR
CAN
THEN
BE
INSPECTED
SEPARATELY
.
WARNING
The motor contains three windings of equal resi / -
10%. Resistance between windings is generally less than 10
ohms and will vary between models. To take this reading;
the ohm meter leads are placed in the wiring harness, pre-
viously disconnected from the internal control unit connec-
tor.
Inspect capacitors inside the control unit for bulging or swol-
len caps. The end bell should be replaced if components
appear swollen or bulging. A functioning control unit should
have a phase to phase resistance of greater than 100K be-
tween any two pins. A separated control unit is shown be-
low. To take this reading; the ohm meter leads are placed
in the end bell socket and not in the wiring harness.
