Conditions Effecting Furnace Operation - Trane UHMB060ACV3VB Installer's Manual

CONDITIONS AFFECTING FURNACE
OPERATION
NOTE:
CONTINUOUS fan mode during COOLING operation
may not be appropriate in humid climates. If the in-
door air exceeds 60% relative humidity or simply feels
uncomfortably humid, it is recommended that the fan
only be used in the AUTO mode.
1. EXCESSIVE COMBUSTION PRESSURE (WIND
IN EXCESS OF 40 M.P.H.) VENT OR FLUE
BLOCKAGE
On a call for heat, the Variable Speed Draft Inducer must
first ramp up to speed and close the Pressure Switch
before the Ignition Sequence is allowed to begin. If the
Pressure Switch does not close, the Motor will ramp up
to maximum speed and continue to operate at maximum
speed for about one minute. After one minute, the Inte-
grated Furnace Control will turn the Motor off for about 30
seconds then back on in an attempt to reestablish proper
operation. This condition is indicative of a highly restricted
or blocked inlet or outlet Vent Pipe or a failed Pressure
Switch.
If pressure against induced draft Blower outlet becomes
excessive, the Pressure Switch will open. If the Pressure
Switch is open for more than 3.5 seconds, the Variable
Speed Draft Inducer will speed up and attempt to close
the Pressure Switch.
If the Pressure Switch is not closed within 12 to 15 sec-
onds or if the maximum speed of the Motor is reached,
the Draft Inducer sends a Fault Signal to the Integrated
Furnace Control. If the unit is operating in high heat, an
Inducer Fault will cause the Furnace control to transition
the system to medium heat and it will operate there for
10 minutes before attempting to run again in high heat.
If the unit is operating in medium heat, an Inducer Fault
will cause the Furnace control to transition the system to
low heat and it will operate there for 10 minutes before at-
tempting to run again in medium heat. If the unit is oper-
ating in low heat, an Inducer Fault will cause the Furnace
control to shut the system down and wait 30 seconds be-
fore attempting to reestablish operation in low heat.
2. LOSS OF FLAME
If loss of flame occurs during a Heating Cycle, or flame is
not present at the sensor, the Integrated Furnace Control
(IFC) will close the Gas Valve. The Integrated Furnace
Control will then recycle the Ignition Sequence. If Ignition
is not achieved, it will shut off the Gas Valve and lock out
the system.
3. POWER FAILURE
If there is a power failure during a Heating Cycle, the
system will restart the Ignition Sequence automatically
when power is restored, if the Comfort Control still calls
for heat.
4. GAS SUPPLY FAILURE
If a gas supply failure occurs during a Heating Cycle, the
system Integrated Furnace Control will recycle the Igni-
tion Sequence, then if Ignition is not achieved, the Inte-
grated Furnace Control will shut off the Gas Valve and
lock out the system.
5. INDUCED DRAFT BLOWER FAILURE
Please refer to the "Communicating Controls Service
Manual," publication number 34-4093 (latest revision), for
diagnostic assistance.
6. CONDENSATE DRAIN BLOCKAGE
If the condensate drain is blocked, either by debris, im-
proper draining, or by freezing condensate, the pressure
switch will receive a signal warning of the accumulation
of condensate in the heat exchanger assembly. The pres-
sure switch contacts will open and remain open, not al-
lowing unit operation. The unit will not operate until the
condensate drain has been cleared, and the condensate
flows freely.
7. RESET AFTER LOCKOUT
When the Integrated Furnace Control has shut the sys-
tem down and gone into lockout, the system may be
manually reset. The system can be reset by turning the
system power off.
8. RESET AFTER BURNER BOX LIMIT SHUT- DOWN
BURNER BOX TEMPERATURE LIMIT DEVICE
All models are equipped with a Manual Reset Tempera-
ture Limit located on the Burner Box. In case of excessive
temperature, the Limit will open and cause the circuit to
open which shuts off all flow of gas. If the Furnace shuts
down check the Burner Box Temperature Limit Switch. It
is located on the bottom of the Burner Box. The Vent and
Combustion Air Inlet terminations must first be checked
for blockage. If blockage exists, clear the problem and
then the Reset Button may be depressed. If there is no
blockage of the terminations, do not reset the Burner
Box Limit Switch. A qualified service professional
should be called to determine the problem and reset
the Limit Switch.
18-CD30D1-12
Installer's Guide
53