Fenwal 35-65 Series Manual page 2

SEquENCE OF OPErATION / FLAmE rECOvEry/ SAFETy LOCkOuT
power-up / standBy
35-66 with Full-time power (r Models only):
Upon applying power (24 volts) to the R terminal, the control will
reset, perform a self-check routine, flash the diagnostic LED for a
second and enter the thermostat scan state.
Call For Heat
35-65 & 35-66 without Full-time power (r terminal):
When a call for heat is received from the thermostat supplying 24
volts to the W terminal, the control will perform a self-check routine,
flash the diagnostic LED for a second and begin the safety timing
sequence. After an optional "pre-purge" period, the hot
surface ignitor is energized for a heat-up period, followed by the
gas valve for the "trial for ignition" (TFI) period.
Call for Heat - 35-66 Models:
In addition to the self-check routine described above, when a call
for heat is received from the thermostat supplying 24 volts to the
W terminal, the control will check the pressure switch for normally
open contacts. The combustion blower is then energized and,
once the pressure switch contacts close, an optional "pre-purge"
period begins. After pre-purge, the hot surface ignitor is energized
for a heat-up period, followed by the gas valve for the "trial for
ignition" (TFI) period.
Ignition - 35-65 Models:
When the flame is detected during the TFI period, the ignitor is
de-activated and the gas valve remain energized. The thermostat
and main burner flame are constantly monitored to assure that the
system operates properly. When the thermostat is satisfied and the
demand for heat ends, the gas valve is immediately de-energized.
Ignition - 35-66 Models:
When the flame is detected during the TFI period, the ignitor is
de-activated and the gas valve and combustion blower remains on.
The thermostat, pressure switch and main burner flame are
constantly monitored to assure that the system operates properly.
When the thermostat is satisfied and the demand for heat ends,
the gas valve is immediately de-energized, the control senses the
loss of flame signal and initiates an optional "post-purge" period
before de-energizing the combustion blower.
FaIlure to lIgHt - loCkout
single try Models:
Should the main burner fail to light or the flame is not detected
during the TFI period, the control will lockout. The gas valve
will be turned off immediately. For 35-66 models, the combustion
blower will be turned off following an optional "post-purge"
period. With the 1 hour reset option, if the thermostat is still
calling for heat, the control will automatically reset and attempt
a new TFI sequence after one hour.
Page 2 Series 35-65, -66 HSI Control with 120/240 Field Selectable Line Voltage
FaIlure to lIgHt - loCkout
Multi-try Models:
Should the main burner fail to light or the flame is not detected
during the first TFI period, the gas valve is de-energized and
the control performs an optional "inter-purge" delay before
attempting another TFI period. The control will attempt 2
additional TFI's periods before locking out. In lockout, the
gas valve will be turned off immediately. For 35-66 models, the
combustion blower will be turned off following an optional
"post-purge" period. With the 1 hour reset option, if the
thermostat is still calling for heat, the control will automatically
reset and attempt a new TFI sequence after one hour.
lockout recovery:
Recovery from lockout requires a manual reset by either
resetting the thermostat or by removing the 24 volts for a period
of 5 seconds.
loss of Flame - re-igntion:
If the established flame signal is lost while the burner is operating,
the control will respond within 0.8 seconds. The gas valve is de-
energized immediately and a new TFI sequence begins. If the
burner does not relight, the control will lockout as previously
described in the "Failure to Light - Lockout" section. Multi-try
models will make 2 more attempts to light the burner. If flame is
re-established, normal operation resumes.
CoMBustIon aIr Flow proBleMs
35-66 Models only:
1. Combustion airflow is continually monitored during the ignition
sequence by the pressure switch (PSW terminal). If the pressure
switch contacts remain closed for 30 seconds at the start of the
ignition sequence without an output signal to the combustion blower,
an airflow fault is signaled and the control will remain in this fault
mode with the combustion blower off. If the pressure switch
contacts later open while there is still a call for heat, the control
begins the pre-purge period followed by a normal TFI sequence.
2. If the pressure switch contacts remain open for more than 30
seconds after the combustion blower output (F1 and F2 terminals)
is energized, an airflow fault is signaled and the control will remain
in this fault mode with the combustion blower on. If proper airflow
is later detected from the pressure switch input (PSW terminal),
the control begins the pre-purge period followed by a normal
TFI sequence.
3. If the airflow signal is lost while the burner is firing, the control
will immediately de-energize the gas valve and an airflow fault is
signaled. The combustion blower will remain on for the post-purge
period and the control continues to monitor the PSW input waiting
for airflow to return. If proper airflow is detected during the
post-purge period, a normal TFI sequence begins preceded by
any pre-purge period. If not, the control will enter a lockout
condition with the combustion blower off.
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