403
Thermo E+ 120/200/320 4 Heater functions
4.2.2.1 Gradient evaluation
In case of low coolant flow or poor coolant circuit venting
the temperature may quickly increase during heating
operation.
The control unit recognizes the quick temperature
increase and automatically sets the upper switching thres-
hold to a lower value.
The quicker the temperature increases, the lower the swit-
ching threshold for starting the controlled break is set.
In addition, the burner is also switched back on again after
the controlled break at a lower switching threshold.
This prevents residual heat triggering the overheating
protection.
If the temperature rise (temperature gradient) is again
within permissible limits, the thresholds are reset to
normal values immediately (lower threshold 72°C, upper
threshold 82°C).
4.2.2.2 Minimum combustion period
NOTE:
Frequent burning time under 120 seconds may result in
soot build and increased smoke formation.
A minimum burner combustion period of 120 second is
targeted.
For ambient and operating conditions this target is not
always achieved.
In order to achieve the minimum combustion period, the
lower switching threshold is variably adjusted by the
control device.
This process is also called hysteresis adaptation and is
applied during each heating operation.
If the combustion period falls short of the minimum
combustion period of 120 seconds, the lower switching
value is lowered by 1K for the following combustion
process. The upper switching threshold remains as is.
This can be repeated until the minimum combustion
period is reached or the lower switching threshold is
reduced by 5K.
A further lowering is not possible.
Following a combustion process, where the required
minimum combustion period was reached, the lower swit-
ching threshold is raised in steps of 1 K, max. up to the
initial level.
4.2.3 Switching off
Switching the heater off ends the combustion process.
The operation indicator goes off and the purge cycle is
initiated.
The solenoid valve closes, the flame expires, the combus-
tion air fan and circulating pump continue running.
The purge cycle ends approx. after 120 seconds. The
combustion air fan is switched off.
If a malfunction occurs during purge cycle (e.g. flame
detection), the purge cycle may be shorter than 120
seconds.
During purge cycle it is permitted to switch the heater back
on. The burner will restart after a purge cycle time of 30
seconds and subsequent initial cycle time.
4.3 Diagnosis interface and DTT
Diagnosis
The heaters of the Thermo E + series are diagnosable.
The DTT diagnosis can be used to check the heater in the
vehicle using a PC.
For information about connecting your heater to the DTT
diagnosis and how to use it, refer to the DTT Operating
instructions included with the device.
The operating instructions are also available for
Download from the Internet on the Valeo website.
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