T
HERMO
90 / 90 S
5TROUBLESHOOTING
5-1
5. Troubleshooting
5.1 General
This section describes troubleshooting procedures for
the Thermo 90 and Thermo 90 S coolant heaters.
CAUTION
Troubleshooting requires profound knowledge about
structure and theory of operation of heater components
and may only be performed by skilled personnel.
In cases of doubt refer to Sections 2 or 3 for functional
interrelations.
CAUTION
Troubleshooting is normally limited to the isolation of
defective components.
The following defects are not included in the
troubleshooting procedures. Before troubleshooting,
check for and eliminate these defects:
- fuel supply (plugged fuel filter or no fuel)
- corrosion on battery terminals
- blown fuses
- corrosion on electrical wiring and fuses
- corrosion on connectors
- loose contact on connectors
- wrong crimping on connectors
- shut-down initiated by temperature limiter
After any correction of a failure a functional test has to be
performed in the vehicle; before switching the heater off
and on again.
5.2 General Failure Symptoms
The following table (Fig. 5-1) lists possible, general
failure symptoms.
NOTE:
In many cases the probable cause of failure may be the
burner. Perform a visual inspection according to 5.4.
Failure Symptom Probable Cause Remedy
Heater switches No combustion after start or Control unit goes into error lock-out.
off automatically repeat start Switch heater off and on again.
Flame extinguishes during operation If a no-heating condition persists
contact your Webasto service agent.
Heater overheats due to lack/loss of Replenish coolant.
coolant After cool-down of unit, push button
of temperature limiter before
reactivation or replace temperature
limiter.
Low voltage condition for more than Check fuses, connections and charge
20 seconds state of battery.
Switch-off caused by temperature After cool-down of unit, push button
limiter of temperature limiter before
reactivation or replace temperature
limiter.
Fig. 5-1 General Failure Symptoms
