An auxiliary heater like the Webasto Thermo 90 S keeps the cab or coolant circuit warm on cranes and heavy vehicles, so the operator isn't climbing into a frozen machine and the engine starts easier. When it quits, the person holding the wrench needs workshop-level information, not guesses. That's usually a fleet mechanic or shop tech fixing it in-house, or someone working on a unit that arrived with no paperwork.
What this manual helps you do
- Diagnose a no-start or lockout using the troubleshooting section.
- Verify heater operation step by step with the functional tests.
- Trace wiring faults with the circuit diagrams.
- Follow the servicing procedures during routine work on the unit.
- Replace worn or failed parts using the repair section.
Who this is for
A crane service technician, rental fleet mechanic or independent repair shop that has a Thermo 90 S on the bench or in the machine. It's also useful for plant maintenance staff who look after heaters on their own equipment.
FAQ
Q: What do I receive and how is it organised?
A: You get the set of 3 PDF files, 162 pages in total, in English and German. The main manual is publication 1301496B02_DE (55 pages), with Manual 2 (52 pages) and Manual 3 (55 pages) alongside it.
Q: Which heater does it fit?
A: It's the Thermo 90 S and ST Workshop Manual, so it covers both the Thermo 90 S and the Thermo 90 ST.
Q: How does it fit the job I'm doing?
A: It's the complete workshop manual. You'd expect to find the introduction, general description, functional description, technical data in standard and metric measure, troubleshooting, functional tests, circuit diagrams, servicing and repair, which is the order most heater jobs follow.
Open it before you pull the heater apart, and you'll have the diagnosis, test and repair steps in one place.
Click here to view the preview (PDF)
Models covered by this manual
This service manual is also used for one further Heater model: Thermo 90 ST. Check the model and serial number on your data plate before ordering.
📘 Show Index
Table of Contents:
- Publication 1301496B02_DE (55 pages)
- Manual 2 (52 pages)
- Introduction
- Scope and Purpose
- Meaning of Warnings, Cautions and Notes
- Additional Documentation to be used
- General Description
- Combustion Air Fan
- Heat Exchanger
- Temperature Sensor
- Functional Description (Fig.3-1)
- Switch-on
- Heating Operation
- Control Operation
- Technical Data (Standard Measure)
- Technical Data (Metric Measure)
- Troubleshooting
- General
- General Failure Symptoms
- Failure Symptoms after Switch-off upon Failure
- Functional Tests
- General
- Adjustments
- Components Testing
- Circuit Diagrams
- Servicing
- General
- Work on the Heater
- Work on the Vehicle
- Repair
- General
- Disassembly and Assembly
- Manual 3 (55 pages)
- Introduction
- Contents and purpose
- Meaning of signal words
- Additional documentation to be used
- General description
- Combustion air fan
- Heat exchanger
- Temperature sensor
- Function description
- Switching on
- Heating mode
- Control mode
- Technical data
- Troubleshooting
- General
- General fault indications
- Fault indications on fault lock-out
- Function tests
- General
- Settings
- Testing individual components
- Circuit diagrams
- Service work
- General
- Work on the heater
- Work on the vehicle
- Repair
- General
- Dismantling and assembling
- Packing, storage and shipment
- Sequence of functions
- General fault indications
- Fault indications on fault lock-out
- Visual check, burner back wall
- Visual check, pilot flame outlet opening
- Visual check, complete burner
- System circuit for Thermo 90 S, 12 and 24 V, with standard clock
- circulating pump control
- System circuit for Thermo 90 S-ADR, 24 V, with switch
- System circuit for Thermo 90 S-ADR, 24 V, with switch without power take-off
- System circuit for Thermo 90 ST, 12 and 24 V, with standard digital timer
- System circuit for Thermo 90 ST-ADR, 24 V, with switch
- System circuit for Thermo 90 ST-ADR, 24 V, with switch without power take-off
- Specimen installations for heater in a truck
- Fuel supply
- Webasto fuel extractor
- Fuel extraction from the plastic tank (extraction through tank drain screw)
- Fuel extraction from the plastic tank (extraction through tank fitting)
- Pipe/hose connection
- Metering pump, installation position and attachment
- Exhaust pipe opening, installation position
- Electrical connections (Thermo 90 S)
- Changing the circulating pump
- Changing the temperature limiter and temperature sensor
- Changing the combustion air fan
- Changing the burner, flame monitor and glow plug
- Changing the burner head
- Contents and purpose
- Meaning of signal words
- Additional documentation to be used
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