This repair shop manual is intended to provide all the necessary information for familiarization with all versions of the Webasto Air Heater Series HL 18 Petrol and Diesel as well as AirTop 18 Petrol and Diesel. The AirTop heaters are an upgrade development of the HL heaters. The manual does not replace the Webasto training course, but is used in many cases as a useful reference guide for initial operation, maintenance, repair, or for removal and installation of the heaters.
Due to the complex technical details, different applications and continuous progress in development, the repair shop manual cannot cover the complete range of possible problems. Additional Webasto publications have to be queried as required:
Because the air heaters' exterior is identical in appearance they are marked on their identification label with the designations "Petrol" or "Diesel". Air Top 18 heaters can be identified by the mat grey finish of their housing, the TRS type by a sticker marked with the words "product in accordance with TRGVS/TRS". The heaters may only be operated with the specified fuel (Diesel version may also use fuel oil EL) and the appropriate electrical power connection Electrical components for specific voltages are marked "red" for heaters operating on 12 Volts and "green" for heaters operating on 24 Volts.
Technical Data of Heaters
Unless limit values are indicated, the following technical data are subject to the normal tolerances for heaters of approx. ±10% at an ambient temperature of +20 °C and at rated voltage.
Air Heaters HL 18 B/D
The heater consists of the heat exchanger, burner, and drive assemblies. The glow plug (6) and the flame detector (7) are secured to the burner head in such a way that they are easily accessible for maintenance. The combustion air fan supplies the required amount of air, which can be adjusted by means of a set screw (refer to para. 6.1 .3) and which flows through ports into the burner tube.
Air Heaters Air Top 18
The glow plug (6) and the flame dete.ctor (7) are secured to the burner head in such a way that they are easily accessible for maintenance. The combustion air fan supplies the required amount of air, which can be adjusted by means of a set screw (refer to para. 6.1.3) and which flows through ports into the burner tube.
Combustion Operation
The heater, now in operation, continues to operate until control voltage at control unit terminal 83 is interrupted. This is caused either by manual manipulation or by the preset operating time limitation of timer P or by the room thermostat. Note: Depending on the heat requirement the heater may remain in "combustion" or "control idle" (means heater off) condition for some time.
Start after Control Idle
In case the heater is operated with a room thermostat, a new start cycle is automatically initiated as soon as the room temperature drops below the switching threshold. The operation indicator light is illuminated during the complete control idle period. Heaters HL 188/D (with glow plug) always start in full load operation. Air Top haters (with glow pin) start after an initial breakaway in part-load and then switch to full-load after 20 seconds. After a minimum full-load operating time of 60 seconds, the part-load operation is resumed depending on the switch position of the room thermostat.