It is a misconception that all Sprinters came with some sort of diesel powered auxiliary heater or a booster heater. This is caused by MB or Dodge literature that would call something out as standard equipment when it was not.

My Sprinter, in addition to the normal engine heated coolant heater came with then option, HH2, and electrically powered hot-air auxiliary heater. It is also known as AEHM module and Heater Unit PTC) I would think that many other Sprinters were delivered in the same configuration. There are no controls for this heater and it works automatically based on ambient temperatures. Being in California, the temps have not been low enough (yet) for me to confirm that it works. The owner’s manual (under Sprinter resources) describes it like this:

The vehicle is equipped with an electrically powered heater booster system. The heater booster system ensures that the vehicle interior is heated up as quickly as possible during the engine’s warm-up phase. The heater booster system switches on automatically as required.

By referring to it as a “heater booster system” the OM adds to the confusion.

From the Special Equipment book (under Sprinter resources) which calls the option HB9 (and says it is standard on all models), we have a description of how the heater works:

The heater booster consists of radiator elements (fins) which are fitted with PTC (Positive Temperature Coefficient) resistors and are held together in a mounting frame by spring clips. When an electric voltage is applied to the heater elements, an electric current flows through the PTC resistors, which heat up. The fins absorb the heat and radiate it to the passing air. As soon as the engine is running, the electric heater booster steadily increases its power from 0 to 100% in the space of 28 seconds. The heater booster is situated in close proximity to the air outlets, to keep heat losses to a minimum. The warmed air is circulated into the interior via the vehicle heater/blower system.

• Switch-on conditions:
  Coolant temperature < 80°C (176°F) and ambient temperature < 10°C (50°F).
• Switch-off conditions:
  Coolant temperature > 80°C (176°F) and ambient temperature > 13°C (55°F).

The heater is located behind the center panel in the middle of the dashboard. (basically below the radio). I do not know yet what AC/Heater switch configeration effects it. Does it only work when the AC compressor is on? Does it work with the AC compressor is off?