Electric heat booster

[Aleksey]

Team,

An issue has been identified with the electric heat booster. Attempts to locate a fuse have been unsuccessful, despite online references suggesting fuse 75. No such fuse exists in the system. Is it possible the unit is wired directly? Are there specific operational parameters required for activation? Some sources indicate functionality is limited to cold weather conditions with the engine and AC engaged.

Guidance on initial troubleshooting steps would be greatly appreciated.

 

[DSM10000]

Welcome.

Letting us know the model of the vehicle would help with an answer

 

[mersum1es]

Usually those are large fuses, found in pre fuse box or somewhere separate in engine bay depending on which car,
Edit: If its W204, pre fuse box 150A fuse number 103...

 

[Trickythemerc]

The heater booster is a common failure as is the auxilliary water pump. Both these parts have failed on my 220 CDI, the water pump I have done but held off on the heater booster for now.

 

[Petrol Pete]

Can someone explain what we are discussing here please ? Is it the residual heat function that uses the warm water in the engine block to heat the cabin with the engine off ?

 

[DSM10000]

Can someone explain what we are discussing here please ? Is it the residual heat function that uses the warm water in the engine block to heat the cabin with the engine off ?

No idea as the OP has not provided accurate information as yet.

 

[Supernoodle]

I would think we're talking about a PTC (positive temperature coefficient) electrical heater. It's used to heat the cabin air before the the engine is up to temperature.

 

[Trickythemerc]

I think it will be the pre heat to aid defrosting ? Big lump of a thing on the block that helps bring the coolant up to temp before the stat opens.