190D Fuel Delivery Question

[rnbeals]

1988 190D with estimated 150,000 miles (recently acquired).

I spent some time under the hood and took a couple of photos of the fuel delivery system. I'm trying to decode the logic here:

A - supply from tank
B - inline prefilter (?)
C - unknown gadget with lines that loop along the heater hose
D - lines that loop along heater hose
E - fuel pump
F - fuel filter
G - injection pump

What's going on with gadget "C" and what is the loop along the heater hose?

Thanks!

Rich