I noticed that the temperature of the air coming out of the vents of my 81 380sl decreases when I'm idling. So I checked to see whether my auxiliary water pump was operating at idle, and it wasn't, evidently because there wasn't any voltage at its two-prong connector.

However, the blower motor and everything else on the car is working fine. So I'm now wondering under what conditions the aux water pump should be operating, and how it gets its voltage.

Thanks in advance for any help anyone can give me on this.

ON a USA car that is controlled by a small temp sensor in the ductwork.

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Thanks for the info, Doc. Are you by any chance referring to the little disc with two wires attached to it on the side of the blower housing? According to the EPC (plate II under Heating and Ventilation for the 107) it's 002 821 18 51.

Over in the SL forum, however, someone stated that a stuck aux water pump can blow out a transistor in the control panel. Before I start tearing into the console, however, I'd like to get a better idea of what I'm looking for?

That is the switch!
Should have power on one side with key on, & if you remove & put it in the freezer for a while it should allow power to the aux w/pump

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator