Auxiliary Water Pump Question

[daimlerdude]

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.

[meltedpanda]

the purpose of the aux water pump is to continue the flow of coolant when at idle , your appears not to be working . IIRC it runs all the time or most certainly when the heat is on

[Strife]

Originally Posted by meltedpanda

the purpose of the aux water pump is to continue the flow of coolant when at idle , your appears not to be working . IIRC it runs all the time or most certainly when the heat is on

It is perfectly OK to apply +12 or -12 to the motor directly to see if it spins.

They can get corroded, dry of oil and stop working; I successfully revived one. A good one, believe it or not, will spin on a 9V transistor radio battery.

Be aware that earlier models (maybe 82-85? or maybe 82-84?) were notorious for blowing out the power transistor in the pushbutton control when the motor failed. I don't know how the ASCII (81) system handles this.

[daimlerdude]

Originally Posted by Strife

It is perfectly OK to apply +12 or -12 to the motor directly to see if it spins.

They can get corroded, dry of oil and stop working; I successfully revived one. A good one, believe it or not, will spin on a 9V transistor radio battery.

Thanks for the tip. I applied current from a 9V to the pump and it spun freely.

Originally Posted by Strife

Be aware that earlier models (maybe 82-85? or maybe 82-84?) were notorious for blowing out the power transistor in the pushbutton control when the motor failed. I don't know how the ASCII (81) system handles this.

Since the motor spun freely, I'm assuming that it didn't seize up and blow out the transistor you mentioned. By any chance, are you referring to the little disk/temperature switch on the side of the blower motor housing?

According to the 107 manual (on-line at http://www.startekinfo.com/StarTek/outside/11883/PROGRAM/Climate/83-690.pdf) that switch should turn the aux pump off when the temp of the air in the blower motor hits 79 deg. F and on again when it gets to 61 deg. F. So, I'm now assuming that that switch is the problem, as MB Doc suggested in the Tech Forum.

According to him, there should be power to the switch when the key is on, and current flowing through it when the switch is cold. So I'm going to hold an ice cube on it to see if the pump comes on. If not, and the switch is getting current, I'll assume that it's bad.