auxilliary water pump question
 

I'm troubleshooting my off and on heating, and have already replaced the monovalve piston. Through reading here, I've arrived at the auxilliary water pump as a possible culprit.

Question: (w123 300TD '85)
1. Under what conditions does this pump operate? (heat on, car at op temp, thermostat open, which dash switches, etc?)

I can test it by feeling for vibration I assume, as it's mounted in a rubber sleeve. So far, it feels dead. However, I hooked up a known working used pump to the harness and I can't get it to work either... so when does this puppy turn on?

Thanks!
k

A recent thread noted that a poor electrical connection at the monovalve can cause on/off heating problems. I cleaned mine today hoping that it might solve my problems. I've considered the fact that it might be poor connections in the dash control unit. I just hooked up a spare pump to a battery and I can definitely hear it run (without fluid in it) but can't feel much.

Yeah, I cleaned those connections when I put in the rebuild kit yesterday. But I can't seem to get power to the aux. pump. I hooked up the multi-meter to the harness, and there is very little juice if any getting there- so I want to know how I can be sure that I've got the conditions such that there should be power to that harness, and the pump it powers.

How is Kuan contending that
A is taller than B
B is taller than C
therefore A is taller than C
is false? especially when he submits that the premises are both true?

Operates in defrost all the time, and at idle under certian conditions, it will cause your climate control to fry if inoperative, good luck

This may be a silly question, but have you checked the fuse that supplies juice to the pump?
On my SDL it is #5 and it also powers the A/C Compressor Clutch.

What is it about the idle condition that causes the auxiliary water pump to operate? Is it the water flow rate somewhere in the system or the actual engine RPM or something else entirely? Would help to know exactly what criteria need to be met for that device to operate. Also, does anyone know what part of the ACC main board goes if the auxiliary pump seizes up? Thanks for any ideas.

all fuses good, I did think of that- not silly at all. I might just replace some of the old ones though for good measure, and clean all of the contacts properly to make sure that's not part of the issue.
Tomorrow I'll see if I can power up the known working pump on the defrost function... fingers crossed.
k

Hmmm.
 

RULE #1. when having electrical problems, install all new fuses.
RULE #2. when having electrical problems, install all new fuses.
RULE #3. when having electrical problems refer to rule #1. and #2.

You can't trust old corroded fuses.

I replace my fuses and bulbs every four years, even on domestic beaters, very rare for me to have any electrical issues.

You need to do some searches on this topic, there are hundreds of posts.

whunter,

And when you have engine problems, do you replace your engine.

I don't ever replace my fuses or bulbs unless they burn out and I rarely have electrical problems. One time I did have some fuses that were corroded and not making an electrical connection. The problem was that the fuse box cover was leaking and road salt was getting into the fuse box. So that is what I fixed. Problem solved: I fixed what was broken.

So your statement that you rarely have electrical doesn't prove much. How did you determine that 4 years was the optimum time? Why not 3 years, or 2 or 1?

If it ain't broke, don't fix it.

P E H

Answer:
 

The oxidation rate of aluminum from OEM durability testing.
The OEM warranty claims index.
Also from 30 years experience as a master mechanic.
Changing the fuses gives a solid base line for further diagnosis.

We have had this discussion before, thought we agreed to not agree.

I had the same on-off heat problem on my 300SDL. As part of some major engine work I replaced the Aux. Water Pump. That seemed to solve the problem. No more heat surges. Perhaps it was a bad connection that I restored during the R&R. I always use dialectric greese on my connectors when reconnecting. But then again maybe it was the pump. By the way the old pump did operate when I attached it to a battery. So maybe it was intermittant.

Ok.... update. inspected fuses, all were fine, and I cleaned the contact points of the terminal in question and gave a new one just for grins.

On the '81, I had wife turn the defrost off and on so I could feel the aux pump working- (slight but noticeable vibration in the rubber housing)

Tried the same with the '85, and no dice. Not with the known good used one I've got or the one installed in the car.

Tried getting a multi-meter reading on the wire harness plug and it was not getting much of anything if at all, and no difference off or on for the defrost.

Also, an audible click could be heard when turning on the defrost, and it was evident the idle changed ever so slightly.

goal: working aux pump!

? help!
Thanks!!!
k

so you've determined the controller is not sending the current necessary to operate the pump. Measure the CURRENT that it does send by putting your multimeter inline and provide a very good ground to the other terminal and check the connectors very carefully. You should then be able to isolate it between connectors, wires to the pump or the controller.

When my aux pump was not working the only problem was a lack of heat at idle. Not an immediate lack, just a slow cooling off if you are just sitting idling in park. I ended up with another pump from a boneyard and it has a relay with a diode to take the load off the climate control unit so that if the pump ever goes bad it doesn't take out the CC unit. RT