Aux Water Pump Inop; No Power at Plug - Page 2

rrgrassi · #16 01-15-2010, 05:07 PM

Quote:

Originally Posted by tobybul

just want to clarify. the CCU you are referring is the one connected to the pushbutton unit?

(Assuming what you are saying is true, i too have played with this. i replaced the CCU with a known good one and the same thing happens. Maybe the CCU attached to the PBU I am referring to is different from the CCU you are referring to?)

I think some people interchange the PBU (Push Button Unit) and the CCU (Climate Control Unit), so it gets confusing.

Brian Carlton · #17 01-15-2010, 05:13 PM

Quote:

Originally Posted by diesel85

Thanks for the info Brian. One more question. When should the aux pump engage?

From memory, in cold climates, it is on in every button position except the far right (system off).

Brian Carlton · #18 01-15-2010, 05:15 PM

Quote:

Originally Posted by tobybul

Brian, many seem to refer to the CCU also as the push button unit. Are you doing the same thing or is there another unit besides that and where is it located?

Many refer to the "climate control unit" or "CCU" as the pushbutton unit. They would be using incorrect terminology for the same device.

tobybul · #19 01-15-2010, 11:19 PM

Thanks. So is the K1 relay referred to above the CCU/PBU?

Jeremy5848 · #20 01-16-2010, 12:02 AM

The relay is part of the push-button unit.

micalk · #21 01-16-2010, 01:37 PM

Quote:

Originally Posted by fdanielson

After much consulting of the wiring diagrams I found that the K1 relay in the CCU controls the aux pump and the footwell flaps.

Haven't checked regarding footwell flaps, but as far as aux pump goes I agree... According to my read on the schematics, K1 in the PBU/CCU controls the aux pump. When K1 is off, the aux pump is on. Aux pump is on (K1 is off) when Defrost is selected and the temp wheel is not in the 'Min' position. It is also on when in the other three operating modes (EC, Normal, AC) as controlled by the Temperature control unit. The Temp Control unit would remove/apply ground to the K1 relay as it deems fit. Max temp may signal to the Temp Control unit to have the pump on all the time, but this can't be determined by the schematics. The bottom line is that the pump should be on when in defrost and temp wheel is not Min.

You should be able to check the wiring and CCU/PBU connections with the key in the off position. Remove the connector from the pump. Put the Temp Wheel in Min position. Using an ohmmeter, check the resistance between ground and the 12V terminal on the CCU/PBU end of the pump connector. You should see no resistance (there's no diode in this circuit). Another check is to move the Temp wheel off the Min position and place one ohmmeter lead on Fuse F8 (F8 is hot in the run position, so it should be open when the key is off) and the other lead on the 12V side of the pump connector. This circuit contains a diode and a resistor, so if you get an open then reverse the ohmmeter connections and you should see some resistance. If you still see an open, chances are your PBU is the culprit. Both these checks go through the contacts of the K1 relay in the CCU/PBU.

Disclaimer: This is according to MB schematics, I haven't tried this or tested this. YMMV.

diesel85 · #22 01-16-2010, 01:38 PM

Can anyone give me more information as to what to look for on the CCU board? I hear about re-soldering the board but what exactly am I looking for? I can see the underside of the board by removing the cover. Do I need to remove the entire board from the unit? Can anyone provide pictures or a video link to repairing the CCU?

micalk · #23 01-16-2010, 01:49 PM

Quote:

Originally Posted by diesel85

Can anyone give me more information as to what to look for on the CCU board? I hear about re-soldering the board but what exactly am I looking for? I can see the underside of the board by removing the cover. Do I need to remove the entire board from the unit? Can anyone provide pictures or a video link to repairing the CCU?

If you have the PBU out, check the connection from Connector 2 Pin 10 to Connector 2 pin 2. This should be a direct connection with the Temp Wheel in the Min position. Also check Connector 2 Pin 10 to Pin 12. This has the resistor and diode in the circuit so you may have to reverse the ohmmeter leads to see the connection. I'd be very interested in your results.

micalk · #24 01-17-2010, 08:54 AM

Alright, I checked out a PBU out of an 84 300D. This PBU had issues when I pulled it out, and ohmmeter values to the connectors would change as I flexed the sides, so I'm sure that was one of the problems. First, Connector 2 is the 12 pin connector on the Temp Wheel side. It appears that there is no diode and resistor in the path for energizing K1 (Connector 2 pin 12 to Connector 1 pin 3) which kinda makes sense since this is also in the path to the aux pump. It would also appear that the Temp Wheel has circuit has a diode and resistor in the path. So the schematic I am using is questionable at best. It's a genuine MB pdf - crappy pictures and all, but I'm not sure where it came from. It's in a separate folder from my manual files. The name on it is 83-acc.pdf.

Anyway, the test that should for sure work is from the fuse to the hot side of the connector with the key off. According to the CCU in my hand, anyway. Again, YMMV.

tobybul · #25 01-17-2010, 11:44 PM

Here's what the FSM says.... lets see if we can figure out what it means....

The FSM also says that at 22*C and up, the auz water pump should be running whenever buttons a to d are depressed. Its not running when e is depressed.

#26 01-17-2010, 11:47 PM

Quote:

Originally Posted by tobybul

Here's what the FSM says.... lets see if we can figure out what it means....

It seems to say that the aux pump should be running whenever the lower vents are open.

tobybul · #27 01-18-2010, 12:06 AM

Makes sense. Its also whenever buttons a to d are depressed and wheel is at 22*C or higher. The wheel does not have to be all the way at max heat for the pump to turn on.

Jeremy5848 · #28 01-21-2010, 12:32 AM

Finally found what I was looking for in the 1986 W124 "Introduction into service" manual (this has all the information on the W124 as a new model). On page 283, it says that "the auxiliary coolant pump (M13) . . . runs in the heating mode, when the monovalve is either completely open or cycling."

I infer from this that on a hot day, when you are using the a/c, the aux pump will not be running. The aux pump gets +12 Volts from Fuse 7 and is grounded through the Push-Button Unit, which turns it on and off as needed.

Jeremy

tobybul · #29 01-21-2010, 06:45 AM

Quote:

Originally Posted by Jeremy5848

Finally found what I was looking for in the 1986 W124 "Introduction into service" manual (this has all the information on the W124 as a new model). On page 283, it says that "the auxiliary coolant pump (M13) . . . runs in the heating mode, when the monovalve is either completely open or cycling."

I infer from this that on a hot day, when you are using the a/c, the aux pump will not be running. The aux pump gets +12 Volts from Fuse 7 and is grounded through the Push-Button Unit, which turns it on and off as needed.

Jeremy

Thanks..... thats probably how the W123s also operate..... which still begs the question - what component or part causes the pump not to get power when it is suppose to get power? Is it a bad component inside the PBU? The K1 relay perhaps?

Jeremy5848 · #30 01-21-2010, 12:14 PM

Quote:

Originally Posted by tobybul

Thanks..... thats probably how the W123s also operate..... which still begs the question - what component or part causes the pump not to get power when it is suppose to get power? Is it a bad component inside the PBU? The K1 relay perhaps?

Unlike the W124 CCU, the W123 version sends +12V to the aux coolant pump from the PBU. The "other" end of the aux pump is grounded. The relays in the PBU in my schematic aren't labeled but it is the first one, so let's call it "K1." The wire (black-red-violet) to the aux pump is pin 10 in one of the two big plugs that attach to the sides of the PBU but my schematic doesn't identify which of the two plugs. One of the diagrams calls it the "left" terminal, that is, the one on the side where the temperature dial is. So try that one first. The plastic plugs should have their pins numbered.

To help you figure it out, I see that pin 10 in the other (right side) plug is a black-red wire. So look for a black wire with a red stripe and violet rings or blobs ever so often. That wire goes to the aux pump and at the very least should have +12V on it if you press the Defrost button.

If you do not get +12V at that pin 10 when you press the defrost button, then I recommend opening up the PBU and checking all of the relay contacts for corrosion. While you're in there, look for burnt PC-board traces. That can happen if the aux pump freezes and draws too much current, since the aux pump is not fused and the PBU circuitry is not protected (this is a change that was made in the W124 PBU). My W123 PBU had that exact problem -- I had to take it apart and run wires to bypass the burnt traces.

I'll try to post the schematic later today from my W123 air conditioning manual..

Jeremy

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