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1999 mercedes m320 , Vin 4JGAB54EXXA141286 , 107,000 miles
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69 Posts
Discussion Starter #1
1991 190E, 2.3- Can the Auxilliary Water Pump be running and still be defective, still working on my heating problem.
 

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92 190E 2.3 SOLD, 91 420SEL, 95 C280
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488 Posts
If the impeller (the part that pushes the water) is broken, the pump will run but the water won't be moving.

One thing to check is whether the PO placed something in one of the lines to block the flow. I posted in a previous post where the PO of my 201 stuffed a lug bolt into the hose from the water pump to the aux pump instead of simply replacing the defective heat valve.

Are the hoses behind the firewall that feed the heater core getting hot? if they are then perhaps your heater core is all clogged up.

Good Luck
 

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1999 mercedes m320 , Vin 4JGAB54EXXA141286 , 107,000 miles
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69 Posts
Discussion Starter #3
I took out the glove compartment and the metal return line is getting very hot. I guess this narrows it down to the heater core being clogged or flaps not working correctly. If its the heater core is there any way to clean it out or does it have to be replaced? I noticed if I turn the air supply off (off button) I get air flowing through the side and center vents when driving down the road. I'm thinking this could be my main problem. Anyone have similar problems with your heating system?
 

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92 190E 2.3 SOLD, 91 420SEL, 95 C280
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488 Posts
First, take some time to educate yourself regarding the vents. the center vents above the heater control switch will ALWAYS blow cold, that is the design. The heat will come from the side vents, foot well, and defrost at the windshield.

If you have warm water getting through your heater core then I would not suspect that as your problem. More than likely it has to do with your flaps, which are vacuum operated. when one fails though it defaults to a heating setting, so if you are not getting warm air I would think there may be some obstruction not allowing the proper vents to open and let the air go where it should.

Another item to test is the actual heater control unit, if the temp wheel isn't being read then it may not know that you are wanting heat.

If you close the center vent and run the fan on the max heat setting do you get any warmth from any of the vents?

Incidentally, you can clean the heater core by doing a cooling system flush, search on here for it and you will find threads talking about using a citrus acid flush to clean out the cooling system, it may be useful or not.
 

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'93 190e 2.3 171K miles, '95 Geo Prism 160K miles, '96 F250 7.5L 104K miles
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140 Posts
if you're certain the heater core RETURN line is hot, then coolant is flowing through the core and the core is not plugged. the vacuum motors ( 3 i think) that control the flaps do fail, unfortunately, replacing the motors (at least the one that controls the hot/cold air blend and its associated position potentiometer) requires taking the dash cover out. of course, the control unit could be bad. the only way i could figure to diagnose my problem was to substitute an alternate vacuum source (eg an electric or hand vacuum pump) for the engine vacuum and then monitor vacuum change and listen for vacuum motor operation as the various control switches were pressed or the temp control knob rotated from max to min to max. there is a vacuum reservoir on the cabin side of the vacuum circuit check valve ( CV under the hood, near firewall, LH side). a vacuum gauge T'd to the vacuum source is a good monitor of how the control system and vacuum motors are working. with the OFF control switch IN, the aux vacuum source should be able to create a maximum vacuum (>10"Hg) and that value should hold steady after pumping has stopped. if it does not hold, there is a leak which must be corrected before proceeding (note that a zero vacuum allows the coolant control valve to open for maximum flow to the heater core). assuming the vacuum holds, then with the ignition on and engine off, press each control switch while listening for motor/flap change watching the vacuum gauge, the vacuum level should decrease slightly as different vacuum motors (including the coolant flow control valve) engaged. if the vacuum goes to zero (aux vacuum pump off), the motor has a diaphragm leak and needs replacing. if the vacuum doesn't change at all, then the control is not working. rotating the temp control knob max-min-max should cause a slight vacuum decrease as the blendair vacuum motor operates.
 

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1996 Volvo 855GLT, 1993 MB 190e 2.3 8v, 1998 Subaru Outback SUS, 1991 BMW 525, 1998 MB C230
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it could also be a bad vaccum control mechanism or a bad control unit. i think theres a thread somewhere that shows you how to test the temp control system.
 
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