poor flow
 

Hey guys.Hopefully you can help.The heater-a/c on my 89 300e 3.0l doesent have as much output(flow) as it did.The temp is ok but not much air volume.It also doesent seem to change much from low speed to high speed.
Any input would be appreciated.Thanks.

Blower speed regultaor (voltage regulator) on the vehicle is a very common, I would even say most common, fault in the climate control system.
It is a relatively easy repair as long as you have basic auto knowledge and experience - If I remember right those regulators are freaking expensive. Over 200 bucks.

Do you know where on the vehicle it is & how to test it?Thanks

It's been a while.

It's under the wiper assembly with the blower motor. I don't know the resistance spec sorry. Search on this site for DIY manual -it's such a common repair there should be one.

Before looking to the blower motor , I would check the 3 prong plug coming through the firewall by the booster
This is power and regulator trigger voltage from the Control panel to vary the speeds . The red and blk are 12v. but the yellow should go from 2 to 7 volts for the trigger voltage to the regulator... if you do not have this , your problem is not the blower or regulator, but rather the control variable voltage feed to the regulator[ variable trigger voltage...]

Thanks arthur.Tomorrow ill check that.When should I get my 2-7 volts at the yellow wire?Is it when I change fan speeds?Also I am guessing I should have it plugged in when I test it??Why do they use a "trigger voltage along with a voltage reg.Just wondering,.Thanks again.

<<Why do they use a "trigger voltage along with a voltage reg.Just wondering,.Thanks again.
<>>
A voltage reg is a trasistor that conducts power when a trigger voltage is fed to its gate .. vary the gate voltage and you change the output of the regulator, which is a switched ground for the blower..
You can also take the whole thing apart and ground the blue wire at the blower [ thereby eliminating the regulator from the circuit ] and that will put the fan into high speed ... but why do all that before you even know if there is trigger volts getting down to that mess [ I'm Lazy]

... kinda like pulling your starter out before you check the Nuetral Saftey Switch cuz your car won't turn over ..

I love that one " Hey man, it must be da starter .. my Uncle had dat trouble one time. yup,,"

Today at work I found that 3 wire plug near the booster.The black wire has continuity to ground,The red wire has batt voltage & the yellow wire has 1.98v on low speed & when the high speed button is pressed it has9.82v.I would think now I have a blower motor resistor gone bad but in my experience on other makes of vehicles when the resistor goes south you have one speed only,high.When you try low the blower stops & you have no blower at all.Maybe its a MB thing.What do you think?Thanks.

<<I would think now I have a blower motor resistor gone bad but in my experience on other makes of vehicles when the resistor goes south you have one speed only,high.When you try low the blower stops & you have no blower >>

OK , one more try.

You have NO resistor, you have a VOLTAGE REGULATOR...

So, you now know you have the proper trigger voltage from the controls for the REGULATOR .
Now you have to get down to the blower/reg and ground the blue wire at the blower. That jumpers the reg. out of the circuit and gives full bat. volts to the blower . [ remember I mentioned the reg is a switched ground ??]. If the blower now has HIGH speed , replace the regulator.. if not , then your blower has bad brushes or bound bearings, not allowing it to get to full rpm, in which case it needs to be fixed or replaced....

Thanks for all your help.Tomorrow Ill get at that blower motor.I replaced i about a month ago so I know how to get at it.And also,sorry about constantly calling it a resistor.I was a Chrysler/eep tech for about 10 yrs & now I have the fun of being a certified Audi tech.Gotta love those germans.
Ill let you know tomorrow how I make out.Thanks see-yaa

Well the verdict is in guys.......................
I grounded the blue wire & what do ya know..the blower motor took off full blast.I took the torx screws off of the VOLTAGE REGULATOR - not resistor & there not even really connected.They just sit flat against the regulator.Must be MB magic.I want to thank you for helping me thru this.I couldent have done it.Thanks again.

I was looking at prices on fastlane & I see there is 2 regulators approx 40.00 difference.One says Behr & one says Germany.Will they both do the job?Why is one cheaper??Has everyone had a good experience with fastlane?

Prob nothing wrong with the cheaper one. But, note the 'sitting flat' part. The device likely needs to be heat-sinked carefully to avoid blowing out quickly. Make sure mating surfaces are clean and contact is uniform. If heat-transfer compound is provided, use it.

Steve

Well the end of the story is I found a new regulator for $230.00.It came with the wiring attached so I didnt need to heat sync it.I installed it & now it works like it should.Thanks for all your help.
THE-END

I'm still confused as to where the blower regulator is, exactly.
Do I go in under the hood or behind the console?
Should I see the aluminum porcupine/heat sinks from under the hood?
I have virtually no fan right now, but I know the AC is working because I can feel cold air drifting out of the vents when the windows are down at 50+ mph.
I'm not a mechanic, but having just replaced my center muffler on the 91 300TE, I feel lucky right now :)