Does anyone have a successful Unwired Tools ACC installation?

Started by Rolo, 19 June 2024, 12:16 PM


Hi all, I told my mechanic that without this forum and their shop, I would have sold my car years ago.

I'm dissatified with the UWT ACC since installing last summer.  It has cost a bunch in shop labor to get the thing to work in its current state. I'm concluding the unit is not as advertised: Works just like the factory unit.  UWT Support has confirmed that there are now only 3 fan speeds in each Auto mode instead of 4 and the blower starts in heating mode even with cold coolant.

So what else is not just like the factory unit?  We've run all the diagnostics in their documentation, and it passes all tests.  But the following seem abnormal:

-Center dash vents in cooling mode.  They do not open immediately with very high cabin temperatures and cool ambient temps around 70 and lower.  Very cold air comes from the side vents, but the center vents remain closed.  Sometimes they open after several minutes, sometimes the trip is over before they open.

-Sticks in cooling mode long after cabin is cold.  The center vents (when they open) close, but very cold air continues to flow through the side vents.  We haven't had many cold mornings so can't say if this sticking occurs in heating mode, too. Increasing to 80 does slow the fan speed, but not for long. It jumps back to full cooling through the side vents.

-Only 2 fan speeds in each of the modes, Auto Hi and Auto Lo.

-"Hunting" fan speeds and heat/cool modes.  Unit will sometimes change fan speeds back and forth every few seconds.  Heat comes on and goes off with a cold temperature setting for a few seconds.  Cooling comes on for 3 or 4 seconds in heating mode.  Does this randomly and several times.  UWT states this is to correct overshoot.  Factory unit's solution is much more what you would expect.  Just shut off heat or cool as needed, not jump to a differnt mode.

-Bi Level mode sometimes works, but mostly not.  Center vents stay closed and sometimes open after several minutes of running.  Sometimes not at all.  going from Defrost to Bi Level opens the center vents.

I understand UWT deals with many DIY installers and they have done a tremendous amount of work developing a unit retaining all of the factory sensors, connections, and controls.  They are proud of their product and should be. Only once have they hinted I may have a defective unit.  Perhaps one of you can confirm if what I'm experiencing is the new normal for my car.  I will add that my mechanic is partly to blame.  He recalibrated temperature wheel and 85 is is the new 70.

Thanks and good luck to anyone contemplating not rebuilding their old ACC controller.


I know you probably don't want to hear this but...I am a proponent of the original ACC system as it left the factory.

Don't get me wrong I still think it's horribly overcomplicated and quirky, but once the original system is sorted out it actually works quite well.

Just my 2c ;D
1977 450 SEL 6.9 - Astralsilber


Maybe just further to this, now that I have actually read your post in more detail...When you read the sections in the service manual, you will see very detailed and clear guidance for the ranges of resistance readings in the sensor chain.  For example the temp wheel has corresponding resistance values depending on where the temp is set of course, and so also with the ambient sensor, as well as the resistence readings in the servo itself and also the in cabin sensor.

All this to say that troubleshooting becomes harder now that your system is not "to spec" as per the service manual.  For starters I would set the temp wheel to read exact, as this forms part of the sensor chain of course and could be throwing off both what the system is seeing for total resistance as well as time to react to changes in input.

The temp wheel is pretty much impossible to adjust in situ, there is a special Benz tool (of course) to hold the potentiometer gear steady while you adjust the wheel to get the proper resistance reading at the corresponding temp setting.  Best to remove the panel completely and do the adjustment on the bench with a multimeter.

Further, there is a test port under the dash where you can hook up your multimeter to read resistance values.  This is a pain to do but really unless you know that each component in the sensor chain is reading proper resistance (range) then your system will never run right I'm afraid.
1977 450 SEL 6.9 - Astralsilber


Thank you for the helpful insight.  Unfortunately, the horse has left the barn on the temp wheel.  It is way off.

My question is actually whether the UWT unit's behavior that I describe is considered normal.

UWT is strongly suggesting that the unit is doing what it should.  It's the vent operation and the hunting that is irritating at best.  UWT has has communicated that some of the behavior I report is "not possible."

And if this is normal, I'm with you.  I yanking out the UWT unit and rebuilding my factory unit.


I'm hoping that someone else with the UWT system can chime in then.  It does seem odd that they (UWT) claim it should work "just like factory unit", as what you are describing does not sound 100% right to me.  The system does take a bit of time to adjust to "new input" I would say, for example if the cabin is cold and you want it hot (assuming the motor is sufficiently warmed up), it should move to full heating action within about 30 seconds or so, and then stay in full heat until the cabin is sufficently warmed up.  If it hunts back and forth and randomly goes from heating to cooling without any input changes then I would say something is amiss.
1977 450 SEL 6.9 - Astralsilber


Here is a very good doc that explains how the system should work, this may help you, or (hopefully not ;D ) confuse you more:

1977 450 SEL 6.9 - Astralsilber


Thanks.  UWT Support has already disclosed differences from OEM including running the heat mode when the coolant is cold.  What I'm trying to determine is whether the "sticking" and the "hunting" are normal.  I do know that the vents not opening is not normal, but UWT's response is that is not possible.

I did discover a hack.  By going into Def mode and then Auto Hi or Lo, the center vents do open.  That also stops the cooling mode.  Based on my limited hardware and software exerience, it looks like the controller is unable to enter Auto modes directly from system start up.  It needs to "launch" those modes from another mode first. The system runs on start up, but it does not at least appear to run correctly.  As mentioned above, center vents also don't work as expected in Bi Level, but do after first going to Defrost.


I'm of the same mindset as Daniel.  I prefer the original set up, so I can't comment on the UWT unit.  Though, I do have a few questions about that parts of the system that are still original. 

Are your vacuum actuator diaphragms ruptured or leaking? If they are, then the various flaps they control will intermittently work or not work at all. 

Does the UWT unit integrate into its operation the original amplifier?  If so, maybe that is stuffed.  If not, then it can be completely ruled out. 
1966 250se coupe`,black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3,papyrus white/dark red leather
1975 450se, pine green metallic/green leather
1973 300sel 4.5,silver blue metallic/blue leather
1979 450sel 516 red/bamboo


Not an UWT user, but used the Hamilton box which also proved to be unreliable. Had to get a unit RMA'ed and the replacement died after a year. They have also been super poor with communication, despite the supposed lifetime warranty.

Planning on driving cross country later this year and hoping to sort out the Climate Control before I leave. Kind of leaning towards going back with the servo/amplifier. That's a new headache though of getting an old servo (since I didn't keep mine) to exchange for an aluminum one. Not to mention hooking everything back up again.

Does anyone know if the ACC box sold by Mercedessource is the same as the UWT? The price is lower than UWT but looks pretty similar.
1979 300 SD "Liesel", 282k Miles


Quote from: UTn_boy on 19 June 2024, 08:14 PMI'm of the same mindset as Daniel.  I prefer the original set up, so I can't comment on the UWT unit.  Though, I do have a few questions about that parts of the system that are still original. 

Are your vacuum actuator diaphragms ruptured or leaking? If they are, then the various flaps they control will intermittently work or not work at all. 

Does the UWT unit integrate into its operation the original amplifier?  If so, maybe that is stuffed.  If not, then it can be completely ruled out. 

Thanks for the questions.

The flaps are working intermittantly, but I have ascertained that very briefly selecting Defrost, then Auto Hi or Lo always opens the center vents when the cabin is hot.  Now that its 90 out, I'm seeing the center vents opening more often.  Leads me to believe the system is weighting the ambient air temperature much more than cabin tempertures.  Why hitting Defrost first always opens the center vents in Auto Hi and Lo could be a hack I've discovered.

The oddity is that while the center vents remain closed, the side vent air is really cold.  So the ACC is telling parts of the system to get cold.  Fan speeds are high in both modes.

Last year while troubleshooting, UWT told me the cabin sensor tube to the dashboard was disconnected, so it's possible the cabin temperature sensor is bad, althought until the old ACC failed, all was working well.  My shop recalibrated the temp wheel last week so a set 85 is around a true 70 although selecting 65 doesn't open the center vents consistently. (I can't get much heat now)

Here's UWT documentation.  A lot to wade through,

In any case, you are all correct.  This replacement ACC was a huge mistake.  Wish one of our members with a working UWT would pick up on this thread. 


Sorry to respond to my own post, but below is what I have been able to determine from UWT documentation, trial and error, and a couple of emails from Support.  Thought this would help others looking at a UWT conversion and will close out this thread.

Normal operation which differs from factory:

Center vents do not open unless outside ambient temp is 8 degrees higher than what is selected on the temp wheel.  Cold air will come from side vents.  A sunbaked car on a 60 dgree day won't open the vents when temp is set to 70.  You can turn the temp down, and the ACC will open the center vents sometimes after a 10 minute delay.  This is not Automatic Climate Control, it's manual.

2 fan speeds with the lower speed higher than the factory lowest speed.  ACC starts at the higher of the 2 speeds most of the time and after 5 to 20 minutes will drop to the lower speed.  In cooling, you may also get a burst of heat to correct the "overshoot."  In heating mode, vice versa.  The ACC is very slow to respond which led me to belivve it wasn't working at all.

ACC switches on when coolant is cold.  You get cold air on start up.  You will need to shut the ACC off if too cold.  Manual climate control.

To conclude, the UWT ACC is not as advertised.  It does not operate the same as the factory unit.  What I was mistaking as a bad installation or defective ACC is the way the UWT unit was designed to work.  Not as adverstised.


Quote from: daantjie on 19 June 2024, 12:22 PMI know you probably don't want to hear this but...I am a proponent of the original ACC system as it left the factory.

Normally I'd prefer to work with the factory system, but what can you do with a servo unit that is completely corroded and seized internally?  Workable used servos don't seem to be available anymore, so a UWT unit or the even more expensive aluminum reman ones seem to be the only alternatives.
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)



You can find plastic bodied ones on ebay but finding one that's not cracked is of course a challenge.  Then of course you run the risk of it cracking on you after a while.  As with most things regular use is key to work the gearing and such.  Also correct antifreeze is key as well.  But agreed the aluminum bodied ones tend to hold up better long term.

You can always spring for a NOS one from this Saudi outfit, for a mere $1300 USD...
1977 450 SEL 6.9 - Astralsilber