Garage => Mechanicals => Topic started by: jbrasile on 11 December 2011, 06:46 PM

Title: ACC - Believed to be finally fully and correctly functioning!!!
Post by: jbrasile on 11 December 2011, 06:46 PM
Ok Guys,

I think I have my car's ACC finally working 100%!!!

A couple of weeks ago I decided to bite the bullet and replace the vacuum pods in the top center of the dash, I had blocked  their vacuum lines and locked the defrost and center vent actuator in their open positions so I could get a decent working a/c system.

The job is not easy but after some creative thinking I was able to replace the "guts" of the defrost actuator which was actually the only leaky part. It is IMPOSSIBLE to remove the actuators from their mounting points because the pressure washers that hold them in place are super tight and ifyou force them you may will crack/break the top of the a/c box and then the project would become a real nightmare.

To access the pods:

1) remove glove box - drop the light and pry out the pressure clips that hold the liner in place, carefully work the liner out

2) remove center vents - move them upward and you will see a spring metal tab at each end, bend them towards the center of the car and voila, vents out

3) remove center vent surround - undo the 2 philips screws that hold the frame in place - BE CAREFUL NOT TO DROP THEM BEHIND THE DASH - disconnect the dash sensor hose and carefully pull its plastic attachment from the sensor, it is held in place using serrated tabs that clamp to the bottom of the sensor. Disconnect the sensor cable from its plug near the ac/ amp, withdraw the sensor from the top of the dash complete with cable, etc... Through the glove box and center dash openings carefully detach the rubber boot that goes from the back of the center vent to the top of the a/c box. Carefully work the center vent frame out through the glove box opening

4) remove top nozzle from a/c box - disconnect the center vent actuator arm from the nozzle flap. The nozzle is held in place by four pressure clips, two at the back and two small ones on the sides, once the side ones are removed they are impossible to re-install but that is not a problem since the the rear ones + the rubber boot from the center vents keep everything in place and air leak free. The rear clips slide out, again BE CAREFUL NOT TO DROP THEM

Now you should be able to see the pods, defrost is on the left vertically installed,  center vent on the right horizintal. Vacuum lines feed the defrost at the top and front (if your car has version II of the ACC starting in 9/78), and center vent connection is in the back.

In my case only the 2nd stage of the defrost pod was leaking. I was able to break the tabs that hold the top of the pod to the base and remove the rubber diaphragms complete with their arm. The idea was to replace the whole top and internals with parts form the new pod BUT the new top portion does not have a tiny grove at the bottom of the barrel so after hours  fiddling with it I just transferred the new internals to the old pod top and was able to firmly re-attach it to its original base even with the broken tabs. This operation requires the use of a vacuum pump to apply pressure to the new actuator so the internal diaphragms position themselves in such a way that you can close the little barrel.

Everything was looking great  but as I was putting the car back together the dash sensor cable got caught by the glove box lid stop arm and broke.... those things are soldered and go through a plastic cap so I was able to cut the wires, crimp new bullet female connectors and connect them to the original sensor stubs, it worked out perfectly. Tip: tie the dash sensor harness to the vertical part of the sensor hose so it stays away from the moving glove box stop arm.

I took a long trip with the car a couple of days after doing the repair and while the ACC was working a lot better than before it was still not perfect. Temps and air flow varied nicely and I no longer had the over compensation issue that had plagued the system for quite some time but I felt there was still room for improvement.

I had previously calibrated the temp wheel as per the manual with 900ohms at 75F but it felt like that was making the system dial in too warm at 75. Today I decided to recheck my calibration and found out I was  about 20-25ohms off when the wheel was at a dead center 75F, readjusted that and decided to also reconnect the fresh air flap actuator and pod that had been disconnected a long time ago in hopes of increasing a/c efficiency, they both checked out ok for leaks so I re-attached the corresponding vacuum lines and boy what a difference!!! System seems to be behaving perfectly now holding temps, varying fan speeds, closing and opening flaps correctly, etc...

All in all it has been a very satisfying project and tomorrow we will check system performance in real traffic conditions.

Sorry I have no pictures but I worked on the pod repair for 3 nights 3-4 hours each and had to do it  quickly because there was trip coming up to attend a wedding 300 miles away  and the car had to be finished.

Little by little I have grown fond of the infamous Auto Temp II we have in our 116's and now that my acc seems to be working as it should I think perhaps the manual conversion project will have to wait a few more years...

After working with the ACC for a while my advice to anyone trying to sort out their system is to be extremely methodical, patient and most importantly: do not be creative, fix/repair/adjust everything as per the factory. Plugging lines, locking actuators and playing with the servo/amp/dash controls will NEVER make your ACC work correctly and when it does you will marvel at what Chrysler / MB engineers accomplished over 40 years ago using vacuum, water and transistors...

Hope this post helps those trying to conquer our elusive ACC....


Title: Re: ACC - Believed to be finally fully and correctly functioning!!!
Post by: JasonP on 11 December 2011, 07:47 PM

Good job!   :)

I'll be using your post later when I tackle my own.

Title: Re: ACC - Believed to be finally fully and correctly functioning!!!
Post by: 1980sdga on 12 December 2011, 12:48 PM
Good save on the dash sensor Joe! Plus it's good to know that this job isn't a dash-puller  8)

Mine has been working 100% since the weather started getting cool and I'm really enjoying it. I usually spend a couple of hours behind the wheel at a time and the system really works well. Wide open when I start off on a freezing morning and then it slowly throttles back to a warm breeze as the cabin heats up  8)

I think that the fresh air flap is a lot more important than most folks think. It's seems counter intuitive but it does need to be operating if either the AC or heat is going to behave  ;D

Congrats on a job well done!`
Title: Re: ACC - Believed to be finally fully and correctly functioning!!!
Post by: jbrasile on 12 December 2011, 01:09 PM
Tks Jon!

Drove the car all afternoon with 90F outside. Well... temp control still a little iffy, it seemed to be perfect inside my garage yesterday but with the sun hitting the sensor I expected the system to react quicker and blow more air, cooler and longer. It will react very quickly to an increase in the temp wheel, lowering the fan speed and changing air flow but if you go from hotter to cooler it is sluggish, making the interior uncomfortably warm. I am replacing the amp with a new one I bought NOS a couple of years ago and will report back. Will also double check the servo pot is calibrated correctly.

Last night I remembered I bought a pod popper from George Murphy many years ago! So there was no need to break the female tabs on top of the defrost actuator pod, at least if I have to re-do it I can use the tool and make live a lot easier!

Glad to hear your system is working well. It's funny, ACC seems to work a lot smoother during the winter season, keeping interior temps just right...


Title: Re: ACC - Believed to be finally fully and correctly functioning!!!
Post by: jbrasile on 12 December 2011, 02:17 PM

Just came up from the garage, amplifier replaced with one manufactured in 2004 that I purchased together with the aluminum servo back in 2008. Looks like sluggishness is gone, system reacts a lot quicker to changes in the temp wheel. Also measured voltage on pins 1 and 7 at the amp connector without unplugging it and as you turn the temp wheel I could see between 5.5 and 6.5 volts as the servo "homed in" to the desired setting, those are the right values as per the manual, with the previous amp I was only getting 3.5-4 volts so there is no question that there was an amp issue at work.

More driving planned for tomorrow, very curious to see how if behaves under the sun in hot weather and heavy traffic.


Title: Re: ACC - Believed to be finally fully and correctly functioning!!!
Post by: 1980sdga on 12 December 2011, 03:12 PM
Good work on troubleshooting the amp!  Was this the Mexican amp that had the low voltage?

It does seem as if the system would tend to lean towards cold with the sniffer on the dash...
Title: Re: ACC - Believed to be finally fully and correctly functioning!!!
Post by: jbrasile on 12 December 2011, 04:50 PM
Yes, it was installed when I bought the car back in 2007 but I had replaced it  with a brand new unit together with the aluminum servo. Since I started detecting the "over control" issues I put the Mexican amp back but now that everything is connected correctly and I learned how to test all the components in the system  there is no question the old amp is not 100%.


Title: Re: ACC - Believed to be finally fully and correctly functioning!!!
Post by: jbrasile on 13 December 2011, 04:56 PM
A little update,

Drove the car today again in 90-95 deg weather and while system reaction times were correct, I felt that leaving the outside air flap operating at 80/20/100% automatically is not the way to go. Sao Paulo is a very smoggy city with one of the worst traffic in the world so exhaust fumes and other unpleasant smells will enter the cabin if the flap is hooked up as per the factory. I also think having hot air entering the air box reduced system efficiency and when the flap opened to 100% outside air the amount of air coming out of the vents is noticeably reduced. I have decided to disconnect the flap as before an plug the vacuum lines. Drove the car this evening, set the wheel at 75 and control and temps were just perfect, whereas before 75 would result in too warm of an environment now it is just right. Let's see what happens tomorrow during the day in the sun.