Topic: Altering ACC

[1980sdga]

I guess the biggest sore spot on these marvelous machines is the ACC system that is so prevalent on the poor SD's. I've read that MB bought the system from Chrysler ( Who abandoned it for being unreliable  ) and believed that they could cure it with some German Mojo.

Not sure how true it is but I remember seeing some 70's Dodges with a similar "wheel" control when I was younger.

Anyway...

I'm considering using the ACC panel to control a more conventional heat/AC system with just:

2 or 3 blower speeds - Maybe re-tool the "wheel" to control speed with either a pot or resistors. There's enough room between the wheel and pushbutton assy. to rig something up. There's even some metal there for mounting.

Heat - Water on to heater core.

AC - Compressor on, water to heater core off. Use the "AIR COND" button for compressor.

Defrost.

Dash vents.

Floor/ defrost.

I'm assuming the pushbuttons switch both vacuum and electric circuits so I was thinking about re-assigning them to control the flappers in the ducts and using one to control a vacuum operated in-line heater valve. Maybe use the little water pump if needed.

Any input on this?  I wouldn't attempt to re-label controls, I'd just have to know how it worked

Any input on this?  I've dug pretty deep into the car and still need to isolate the different flappers and the functions of each.

I guess I really need a vacuum pump to figure out the different circuits. A lot will depend on what's normally open and normally closed. I do know that all US cars must default to "defrost" so that's a start.

[Papalangi]

For the best diagrams check out unwiredtools.com  They've already done all of the hard work and will sell you a kit that leaves it looking stock but works like it should.

If your servo does not leak, you could expand on my idea and make it semi-auto.  I plan on using a RC servo to modulate a late model Ford (or the like) heater control valve.  The servo will be driven by the dial, max temp on the dial will drive the servo and the valve to full open and vice versa.  Since my ACCII servo leaks and I might have trashed it taking it apart, I'll just leave it where it is for now.  If you were to replace the ACCII servo motor with a RC servo, you could keep the vacuum switching intact.  Mines stuck on air out the side vents and defrost vent and I don't care that much about heat on the floor, I'll take the easy way out and just control water flow.

Michael

[1980sdga]

Thanks for the unwiredtools link! Lots of info there! It would be neat to get it working properly but I really have no desire to have computers running my AC again 

My servo was leaking from several cracks in it so I just bypassed it for now and my vents are stuck in the defrost position.



I'm guessing that these vacuum controllers switch the flaps?  They look like solenoids that just turn the vacuum off/on or reroute the path so it shouldn't be that difficult to get something working. If the pods that control the flaps are OK that is...

I'd like to know how the AC evaporator/heater core arraignment is set up.

[Papalangi]

Here is a link to the library pages for the ACCII system.

http://handbook.w116.org/climate_73_4l.htm

It's been awhile since I paid much attention to the vacuum portion of the system, I just use the buttons to control the fan speed and a ball valve to control the temp.

Here is a link to the Chrysler Auto-Temp system,

http://www.imperialclub.com/Repair/Lit/Master/281/cover.htm

Michael

[Tony66_au]

Its worth noting that if you bypass the thermostat your AC will be on as long as the AC is on, although this gives you cold cold air it also may freeze up your AC which buggers your fan and can cause it to spit shaved ice thru the vents.

And when you park the car it will defrost like a freezer which may dump water in your front footwell.

Tony

[Papalangi]

With the ACCII system, the AC is always on unless manually turned off.  The system varies the amount of heat to control cabin temp.  There is a provision to prevent freezing, I don't remember how it works right now but it's independent of the setting of the temp dial or position of the ACCII servo.

It's all a moot point for my car since the Freon leaked out an hour before I bought the car and I've not bothered to fix it.  Seattle weather doesn't require AC often enough to make me want to spend the money and time.

Michael

[1980sdga]

Wow, I'm guessing that the evaporator and heater core are stacked or something and share a plenum?

[WGB]

Does this system suffer from any  foam hinge flap problems that the HVAC system is afflicted with?

Bill

[Papalangi]

>Wow, I'm guessing that the evaporator and heater core are stacked or something and share a plenum?

I assume so, I've not had it apart that far.

http://handbook.w116.org/Climate/83-600.pdf explains how it works, including which flaps do what and when.

>Does this system suffer from any  foam hinge flap problems that the HVAC system is afflicted with?

I assume so, I think that the flaps are of the same basic type, just way more complicated than they needed to be.  Even when off, I have a fresh air leak from a vent on the right hand kick panel that makes it miserable for passengers when it's cold out.

To keep the evaporator from freezing, there is an evaporator temp switch that shuts the compressor off if it drops below 36F.

Michael

[WGB]

Thanks Michael.

Bill

[1980sdga]

Thanks for the input!  I've been working out of town lately but I picked up a Mighty-Vac today. Pretty sure it's an often used weapon in the MB arsenal 

I plan on hooking it up to the various lines and hunt down some flapper functions.

I'm assuming the "Foam Flap" problem is referring to material around the flaps to aid with sealing?  Does it get in the way when old or does it just stop sealing?

Sort of on topic... I'm guessing that the first diagnostic should be of the vacuum reservoir under the back deck and go from there?   

[TJ 450]

Not only does the foam aid sealing, it also locates the flaps and forms a hinge on some of them. The foam simply degenerates over time to the point where the flaps move about as they please. This is where they like to jam and never move again.

That is, until the unit is given an overhaul.

Tim

[Papalangi]

>I've been working out of town lately but I picked up a Mighty-Vac today. Pretty sure it's an often used weapon in the MB arsenal

A Mityvac is a very handy tool indeed.  It will take many a squeeze to work some actuators and there are some calibrated leaks so don't condemn something until you've isolated it best you can.  I'm kinda lazy so I used a vacuum venturi to trouble shoot my door locks.  My poor compressor ran a long time and didn't seem to be worse for the experience but goodness it was noisy!


>Sort of on topic... I'm guessing that the first diagnostic should be of the vacuum reservoir under the back deck and go from there?

The reservoir under the back deck is for the door lock system.  The ACCII reservoir is inside the left hand front fender and I don't think you can see it with out removing the fender.

Michael

[koan]

Takes a long time to pump down the A/C vacuum reservoir with a hand pump.

Takes an eternity to pimp down the door lock vacuum reservoir with a hand pump.

When using the pump don't try to evacuate down to zero, just go to typical engine vacuum levels.

Keep fluids out of the pump, I accidentally sucked up petrol and the seals failed shortly afterwards.

koan

[1980sdga]

Pimp down bro. pimp down with yo bad self 

I've actually had a cold for the past few days and have just been lying around. I know that if I get to fooling with it I'll tinker with it tooo long...