ACC Amplifier

[koan]

the problem happens no matter what temp you select but I noticed that on cold days the system works a lot smoother which tells me that the overshooting is being caused by the center vent being open all the time and preventing cold enough to the sides when max cooling is not required.

OK but still don't see why the system goes haywire when it's almost reached the set temp.

What do you know about the water valve / servo position? I suggested they might need to be synced up but can't see anything on it in the book.

koan

[jbrasile]

That is exactly it, once it reaches  the selected temp under the conditions in my example the center vent is supposed to close and cold air will be sent to the side vents. Since my center vent is locked open, the side vents end up producing warmer air and heating up the interior, in turn the system senses the increased temp and goes back to full cooling.

The water valve is part of the servo, and I understand what you are saying about get it synced, however there is no way to do it without dismantling the whole thing, and in fact I think the relationship between the electric motor and the valve is fixed, meaning you can only put the servo together one way when you rebuild it.

Tks for all your interest!

Joe

[1980sdga]

Wow Koan, your insights are awesome considering you've never seen the system in person!

You can kind of understand the gear/servo system if you look at it like a clock. The water valve is like the second hand, the electric switch wiper is like the minute hand and the vacuum switch is the hour hand. The servo motor can drive the mechanism a fixed distance in either direction but the relationships between the servo "sub systems" (water, blower speed and vacuum switch) are fixed.



Here's the sensor chain test procedure:

The electrical connection pins are numbered 1 to 10 from left to right looking at the "connection" side of the servo.

1  Connect ohm meter set at 2000 ohms to pins 1 and 2 (Feedback Pot). Meter should read 1400 ohms +/- 50 if the servo was in PARK            when disconnected.

2  Connect 12 volts positive to pin 4, negative to pin 5. The servo should run smoothly to the HOT pisition. The resistance of the feedback pot should decrease slowly and stop between 200 and 300 ohms.

3  Reverse power. Connect 12 volts positive to pin 5, negative to pin 4. The servo should run smoothly to the COLD position. The resistance of the feedback pot should increase slowly and stop between 1800 and 2100 ohms.

4  If all is OK connect 12 volt positive to pin 3 negative to pin 5. Servo should move partway toward HOT and stop in the PARK position. At this point the feedback pot resistance should read 1400 ohms +/- 50.

5  If the servo appears to operate properly and the feedback pot has no "open spots", servo is probably OK.  If the feedback pot does not read 1400 ohms +/- 50 at PARK from COLD loosen the pot retaining screws and adjust the pot position to read 1400 ohms +/- 50 at PARK coming from COLD.

At no time should the feedback pot resistance read "infinity", open, or drift up or down. If it does the feedback pot is dirty and needs to be cleaned.

6  Repeat steps 2,3 and 4 above until the feedback pot resistance always reads 1400 ohms +/- 50 when it stops in the PARK position.
COMING FROM THE COLD POSITION (1800-2000 ohms.

SENSOR CHAIN CHECKOUT:

Ambient Air Sensor- Should measure between 200 and 400 ohms depending on temp. (170 ohms at 104 F.  415 ohms at 64 F)  This can be checked at the MALE pins 2 and 3 at the test connector.

In-Car Temperature Sensor- Should measure between 1000 ohms and 2300 ohms depending on temp. (700 ohms at 105 F. 2500 ohms at 64 F.) This can be checked at the MALE pins 4 and 5 at the test connector.

Check of thumbwheel control-

1 It should read 900 ohms with the wheel on "75". If not insert a thin pointed knife blade along the RIGHT SIDE of the wheel. A light is handy for seeing the gears.

2 Position the pot at 900 ohms and hold it with the knife while rotating the wheel to center "75". The wheel should be centered at "75" with the pot at 900 ohms.  Make sure there is no play between the wheel and the potentiometer gear. If so dissasemble the panel and tighten the wheel-pot shaft.

I'm working on getting someone to scan the original document and post it as a PDF.

Is this the procedure you used Joe?  Make sure you keep notes when you change out the center vent elements 

[jbrasile]

Yes Jon, that is exactly what I did and evrything was within spec. I had to calibrate the temp wheel to read 900ohms at 75F and the servo pot was maybe 100ohms off so I adjusted that as well.

I am very anxious to get the new pods and give it a try, I will document it with pictures, including my modifiied hands, fingers, arms, etc.... hehehe....

Tks,

Joe

[1980sdga]

I am very anxious to get the new pods and give it a try, I will document it with pictures, including my modifiied hands, fingers, arms, etc.... hehehe....

Tks,

Joe

Maybe it won't be that bad.  I think it could be done by removing the center console and using child labor  Tiny hands you know...

Here ya go Koan:

http://forum.w116.org/mechanicals/is-there-a-simple-way-to-make-my-acc-always-blow-hot/15/

You need to figure this out 

[koan]

Here ya go Koan:

http://forum.w116.org/mechanicals/is-there-a-simple-way-to-make-my-acc-always-blow-hot/15/

You need to figure this out 

I've read the thread and am a bit lost as to what you are up to, thought you were trying to fix your system.

That is exactly it, once it reaches  the selected temp under the conditions in my example the center vent is supposed to close and cold air will be sent to the side vents. Since my center vent is locked open, the side vents end up producing warmer air and heating up the interior, in turn the system senses the increased temp and goes back to full cooling.

I'll have another look at the diagrams, I must have missed the bit on the centre vent closing.

koan

[1980sdga]

Sorry for the confusion. I'm going to send my servo off for a proper rebuild by an expert but I was tinkering with some alternatives in the meantime.

In certain heating positions the center vent closes and bleeds air to the "leg flaps".  All automatically