What I learned about 74-78 ATC II

[73 T&C]

I love this thread. But most of all, tell us where to go to get the darn thing fixed if it breaks!

Read on.

 

[cantflip]

I love this thread. But most of all, tell us where to go to get the darn thing fixed if it breaks!

DIY or mail the car to Miami... , your local shop will most likely want easier work.

 

[73 T&C]

Part 2.

The components that make up the ATC II
More than the sum of its parts



Those of you familiar with my other thread know I’m refurbishing a 78 NYB. It came to me in very good overall condition needing only some delayed maintenance to get her up and running decently.

She also came with the storied ATC II. And it was inop.

This section will show the what and where I checked and what I did to get the ATC II up and running again.

For illustration of the parts that I would check I’ll be using both the FSM (Factory Service Manual) and pictures of the actual parts.

But first, a brief word about the need for the specific FSM for the car you’re working on.

The word: Before

Get one, read it and do your best to understand it. BEFORE you start.

Read the descriptions, look at the diagnostic matrices in the back. In fact.... start with those.... it’s like reading the questions at the end of the chapter before you read the chapter. Believe me... when you finally read the chapter you will have one revelation after another.

So you say you don’t have an FSM? Well here it is:

 

[73 T&C]

Part 2

ATC II Section from 1978 FSM - Section 1

(We’re only allowed 10 pictures per post so this will take a few posts)

 

[73 T&C]

Part 2

ATC II Section from 1978 FSM - Section 2

(We’re only allowed 10 pictures per post so this will take a few posts)

 

[commando1]

Ahem, cough cough.... Please notice the Troubleshooting Chart above, people.

 

[73 T&C]

Part 2

ATC II Section from 1978 FSM - Section 3

(We’re only allowed 10 pictures per post so this will take a few posts)

 

[73 T&C]

Part 2

ATC II Section from 1978 FSM - Section 4

 

[73 T&C]

Ahem, cough cough.... Please notice the Troubleshooting Chart above, people.

View attachment 176617

Yep.... 8 pages of it!!!

 

[73 T&C]

Part 3 - The parts:

INPUT SENSORS and THERMOSTAT

Ok no excuses..... now you know what I know.

So let’s start with what I had to do: Finding the dang parts the book is talking about in the dang car.

Along the lines of my previous discussion, I’ll be starting with the input side.

Sensors;

In the previous part I talked about the two temperature sensors. Well the first was easy.

The cabin ambient temperature sensor is just to the right of ATC II control panel.

It’s the one with the snorkel coming off of it.

The outside ambient air temperature sensor was a little more challenging.

Here it is as shown in the FSM

And here it is in the car...,

What the FSM doesn’t tell you is that you have to take the right side dash speaker out just to pull the sensor out to test it. Once you find it that is. It’s also behind some insulation too.

You might be able to get it from the wiper well .... if you have 6’ long orangutan arms and eyeballs at the end of your fingers.

Luckily both of my sensors were good.

The thermostat comes next, but is actually first in the series.... literally they are wired in series.



(Picture of slide thermostat with ohmmeter readings high and low. )

Ok.. I’m sure you’ve seen this before but it’s worth mentioning that it comes out from the front rather easily. Connectors are right there and ready to check.

 

[73 T&C]

Part 3 - The parts:

THE SERVO


The FSM describes the unit as follows from the testing section....

And shows it like this.

The reality is more like this.

This a close up of the servo mounted on the air box. Note that it’s just to the left of the inside mounting bracket for the air box to the inside firewall bracket.

Here’s the actuator bar for the blend door from the servo. It uses a self adjusting spring clip like the old wire actuated Mopar heater valves. The little bar just beyond the servo holds the bar down on the servo. It looked like it may have had some grease on it.... 40+ years ago. It will have some fresh grease there when I do mine.

To help you understand the size of the servo, I took a photo with my average sized hand next to it.

The bend door actuator clip slides right up and off

This is the blend door crank arm.

You can’t see much of this when the air box is mounted in the car.

(Insert picture of box closer in and to the left)

This is a good picture from the FSM that is from the testing section but shows well the air box and servo. It’s right there next to the mounting bracket for the air box. It has all the surrounding trim and accessories removed. (Note that the complete lower dash section, kick panels and even door sills are pulled. Changing the evaporator or heater core will be a chore.)

 

[73 T&C]

Part 3 - The parts:

THE AMPLIFIER

Interestingly, this is the easiest part of the ATC II to get to.

To the extreme right side of the air box in the passenger foot well.....

Just to the left of the recirculating air vacuum motor......

you can find the amplifier

Here it is on the air box out of the car. It’s held in place with three nylon rivets. But you only have to remove the front two by the connector to remove it because.....

the third just clips into space on the back of the stock Mopar unit. Note that the reason for the nylon rivets seems to be the proximity to the end of the evaporator core on the other side.

This amplifier I was able to scavange off an Airbox I bought just for the purpose of taking it apart and as a possible source for misc parts.

I plugged it into my working system to test it and it worked perfectly. It cycled from A/C to heat no problem. These things do get warm when powered up. So I need to be sure to keep it tight to the cool part of the airbox. I now have a working spare. The extra ATC II air box purchase has just paid off!

Here’s the replacement one that got the system to work. It’s a VDO replacement from Germany. It’s actually interchangeable between the earlier 69-73 and 74-78 ATC II. Worked like a charm. Of possible interest, it only has two mounting holes and the grille is a little different. Otherwise, it is dimensionally the same.

Hmmmmm. Where have I seen this before....

Why..... in the FSM of course!

 

[commando1]

So is it out yet?

 

[73 T&C]

So is it out yet?

Still waiting for parts. Next week. Maybe. Patience my friend. Patience.

 

[commando1]

 

[73 T&C]

Part 3 - The parts:

The AIR BOX Part 1

I bought an extra air box in preparation for the replacement of my evaporator core and heater core. I wanted to salvage some spare parts (if they turned out to be good) as well as learn on a junk part how to take it apart and out better. I have done this often with great success and enough to become the bain of my local junk yards. The FSM is a little weak on the “how” and almost assumes you’ve done it before. And, if you’ve never done this before on this particular car or it’s corporate brethren, I’m sure you’ll find that the process is far from intuitive. What to take out, when, in what order and what to leave on is a big question.

The upshot is I learned a lot and was able to get some critical spares in the process.

I was also able to get some insight into the assembly of the car and process I will need to follow in the removal of the air box which I plan to document separately. This part is only about the air box, it’s dissassembly and critical steps to follow. Little here is described in the FSM as it relates to the ATC II.

A quick review of the photos I took tells me this section will be a multi post effort.

This is the overall view of the air box. It looks a lot more complicated than it is. By taking it apart, I learned it is a very well engineered assembly of components that accomplish a series of tasks in the processing of making conditioned air. And, for its size, is actually fairly compact.

After taking it apart, it’s really just a big two compartment plastic bucket with a screw on lid that holds all the components together in a particular way. Simple!

To the extreme left side corner is located the vacuum motor for the defrost vent. Although it’s not required to be removed to open the box to replace the evaporator or heater core, I will want to take it off to protect it when manouvering the airbox out of the car due to its exposed position. Two speed nuts and a spring clip similar to a large carburetor choke clip and two vacuum lines is all it takes. Word of caution..... you’ll want to mark all the vacuum and electrical lines you disconnect to save you time on the rebuild/install.

Located at the. Top and extending down the front of the air box is the servo unit. It is held by two 5/16 or 8mm hex head sheet metal screws. As I would discover soon enough, someone had been in here before me. Probably.....to change out the evaporator.

And here’s the evidence... two extra sheet metal screws and glue used on the right side of the servo to hold it in. Well out they all come. Likewise the previous section about the servo outlined the removal of the blend door arm. But.... let’s not yank on it just yet. I see where maybe we won’t have to disconnect anything to get the top of the box off.

Let’s start by loosening the vacuum switches for the master switch and compressor switch. Without disconnecting them, we can just remember be their mounting plate. And just below them is the main blower resistor with three very different plugs. It will be hard to mix those up. In order to remove the airbox from the car, I will have to disconnect only the recirculating/outside air vent vacuum motor and position switch connector, the two main harness connectors being the curved grey one and the square white one on this side of the airbox. On the other will be the jumper connector for the vacuum connector to the control panel and the aspiration for the cabin ambient temperature sensor.

Here is the main harness connectors mentioned above.

I found missing screws in holes at the top. Here’s one.....

.....and here’s the other. They line up with the evaporator below. Hmmmm... new evaporator? From what I’ve seen of the air box in the car, it is in much better shape than this salvage unit. As to whether or not this salvage unit has a replacement evaporator, we won’t know until we take apart the unit that’s in the car. I’m pretty sure that one is original. But.... Let’s hold this question for now until I get that original unit out of the car.

It was when I removed the servo that the lights went on.... you can remove the whole electro-vacuum harness for the ATC II leaving the vacuum motors connected. That was when I noticed that the only thing left holding it on was the connectors for the blower resistors.

Now, all I have to do is to remove the vacuum motor for the heater-A/C air direction damper and the blend door actuator ..... and the top should come off free.

(The bent tang on the support for the vacuum motor happened in shipping. The seller was kind enough to remove this motor and the defrost motor without disconnecting them for shipping.)

 

[73 T&C]

Part 3 - The parts:


The AIR BOX Part 2

The vacuum diagrams in the FSM show that there are two of these that can produce a variety of malfunctions if not connected properly. The ones in the car are working properly so it would be best not to disconnect them on the car as the reconnection later may be a nuisance.

The blower resistor is another part I need to test to keep as a possible spare.

The blend door actuator and bell crank and.....

the direction door bell crank are all that is remaining to remove the lid.

The lid for the air box is attached with these 1” sheet metal screws. The smaller ones attach the evaporator and heater cores from the outside of the air box to flanges/airseals built into them. All are 5/16” hex head.

You can see here that the whole electrical/vacuum harness is laying off to the left. And after I removed the blend door actuator and direction door bell crank, .....it’s up, up and....

Away!

The lid is insulated with a thin layer of appplied foam. This one still has that insulation well attatched.

In order to get the two cores out, there are several sets of screws attaching the cores to the box.

While we’re looking at the back, I can see clearly that there are only six bolts that attach the airbox through the firewall. Four of them go through the blow and manifold directly into the evaporator opening. The other two are about equidistant further inboard near the inlets for the two cores.

 

[78Brougham]

The wheels on the bus go round and round, round and round.

 

[73 T&C]

Part 3 - The parts:


The AIR BOX Part 3

With the lid off, you can easily see how the direction and blend doors work to move the air coming through the evaporator either through the heater core and down to through the heater outlets or directly out the front to the dash vents and spot coolers.

A look at the pocket for the blend door reveals where the two cores are screwed together. Again the use of the same 5/16” hex head screws add to the consistency.

Pulling the direction door straight up and out, gets you direct access to the screws.

There at two pairs of screws on either end of the box holding the cores in. The ones on the opposite side are aligned to just miss the evaporator core thrrefore removal and replacement will need to be done with care.

Heater core slips straight up and out

You can see where it’s been leaking slightly for a long time.

Same deal with the removal of the evaporator.
Up and out.

This is the back side of the coil. Unlike the heater core, this evaporator core looks pristine.

Both sides

And the coil manifold too. Now the only thing left to do is put in new core and follow these steps backward to completion.

 

[commando1]

Here's a manual HVAC box I took apart recently. Looks like they both use the same box.

BTW, I discovered that the vacuum actuators are GM and they repop them.