What I learned about 74-78 ATC II

DIAGNOSTIC cont. (3) revised and expanded

My A/C works well but never puts out really cold air. What is that all about?


The AutoTemp II is a chill/reheat system. This means that all the air being conditioned is first run through the evaporator and then none, all or a part of it is run through the heater core and directed either to the upper or lower vents. Unless the outside temp is less than about 40 degrees, and the system is set for anything but OFF or VENT, the compressor is running all the time in this system. Likewise, the heater valve will be full open.

If you think that the system is not making cold enough air, you may have one (or more) of the following issues:

(With the upper dash removed for access and, of course, assuming that the system is capable of making air cold through the evaporate down to between 35 and 45 degrees).....

1) One or more of the ambient temp sensors is off spec. Not very likely.... if you got this far. But, if you haven’t checked them up to now, check them all now in accordance with specs outlined in the FSM on page 24-118.

2) Blend door in the airbox is not set correctly at the servo. Adjustment of the link needs to be made so that, at the 65 degree setting on the control panel, the servo actuates the blend door to full open with no or very little blend air. (Typical for these systems after 40+ years)

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This is the link that needs to be adjusted. This link is described as “self adjusting” in that, once adjusted, it will self-locate the blend door to the full closed position against the heater core chamber whenever the servo moves to full cold.

To adjust, you need to shorten the distance between the end of the looped hard wire and the curled spring steel link. Thumb on the loop end and index and middle fingers on the spring clip ,(if your right handed and coming in from the right) and very gently squeeze the distance in between to about 1”. Don’t go crazy here.... like Brill Cream... “ a little dab’l do ya”
All systems are slightly different and after time, shinkage of the insulating foam on the blend door and the seals that help control the air through the air box may be allowing enough leakage to inadvertently warm the air that is being processed more than necessary.

3) The aspirator that draws the cabin air through the interior ambient temp sensor is not connected properly or is not drawing enough or any air. For example...

If it’s been a cool night and the sun has not warmed up the car but the outside temp (or just your own desire) has you set the system to 65 degree full cool but there is not enough warm air being pulled past the interior ambient air sensor to warm it, the system will misread the interior condition as already cool and throttle down its cooling capacity. Hence, the complaint that it’s not cooling enough.

Confirm that the aspirator “snorkel” hoses of the aspirator are properly and fully connected and that they are also clear. Blow out the hoses with some compressed air to clear away any accumulated debris that may be interfering with the airflow. (Someone trashing around in the tight confines of the area around the aspirator may have slipped off one of the connections which are only attached with friction.

One more thing to confirm is that the internal ambient sensor is actually receiving only cabin air.

These cars are now all past 40 years old and the distribution ductwork seals may not be doing a complete job.

If, for example, the seal to the center vents is not tight to the dash box, a leak of conditioned air near the sensor will throw the whole system off. Cold conditioned air will directly cool the air adjacent to the sensor intake more than the actual air temperature in the cabin resulting in a misread and false response by the system to throttle down the fan and increase the amount of blended warm air.

As much as the seals around the blend door being good, the seals around the central vents should also be checked to make sure they are containing the complete conditioned air stream.

I found that my seals around the main duct were leaking at the dash and a portion of cold air was being directed between the dash pad and the edge of the instrument panel near ambient air sensor. I just cut down some foam to pack and fill the gap until the next time I pull the dash pad to solve the immediate problem and remind me later to replace the seals around the main duct feeding the dash outlets.
 
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awesome thread with lots of info. This may be a dumb question but how do i know if i have ATCII i have 77 new yorker with AC that the ac has never worked since i bought it back in 2014. Finally have some time to start messing with it. Did all these high optioned cars come with this system back in the day? Thanks, Nick
 
awesome thread with lots of info. This may be a dumb question but how do i know if i have ATCII i have 77 new yorker with AC that the ac has never worked since i bought it back in 2014. Finally have some time to start messing with it. Did all these high optioned cars come with this system back in the day? Thanks, Nick
Dash Control says AutotempII. It was optional on NYB.
 
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Introduction

This is not my first attempt at repairing Automatic Temperature Control (ATC) systems. Having successfully beaten several Cadillac climate control systems into submission in the past, fear was not a determining factor in keeping me from digging in and trying to learn about and trying to bring back an ATC II.

In response to what was perhaps a casual suggestion, I thought it would be useful to both current and future members for me to create a specific record of my process in bringing the ATC II system in my 78 Chrysler New Yorker Brougham back into a functioning system.

Besides, after just getting mine to work, I will be taking it apart again to change out a leaky evaporator and possibly dodgy heater core in order to get my system back up and running reliably for the next few years....hopefully.

If your expecting this thread to be an extremely technical dissertation, it will not be. I’m thinking most people drawn here will just want to trouble shoot and repair their system. So that will be the focus, as it was mine at the time of this writing. After all, you don’t need to know the exact chemical composition of gun powder, the thermodynamic wonder of combustion or it’s exact burn rate to be able to effectively load, use or diagnose a problem with a firearm.

Likewise, if you want to learn about general manually controlled HVAC systems and their operation, repair etc. you need to come into this already knowing well how that works for this thread to be of use. After all, the ATC II, as the name implies, is about the automated control of both the heating and refrigerated air conditioning system.... so you don’t have to.

Before I began my repairs, and even before I actually had the car delivered, I began by doing research on this site, the web and factory service manuals that were relevant. Among the best information and source for needed parts was the Imperial club.

Online Imperial Club (OIC) for Imperial, Chrysler Imperial, and Chrysler New Yorker Brougham Enthusiasts

A fairly in depth description is available to anyone on this site which is a good way to start. In fact, I would read the article on the first version of the ATC II in the 69-73 earlier version of this system to understand not just it’s operation but the evolutionary advances made in the later 74-78 version to be described here. Likewise, for those so inclined, this specific article will greatly help you make sense of the actual Factory Service Manual description. It did for me.

What I will be describing over the next few postings will be: The basic operation of the system; Location and description of the components with pictures of both the parts and their location and; Finally, I will try to make a more useful trouble shooting guide to put down what I’ve learned in a useful series of checks and observations specific to the later version ATC II.

Because of the wealth of information in the enthusiastic community of owners, any and all relevant comments are welcome!
69 didn't have airtemp2 they had the early crappy airtemp1 which used a vacuum operated servo. The airtemp2 used a electric motor servo which controlled a mode switch for blower speed vacuum and temperature. It's a simple design (airtemp2) pre 1974. I rebuilt a few of them myself. The only really bad thing is the servo housing cracks and dumps antifreeze everywhere. Simple JB weld seems to fix them.
 
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