What I learned about 74-78 ATC II
- Thread starter 73 T&C
- Start date
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)
View attachment 181327
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.
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)
View attachment 181327
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.
Last edited:
commando1
Old Man with a Hat
Didn't we discuss this already?
commando1
Old Man with a Hat
Bullshit. You were going for a second opinionAlzheimer's sorry.....
commando1
Old Man with a Hat
There hasn't been a car salesman that's got the best of me.
Can’t fool you can I???
Yet....
commando1
Old Man with a Hat
Salesman had nothing to do with it.
It was the drugs.
75 Olds Starfire. This is your brain on drugs.
Any questions?
Hey, it was 1975.
77NyKR
New Member
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.
Manual A/C has a fan speed switch on the right side of the controls.
ATC II does not have a fan speed switch.
77NyKR
New Member
Thank you I do not have ATCII i have the fan speed switch
commando1
Old Man with a Hat
Whew....
DocGonzo
New Member
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.
Bob with one O
New Member
Anyone have the ATC Tester C-4144 or C-4315 for sale??
3175375
Senior Member
I just discovered this thread and it’s really good. Great work!
I will read this in depth and provide some feedback for consideration.
I will read this in depth and provide some feedback for consideration.
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