ATC II

[twostick]

Warning, looong post.

I'm in the process of trying to resurrect this system on my 71 Imperial. I know, good luck with that... The priority is to get the AC to function.

I'm assuming the servo box is seized/FUBAR because the temperature control doesn't function. All hot all the time no matter where you spin the dial to.

I have removed the hot water supply by looping the hoses ahead of the controller. No more hot air.

When I push the Hi Defrost, I get high fan and air to the windshield.

Hi Auto gets me the floor but no dash vents.

So I'm assuming the servo isn't selecting the right vacuum position to move the dash air door to position because it's stuck/parked.

In the process of finding where all the R12 vanished to, I discovered a bolt missing from the suction line on the back of the RV2. I also found a wire connector just laying there that I think is for the ETR valve that seems to be missing in action.

I replaced the 5/16 hex head bolts with socket head bolts because some retarded engineer thought using a hex head bolt that clears the fitting by .000001" was a good idea.

I pulled 30" vacuum on it for about an hour, closed the gauge manifold valve and it still held at 30" an hour later so I added some 12A R12 equivalent which I'm pretty sure is propane.

AC clutch engages without the ETR Valve present, so I put in 2 cans, which isn't enough to fill but enough that I'm getting cool air to the floor or the windshield depending on which button is pushed. Each can claims to be equivalent to 27 oz of R12. The tag says the system holds 4lbs and some ounces, either 6 or 8, the stamp is a little blurry, so probably safe to put in another can once I confirm system integrity.

Assuming I can get the servo apart and manually move the valve into dash air position, my concern is the missing ETR valve. What might blow up if it isn't there?

I can get an NOS one if it's critical that it be there.

Kevin

 

[Ross Wooldridge]

As far as I know, nothing will blow up, just that the evaporator may ICE up... the ETR as I understand it simply regulates the evaporator temperature to prevent icing, either by allowing just the littlest bit of coolant through the heater core to melt ice accumulation (done automatically with a special AC only Ranco valve on earlier non ATC AC systems), OR, shutting off the compressor and re-engaging it when the sensor deems it appropriate.

If it were me, I wouldn't worry about it.

However, I'm no expert, so I am interested what others here who are far more knowlegeable about these particular systems have to say.

Dash vents (also known as spot coolers) should only work on AC mode. Heat will give you the floor plus a tad of window, and Defrost will give you the window only.

With an ATC system, you may ONLY get dash spot coolers if the temp wheel is at or near the coldest temp setting. Not sure.

 

[Mr C]

Give this a watch...

Since you got the compressor cycling, you are where this fella is in the video:



On Fuselage ATC II Imperials the servo and amplifier are all combined in the under hood unit. In 1974 Chrysler "blew up" that design and moved the servo and amplifier inside the car and left the coolant regulator under the hood. Same system just moved the parts around, so it's an Autotemp II mark 2 from 74-78.

Anyway, your symptom of air not redirecting into the dash etc as commanded is an amplifier failure (the electrical connection part of the under hood box in the video.)

I had the same problem with my 77 Chrysler and I was able to fix it with a new amplifier.. the air goes where I command it now.

It was nice that I didn't have to replace everything, but just a component. A benefit of the mark 2 Autotemp II.

I have never seen a servo fail in 30 plus years of Autotemp II car experience. The servos are always incorrectly blamed in my experience. Servos need vacuum and electrical signals to operate. SO it's either a vacuum leak, or the electrical amplifier that is your problem. In my experience it has almost always been the amplifier (I did have a vacuum leak once).

 

[CBODY67]

As to the vent response from the switches, on a normal a/c system, when no vac from the switches is present, from the vac reservoir or its vac source, the "default mode" is air through the defrost and floor vents at the same time. Might be a leak from the source vac line or a leak elsewhere in the switching mechanisms.

Years ago, a friend was parting out a '70 or so NY. Where the EPR valve would go, there was a brass wire mesh item there, with an elec connection on it. Never yad seem anything like that, but later research indicated it was for an AT system. Never did understand why electricity needed to be there, or if it was just a "convenient" place for a ground>

Why is the compressor cycling on and off (by itself?)? When it should be running continuously?

There are a lot of threads in here about how to get the ATC II systems repaired. Is the "Search" function not working? Just curious.

The other thing is that the ATC II controller was used by Mercedes, so new/reman controllers can be had aftermarket.

In reading through some of the factory diagnostics, it seems the ATC II system is far too complicated for what it does, compared to the GM ATC systems. In hardware and complexity, but that is par for the course compared to GM, generally. Still, the system operates on vacuum supplied by the engine (via a switching mechanism and related vac servos) and electricity from the vehicle's charging system (modulated by on-off switches and variable resistors/potentiometers).

Just some thoughts and observations,
CBODY67

 

[MONC440]

The MyMopar YouTube channel has a bunch of A/C Master Tech videos. I watched some of them before converting my ATC to manual A/C

MyMopar. com