Chrysler Repair: climate system on maximum defrost--controls do not respond, climate system, intermittent basis

Question
Roland;

For some unidetified reason (lower humidity?) my comfort controls have begun responding on an intermittent basis. The single constant code I receive is 36 (degrees F) when I follow your directions.  I have done this five times and I have queried the system for additional problem codes and it offers none.  What does 36 mean and what's my next step?  

Thanks again.  You are th only person who has offered me real, concrete, steps to resolving my Chrysler AC problems. And I've asked a lot of local automotive professionals.

Thom

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Followup To
Question -
First, thank you. Now the rest of the news.
Within five minutes of my sending you my question yesterday I jumped in my car in the midst of a torrential summer downpour and the AC system returned to normal with ignition.  This was the first time in over two weeks. I note the presence of the rain and the cooling temp becuase it appears to me to be related in some key way to my AC problem. My defrost has been stuck on max since a 88- 90 degree heat wave began before the holiday weekend.  Before that it seemed flop back and forth from controlled to uncontrolled in some weird connection with the temp and humidity.  Since I had not read your e-mail yet, I failed to try to run the diagnotstic test.  This morning the temp is climbing back into the 80s, there is no rain and the defrost is pumping away no matter what I attempt.  I suspect that means the fuses are okay. I will check the wires. I just thought that this information might help pinpoint the problem.  I appreciate your help.  

Thom
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Followup To
Question -
My 1994 LHS is stuck on maximum output defrost and will not respond to any commands from the controls.  Display lights do not appear on the climate controls in this situation.  Nothing works on the AC or heating system except all-out defrost all the time. It started by running this way for a short while (15-30 min) upon ignition. then it would stop putting out hot defrost air and the temperature display lights would return and the system would once again respond to controls. Now it appears stuck in the permanent defrost mode.  Temp in the car must approach 120 degrees.
Answer -
Hi Thom,
The ATC unit has some ability to self-diagnose its problems but to take advantage of it the diplay has to be lit because fault codes are presented on the display for such diagnostic information. I would suggest that you look at the fuses in the junction box, under the dash (driver's side) and see if you can find ones that are assigned to the A/C or heater system and inspect them to find any that are blown, looking carefully at the interior conductive wire of the fuse for a minute crack that caused the fuse to fail (rather than frankly blowing a big gap in the wire). Replace any that are defective. Similarly, look at the fuses in the power distribution center under the hood (rectangular box on the driver's side) to see if any of those are similarly damaged, and replace if so.
Once you get the display back: On the ATC console there is a self-diagnostic capability that you can get to give you a code number as to what is wrong. Just set the unit for 75F, idle the engine, and then simultaneously press the floor, mix and defrost buttons (which are the first, second and fourth on the top row) and hold them until the display blinks, then release the buttons. The control display will then show a two-digit number if it has caught a problem. Then press the Panel button (first button on the second row) to see if any more codes come out. When the panel button push results in the display returning to 75 all the codes have been displayed. Either write back with the codes number or go to www. allpar.com/fix/codes_climate.html for a list of code translations.
Roland
Answer -
Hi Thom,
That intermittancy is interesting. It may be just a loose electrical connection, or one of the two temp sensors that control the unit is flakey. Perhaps it is the ambient temp sensor that I believe is located along the air intake to the heater/AC unit. But try to get the trouble code readout when the unit is working to verify if that is the case or not.
Roland

Answer
P.S. Thom,
The fact that it is intermittant makes we wonder whether it could be a problem stemming from a cold solder connection on the circuit board for head unit. So may I suggest that you unmount the unit but keep it plugged together. Then take a small screwdriver and while holding the blade end tap on each of the components on the circuit board(s) while watching the display to see if you locate an item that causes the display to change over to the alternative state from which it is currently functioning. Then if you find that examine the all the pads to which the wires of that component are soldered to inspect for a crack in the solder, and in any case reheat all the connections.
Just today I had another ATC owner with the same issue write in, so maybe we can find a generic fault pattern and a common fix.
Roland


Hi Thom,
There are 11 possible codes, 10 of which are related to either a sensor or an actuator failure. The last code, 36, is described as "ATC head communication failure" which in the earlier version of the system ('89 manual) has the simple suggestion "replace the ATC control and retest".
So it appears that if we are to take the result as correct the only choices are to remove the ATC main control unit and examine the circuitry for some obvious burned out components and replace them, or look for a replacement at a pull-it-yourself wrecking yard.
If I had this dilemma I would probably do just that. I wish there were a better prognosis but that is what it appears to be.
Let me know how it goes with your efforts so I can learn and share with others.
Roland