W140 Climate Control "Memory" Issue
09-20-2019, 10:49 AM
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W140 Climate Control "Memory" Issue
I searched and couldn't find anything so apologies if this has been addressed elsewhere.
I'm having an issue with a new-to-me 1996 S320. Basically every time I start the car the climate control starts at the same setting (let's say 61 degrees on one side and 64 on the other). I can readjust it to the temp, fan setting, etc that I want, but when I shut down and restart the car it goes back to the original setting. Thinking it was an issue with the climate control module, I purchased a replacement on ebay and same issue, only that one is stuck on its own "last saved setting" (In this case "Hi" for both zones).
I'm at a loss for what might be busted here. Any ideas?
I'm having an issue with a new-to-me 1996 S320. Basically every time I start the car the climate control starts at the same setting (let's say 61 degrees on one side and 64 on the other). I can readjust it to the temp, fan setting, etc that I want, but when I shut down and restart the car it goes back to the original setting. Thinking it was an issue with the climate control module, I purchased a replacement on ebay and same issue, only that one is stuck on its own "last saved setting" (In this case "Hi" for both zones).
I'm at a loss for what might be busted here. Any ideas?
09-20-2019, 05:34 PM
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I've replaced the climate control module (in the panel) and still have the same issue. Is there another module I'm unaware of that's malfunctioning? Seems like a long-shot to get two faulty climate control modules experiencing the same failure.
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08-19-2020, 08:26 PM
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I was living with this for awhile but am ready to tackle it again. Unfortunately I can't go through the version coding process because it requires setting left side to "Hi" and right side to "Lo" then cycling the key. Since my climate control resets to the previous temperature settings I can't enter into the version coding process.
I'm thinking about trying/buying another unit from ebay, but having 2 climate controls with the same uncommon failure seems like a longshot. Could there be another explanation aside from the climate control? Considering I have 2 units that exhibit the same issue, it feels like I could be throwing good money after bad.
I'm thinking about trying/buying another unit from ebay, but having 2 climate controls with the same uncommon failure seems like a longshot. Could there be another explanation aside from the climate control? Considering I have 2 units that exhibit the same issue, it feels like I could be throwing good money after bad.
Last edited by hankster2; 08-20-2020 at 12:50 AM.
06-18-2021, 02:35 PM
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Just thought I'd bump this to see if anyone else has any input. With 3 different climate control head units tried, I've confirmed that's not the issue and because of the nature of the issue I can't enter the "Version Coding Process". Everything in the "diagnostic values" seems OK.
Is there a process for evaluating the individual wires in the wiring bundles coming into the climate control head unit? Perhaps I have a bad ground, short, etc. feeding the unit?
Is there any other "brain" associated with the climate control unit?
As indicated the issues are that:
a) the climate control resets to the same random setting every time the car is restarted. For each head unit I tried it's different (whatever setting it was set on in the last car it was installed in I'm assuming).
b) A/C doesn't work (compressor doesn't kick on)
c) "Residual Heat" feature doesn't work
Is there a process for evaluating the individual wires in the wiring bundles coming into the climate control head unit? Perhaps I have a bad ground, short, etc. feeding the unit?
Is there any other "brain" associated with the climate control unit?
As indicated the issues are that:
a) the climate control resets to the same random setting every time the car is restarted. For each head unit I tried it's different (whatever setting it was set on in the last car it was installed in I'm assuming).
b) A/C doesn't work (compressor doesn't kick on)
c) "Residual Heat" feature doesn't work
07-13-2021, 11:45 PM
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Quick update on this in case it helps anyone else someday. Got it mostly working.
I acquired the wiring diagram for the climate control here (Link) . The diagram I have says it's for a '96 S320 (which my car is) and it appears mostly correct except the wires sometimes go to different pins on the climate control module plugs than what I observe. The wire colors appear to be more accurate.
I figured the "always hot" wire would be the most suspect in this case. This wire is Red/Green and jumpers off of the "always hot" leg of the Auxiliary Coolant Pump Relay. According to the diagram this is powered upstream by fuse #18, but I did not find that to be the case. Verified in the climate control plug that Red/Green is not currently powered with the car on or off. I jumpered this off of a power source and was able to get the climate control to "retain" the settings when the CC is turned off. This should allow me to try the version coding process referred to above so one step figured out.
Next I'll track down why Red/Green is not getting power then try to figure out what's causing the AC to not kick on. The car is straight, original owner, and doesn't look like it's ever been modified or in incompetent hands.
I acquired the wiring diagram for the climate control here (Link) . The diagram I have says it's for a '96 S320 (which my car is) and it appears mostly correct except the wires sometimes go to different pins on the climate control module plugs than what I observe. The wire colors appear to be more accurate.
I figured the "always hot" wire would be the most suspect in this case. This wire is Red/Green and jumpers off of the "always hot" leg of the Auxiliary Coolant Pump Relay. According to the diagram this is powered upstream by fuse #18, but I did not find that to be the case. Verified in the climate control plug that Red/Green is not currently powered with the car on or off. I jumpered this off of a power source and was able to get the climate control to "retain" the settings when the CC is turned off. This should allow me to try the version coding process referred to above so one step figured out.
Next I'll track down why Red/Green is not getting power then try to figure out what's causing the AC to not kick on. The car is straight, original owner, and doesn't look like it's ever been modified or in incompetent hands.
