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Malfunctioning ""REST" Button on A/C Control Panel/Batt Drain

7549 Views 12 Replies 7 Participants Last post by  Ifloru
I've been experiencing battery drain problems with my 92 300SE while the vehicle is not being operated. I thought it was a short that caused the battery to drain. On occassion, I'd see red/blue lights on the center A/C vents light up and thought that it must be because of a short in the electrical system after the car is turned off.

I recently noticed that the "REST" button on my 92 300 SE's a/c control panel lights up after the ignition is turned off. This seems to fire up the defrost fans and results in a drained battery. Does anybody know what the problem is and how to solve it?

TIA
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92 500SEL to 01 E320T current 2014 lexus LS460
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3,885 Posts
The REST button allows the operation of the heater when the engine is "off" I belive the c...

The REST button allows the operation of the heater when the engine is "off" I belive the circulating pump and the blower operate, to keep you warm as long the the coolant in the radiator provides heat.
 

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W140 S class, E31 850Ci, XC90 Exec AWD geartronic
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444 Posts
This turning on itself is a sign of electrical gremlins. I suspect that the battery is on ...

This turning on itself is a sign of electrical gremlins. I suspect that the battery is on its way out and the voltage pulses used by the CC system are being violated.

Connect your battery to jump leads and a donor battery and then start your car. Kill the ignition while still attached to the donor battery and see whether REST kicks in itself. My guess is that it wont while connected to the donor battery. This is a sign that yours is on its way out. Take the battery to a check centre and have it diagnosed. Even one dead cell of the six will cause ignition faults as you describe.
 

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600SEL
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1,093 Posts
This is known problem with early 92 W140 cars. You need to check software status on the ...

This is known problem with early 92 W140 cars. You need to check software status on the pushbutton controller. To check software status push and hold REST button until you see "1" on the left LCD window. Push left AUTO button until you'll get "9" in this window. Right LCD will give you software status. If it is 62 you need to replace pushbutton controller. Another reference is a production date of the push button controller from 3/92 to 9/92
 

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92 500SEL to 01 E320T current 2014 lexus LS460
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3,885 Posts
REST Button

IT applies to Chassis #A055784 to A078197 if you find the code 06 it is the faulty one. 4,5,7 are good and so are 58,59,60. The dealer bulletin number was 83/44
but it seemed to center on the charcoal filter control circuit drawing excessive current. It could be a defective/sticky switch
 

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S-Class 300S
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4 Posts
Discussion Starter · #6 ·
Re: This turning on itself is a sign of electrical gremlins. I suspect that the battery is on

Originally, I thought it was the battery (a 2 year old Benz batt that was exactly 2 yrs old) so I swapped it out for another 64 month battery. Granted, it wasn't a Benz battery but it was working in another vehicle and was fully charged with a battery charger before installation. It was drained in a matter of hours after installation into the Benz and could not muster enough energy to turn the motor over. This leads me to believe that something was draning the battery after the car was turned off.

I think you're on to something about the low voltage and electrical gremlins, though. This is the first time I've seen the REST button light go on. On other occassions, I've seen the red and blue lights on the center A/C vents turn on. BTW, once the REST button goes on, I can't seem to turn it off. I'll try your recommendations and report back here.

This turning on itself is a sign of electrical gremlins. I suspect that the battery is on its way out and the voltage pulses used by the CC system are being violated.

Connect your battery to jump leads and a donor battery and then start your car. Kill the ignition while still attached to the donor battery and see whether REST kicks in itself. My guess is that it wont while connected to the donor battery. This is a sign that yours is on its way out. Take the battery to a check centre and have it diagnosed. Even one dead cell of the six will cause ignition faults as you describe.
 

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S-Class 300S
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4 Posts
Discussion Starter · #9 ·
Re: This is known problem with early 92 W140 cars. You need to check software status on the

This is known problem with early 92 W140 cars. You need to check software status on the pushbutton controller. To check software status push and hold REST button until you see "1" on the left LCD window. Push left AUTO button until you'll get "9" in this window. Right LCD will give you software status. If it is 62 you need to replace pushbutton controller. Another reference is a production date of the push button controller from 3/92 to 9/92
I checked the status and it showed a "62". I guess this means that the pushbotton needs to be changed. How difficult is it to replace the pushbutton? I'd like to do it myself if possible.
 

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1992 S600
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3 Posts
RE: Malfunctioning ""REST" Button on A/C Control Panel/Batt Drain

I have exactly the same problem on my 92 S600. What is the "pushbutton controller"? Is this the whole climate control unit. Local dealer here priced the unit at around AUS$4k. Wow. I have a theory on a workaround. The A/C works ok under normal running conditions - ie key on, engine on etc. Only have the gremlins when ignition key is off. Also, turning key on seems to reset the unit back to normal. So, theory might be to rewire the climate control unit to only operate from switched power. That is, replace permanent 12V supply with a switched 12V supply. That way it cannot turn anything on in error when the key is off. Of course you lose the REST function but that would a small price to pay for not getting a flat battery. Haven't quite figured out how to do this yet but it seems feasible.
Other options gratefully received.
 

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1992 S600
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3 Posts
RE: Malfunctioning ""REST" Button on A/C Control Panel/Batt Drain

The anser to the problem is with http://www.beckmanntechnologies.com/. They advise this is a known problem with the software in the push button unit. Provided this is the only fault, it is possible to replace just the software (a chip) much more cheaply than replacing the whole unit. Now my problem is how to get the unit out from the dash. Can anyone get me started on pulling the unit out?
 

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1 Posts
;604567 said:
This is known problem with early 92 W140 cars. You need to check software status on the pushbutton controller. To check software status push and hold REST button until you see "1" on the left LCD window. Push left AUTO button until you'll get "9" in this window. Right LCD will give you software status. If it is 62 you need to replace pushbutton controller. Another reference is a production date of the push button controller from 3/92 to 9/92
Hi there, do you know if this would work on a 1996 S280?
 

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1993 400 SEL
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206 Posts
I've been experiencing battery drain problems with my 92 300SE while the vehicle is not being operated. I thought it was a short that caused the battery to drain. On occassion, I'd see red/blue lights on the center A/C vents light up and thought that it must be because of a short in the electrical system after the car is turned off.

I recently noticed that the "REST" button on my 92 300 SE's a/c control panel lights up after the ignition is turned off. This seems to fire up the defrost fans and results in a drained battery. Does anybody know what the problem is and how to solve it?

TIA
My 1993 400 sel did the same thing, could hear the blower fan running with keys in my hand and REST light was on...Dead battery ever morning with New Battery...FIXED it with this works perfect >http://www.autohausaz.com/search/pn...SKU_Mercedes&gclid=CLO6hP7j0M0CFZFcfgodifMAWA
 
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