Central Locking System & AC Question

[Ron MB]

1991 500 SL R129
The locking system locks all Doors, compartments ect. using the IR or the Key. When locking the vehicle the lights do not flash nor does the horn sound, is there a problem or is this normal for this vehicle.

AC question, Every time I start the car the AC is on and haft to shut it off using the 0 button is this normal for this vehicle. I'm a new owner as June of this year.

Thanks in advance,
Regards,

Ron MB

[RConrad]

RonMB

Let me know what you find out about the A/C problem. I have a 97 SL-320 with a simular problem. When i turn the a/c on and set a temp., it continues to run full bore until it freezes up. I have to keep cycling it with the switch. This IS NOT normal, as my brother has the same car without this problem. The compressor never gets a signal to cycle on and off normally.

Ron Conrad

[tecqboy]

Ron:

When locking the doors with the remote, only the red led's will flash in the door handles and on the trunk. The horn does not sound and the headlamps do not flash. There is no visual indication that the alarm system is armed ( i.e. no blinking light ).

It is not normal for the HVAC system to go from O (off ) into automatic mode when the ignition is cycled. Do a search of this forum for lots of info on the HVAC system. ( R129 and HVAC is a good start.) Keep in mind that the system changed through the years, especially after 1995 models. But it is possible to get the system to display error codes with the correct combination / sequence of pressed buttons on the unit.

RConrad: Do a search. You may have a bad temperature sensor. A common problem.

[Ron MB]

The AC works fine at least I think it does. When you shut the AC OFF it should stay OFF even an it does until you start the car again, then the AC or heat whatever you had it set on before comes on once again. You would think OFF is OFF until you turn it on.

Thanks again tecqboy (I'll do a forum search bad Temp sensor )

[bobterry99]

RonMB: your climate control is working as designed. I would suggest setting the blower speed to the lowest setting to lessen the annoyance.

RConrad: you can run diagnostics on your climate control to diagnose your problem. Steve Brotherton wrote an article explaining how to do this in the "DIY Articles" section of this website. I would guess that your in-car temperature sensor is faulty.

[tecqboy]

I never use the OFF function. I use the AUTOMATIC function in summer when I want the AC to run and I use the ECONOMY mode when heat or unheated fresh air in desired. Even with the top down, I like fresh air from the floor and dash vents and of course on those cool days I like it warmed. I've read posts from other owners who've said simply that MB designed this system for a luxury car: "just set it at AUTOMATIC 70 degrees and never touch it again". But I can't think of any circumstances to ever switch it OFF.

[Ron MB]

The technical information on this forum is great.

Thanks, Ron