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Old 12-09-2003, 12:53 PM
Registered User
Join Date: Jan 2000
Location: San Francisco, CA, USA
Posts: 46
Question R129 500SL Climate Control Auto Mode and A/C longevity


I was wondering if leaving the climate control on Automatic has any effect (either adverse or beneficial) on the longevity of the A/C system. Would leaving it on E mode most of the time (until AC cooling is needed) be better?

Similar question for my W124 E420: Should I use E mode/low fan most of the time rather than leaving it on A/C witt Fan on Auto?

A mechanic once told me not to run my A/C constantly because it would wear out the compressor prematurely.


2011 C300

Gone but not forgotten:

1995 E420
1990 500SL
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Old 12-09-2003, 01:20 PM
blackmercedes's Avatar
Just a guy
Join Date: Dec 2000
Location: St. Albert, Alberta, Canada
Posts: 3,492
This is a often talked about subject, and there are two schools of thought. The one that is prevailing is that it is healthy for your AC compressor to run. The coolant contains the lubricant for the compressor, and the idea is that when it is running, it is being lubricated and the seals won't dry out.

On 1996- MB AC systems, the AC compressor is a variable pressure system that runs the AC compressor all the time, regardless of ACC temp setting. It simply keeps the evaporator at about 3-4C, using the variable pressure system instead of cycling the compressor on and off. This seems to have increased the overall reliablity of the AC compressor.

On our old 1988 626 I would make sure I ran the compressor during the winter months (in heating mode for dehumidifying) and the AC system is just now requiring service 16 years into the car's life. And the compressor still works perfectly.
John Shellenberg
1998 C230 "Black Betty" 240K
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Old 12-09-2003, 02:32 PM
Join Date: Dec 2001
Location: Southern California, U.S.A.
Posts: 8,508
What Blackmercedes said.

In addition, it is best to not set the wheel to the fully hot or fully cold position, and also to not set the fan flower speed to continuously on "high" or "low", but rather use the "Auto" button.

Drivers have the feeling that full heat or full A/C will get the passenger compartment to the correct temperature fastest.

This doesn't allow the system to work as designed.

To get the longest life from the automatic climate control system, allow the system to exercise all components.

If the temperature inside the car is more than 4 degrees away from the setting on the temperature wheel, the system will use full heat or full A/C regardless.

As the interior temperature approaches the setting at the climate control panel, the automatic functions will slowly reduce blower speed.

Allowing the system to work in its automatic mode, with all components functioning, will prolong the life of the system.

When flap controllers and valves (vacum operated) don't move for long periods, they tend to stick in position and ruin the component.
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".
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