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1994 E320
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17 Posts
Discussion Starter #1
Hi all. I have an A/C problem that I'd be very appreciative for some diagnostic help with. My car is a 1994 E320 sedan. She has 195k miles on her and has been lovingly cared for each mile. Everything is in very good condition on her, except the A/C. All the normal things have been taken care of including the head gasket and wiring harness. I hope to keep her running for another quality 200k miles but need some help...

Here are the symptoms:

1) A/C ALWAYS works when I first start the car each day.
2) It ALWAYS works (very cold) for about 30-45 minutes.
3) At some point, the compressor stops working (fan still blows). The compressor will NEVER cut back in by itself. I'm not exactly sure, but it seems to stop working after some sort of a deceleration or stop (really not sure of this yet). The engine temperature is not too hot (depending on conditions, between 80-100 degrees C). The AUX fans do not kick in (think they're supposed to kick in at 105 degrees C). The outside temperature has not been above 80 degress F here yet.
4) If I cut off the ignition and restart, the compressor will usually start again and the A/C will blow cold. However, it will usually cut off sooner than before--usually in 5-10 minutes. I can continue this cycle (off/on with ignition), but ultimately the compressor does not kick back in.

Last season, the system appeared to be working fine all year. If I have to say, it could have been a tad cooler, but I have a black/black color combo and the temperatures here in DC reach over 100 F in the summer...so I'd say it was working sufficiently well, even if it could have used a slight recharge.

I just had the freon (R134) recharged as the recommended first-step by my MB mechanic. Of course, he put in the UV dye, but said while the freon was low, it was not too low. When I called him back to tell him of my continued problems, he asked that I try to determine when and under what conditions the compressor stops. He indicated that there are MANY sensors, relays and switches that control when the compressor kicks on/off and that diagnosis is usually time consuming.

I'd be very grateful for any ideas. Thanks all.

1994 E320 (current)
1989 300E (previously)
1984 300D (previously)
 

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95 E320 Cabriolet, 140K
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1,332 Posts
One thought... the compressor can kick off of the belt slips. This feature is provided so the belt is protected in the event the compressor starts siezing. The belt is most prone to slipping during acceleration, hence the connection to your diagnostic of having it related to deceleration.

Things to look at are the belt itself or a siezed tensioner. Though the belt may look good, sometimes an old belt stretches to the limit of what the tensioner can accomodate, leaving slack. Try exercising the tensioner to break any corrosion.
 

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1994 E320
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17 Posts
Discussion Starter #3
Belt seems good. Not loose, hard or cracked. Does not slip. Thanks for the info, though. Will keep an eye on it in the future.

Does what my mechanic say about sensors/controllers/replays make sense to anyone?

Regards
 
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