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  #1  
Old 06-02-2007, 01:01 PM
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A/C cools but compressor turns on and off

I'm having trouble with my A/C in my 1995 E300D. The unit is completely charged with 134a. I do not have any leaks in the system but the compressor turns on for about 5 seconds and then turns off. I can be traveling down the road an it will start working great then it will cut off again. The blower motor works fine inside the car. What could be causing the problem?
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  #2  
Old 06-02-2007, 01:43 PM
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Quote:
Originally Posted by Smith1 View Post
I'm having trouble with my A/C in my 1995 E300D. The unit is completely charged with 134a. I do not have any leaks in the system but the compressor turns on for about 5 seconds and then turns off. I can be traveling down the road an it will start working great then it will cut off again. The blower motor works fine inside the car. What could be causing the problem?
Your system has a charge, but it is not fully charged would be the first thing I'd look for. The sight glass is useless with R134 without a manifold gauge set to measure the high and low side. The second thing to look for would be a malfunctioning cold control sensor located after the evaporator under the dash. You should also have a electronic temp thermometer and you can put the probe in your center vent where the air will be coldest and get your readings. My vent temp is 49*F after 10 minuts at full cold in Phoenix when it's 104*F outside! You can get a temp probe at Radio Shack.
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  #3  
Old 06-02-2007, 02:02 PM
Diesel Head
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check your low pressure switch also..if not functioning properly it will cause the compressor to kick off prematurely
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  #4  
Old 06-02-2007, 02:05 PM
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Smile

Quote:
Originally Posted by Knightrider966 View Post
Your system has a charge, but it is not fully charged would be the first thing I'd look for. The sight glass is useless with R134 without a manifold gauge set to measure the high and low side. The second thing to look for would be a malfunctioning cold control sensor located after the evaporator under the dash. You should also have a electronic temp thermometer and you can put the probe in your center vent where the air will be coldest and get your readings. My vent temp is 49*F after 10 minuts at full cold in Phoenix when it's 104*F outside! You can get a temp probe at Radio Shack.
Thanks, this is the 1st time I had any trouble with this car. I bought it new and I have over 400,000 miles on it.
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  #5  
Old 06-02-2007, 02:08 PM
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Originally Posted by Diesel Head View Post
check your low pressure switch also..if not functioning properly it will cause the compressor to kick off prematurely
Where is the low pressure switch located?
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  #6  
Old 06-02-2007, 02:18 PM
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I also for forgot to mention that the tachometer stopped working and it will start working again when the A/C compressor kicks on.
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  #7  
Old 06-02-2007, 02:56 PM
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There is no low-side pressure switch on this car!

I think that your car may have a compressor speed sensor. If there is more than one wire going to the compressor, you do. If so, this may be the cause of your troubles. A dirty sensor can make it appear that the compressor is turning slower than the belt; a loose belt makes this a reality. If you have this sensor and the climate control thinks the compressor is running too slowly for the current engine RPM, it shuts off the clutch current.

Sorry, I missed the comment about the tach. If you have the speed sensor, but no tach input, your AC will also not be happy.
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  #8  
Old 06-02-2007, 03:06 PM
AHH,What's up Doc????
 
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Originally Posted by Matt L View Post
There is no low-side pressure switch on this car!

I think that your car may have a compressor speed sensor. If there is more than one wire going to the compressor, you do. If so, this may be the cause of your troubles. A dirty sensor can make it appear that the compressor is turning slower than the belt; a loose belt makes this a reality. If you have this sensor and the climate control thinks the compressor is running too slowly for the current engine RPM, it shuts off the clutch current.

Sorry, I missed the comment about the tach. If you have the speed sensor, but no tach input, your AC will also not be happy.
OH good lord! I'm sooooo glad to have a 1983 300D W123!!!! Does anyone else feel that more modern electronics only make it overengineered?
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  #9  
Old 06-02-2007, 03:12 PM
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Originally Posted by Knightrider966 View Post
OH good lord! I'm sooooo glad to have a 1983 300D W123!!!! Does anyone else feel that more modern electronics only make it overengineered?
I would, were it not for the fact that my '96 is even more complex than his '95.

I don't have the speed sensor, however, so that's one less thing to go wrong. Instead, the '96 uses a thermofuse in the clutch. If the belt slips, the fuse blows. Then you simply replace the compressor.

But there is an upside. I can see my high-side pressure and temperature, and evaporator and heater core temperatures from inside the car, while driving.
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  #10  
Old 06-02-2007, 03:34 PM
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The inoperative Tachometer may be a clue. See this thread: Particularly post #4 regarding a Klima Relay and Tachometer keeping the A/C from operating...

AC Doest work - where do I start ?
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92 500SL
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  #11  
Old 06-02-2007, 05:37 PM
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Originally Posted by speace View Post
The inoperative Tachometer may be a clue. See this thread: Particularly post #4 regarding a Klima Relay and Tachometer keeping the A/C from operating...

AC Doest work - where do I start ?
OK. where is the KLIMA RELAY located?
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  #12  
Old 06-02-2007, 06:42 PM
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I recommend doing some searches if you haven't already.

Here is another good post on the subject:
KLIMA Basics missing from this forum

I could not tell you where the relay is on your car. Perhaps someone with more specific knowledge will respond?
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02 S500
92 500SL
92 400E
87 300E (Sold)
83 300D Turbo (Sold)
75 300D (Sold)
74 240D (Sold after 20 years)
65 Mustang 5.0 (w/Electronic Fuel Injection)
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  #13  
Old 06-03-2007, 12:22 AM
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Help!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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