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Discussion Starter #1
I replaced my A/C compresssor, dryer and expansion valve due to old compressor not kicking in and condensor clutch not engaging.
Now when I engage the A/C it comes on for about 10-15 seconds and the compressor kicks off. Freon pressures are good and engine runs great. I shut car off and repeat the process and the compressor shuts down again in about 15 seconds. A/C starts to blow cold.
Any ideas? Thank You.
 

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Discussion Starter #3
Belt tension is good, pressure switch seems to be functioning properly. My mechanic friend put a by-pass toggle switch in just below steering wheel. I select a/c button on climate control unit (as I would normally would to engage a/c) flip the toggle switch on and a/c comes on and blows cold for hours in the florida heat. This is a temporary fix. Could it be the MAS contol unit? I read on the net that the MAS it does have some a/c compressor functions. Mine is a MAS MODULE 0085458532. What do you think?
Thank You
 

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W124 Moderator
86 190E 2.3L 16V, 2 95 320TE's, 02 S500
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12,758 Posts
It's the speed sensor on the back of the compressor. Any "slip" in the belt and the sensor will kick the compressor out until the car is turned off and re-started.
 

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1990 300e, 1989 300te
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^^^ this is what in was leaning towards. Be careful with the toggle. I've seen a few compressor burn up cause there running all the time.
 

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Discussion Starter #6
Thank You for the reply. It is appreciated. I will check it out. Just a thought about the A/C Compressor Speed Sensor... I also noticed that my rpm's go from nominal idle of 1,000 to about 600-650 when a/c compressor toggle switch is engaged. Could the low rpm's be causing the compressor speed sensor to shut down the compressor? Would bumping up the idle speed do anything for me?
 

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W124 Moderator
86 190E 2.3L 16V, 2 95 320TE's, 02 S500
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12,758 Posts
Idle speed is controlled by the ECU. There is no adjustment for it. RPM should be in the 600-650 range regardless ..
 

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Discussion Starter #8
Thank you for the great input from everyone. We installed another a/c compressor due to the first one making a moderate to loud whinning noise(it was blowing cold).
Now this 2nd compressor has the same problem as the first one which is as soon as the a/c switch on the climate control module is pushed to the on position, the compressor comes on for about 10-15 seconds then kicks off.
Could I have gotten two bad A/C Compressor Speed Sensors on these two different compressors??? My mechanic says the speed sensor has the proper voltage and "pulses"
Thank You.
 

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W124 E420 : W220 S500 : W222 S550
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I had a similar issue and I pin pointed it to the speed sensor. I ordered a new compressor. During the removal of the bad compressor, I noticed a wire that not making connection in the 4wire connector (i think 4). I checked my wiring schematic and sure as "you know what", it was the speed sensor wire that was loose, albeit almost imperceptible .

If I could get in a time machine I would have repaired the wire and left the "not so bad" compressor on the car. Instead, I installed the new one anyway, and have not had the frigid temps since. but it does work

I could not see the plug very well until I began to removed the old compressor, but I have noticed that it is actually visible, just hard to see.

check your wiring

I replaced my A/C compresssor, dryer and expansion valve due to old compressor not kicking in and condensor clutch not engaging.
Now when I engage the A/C it comes on for about 10-15 seconds and the compressor kicks off. Freon pressures are good and engine runs great. I shut car off and repeat the process and the compressor shuts down again in about 15 seconds. A/C starts to blow cold.
Any ideas? Thank You.
 
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