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  #1  
Old 11-07-2009, 03:22 PM
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Join Date: Aug 2008
Posts: 212
SL 500 1995 High A/C system pressure reading

Boy this car will test your wits! Installed a rebuilt compressor, expansion valve, drier two weeks ago. Proper oil level and freon charge. System was evacuated by ASE tech friend. Compressor won't engage after it ran fine for a week. System shows "high" pressure, the reading is from the low side valve using a DIY freon install gauge. Pressure shows 90 psi. Last week it showed normal. By passing the high pressure switch with a paperclip won't engage the compressor. During some troubleshooting last week, this worked. After the install, I mistakenly connected the wires at the drier in reverse and the fans ran and the compressor would not. I figured out the wiring goof-aw and everything was fine until today. Fuses are OK but won't run. Steve
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  #2  
Old 11-07-2009, 05:43 PM
82 380SL & 96 SL500
 
Join Date: Jun 2008
Location: Southern Illinois
Posts: 245
Quote:
Originally Posted by Gusfazekas View Post
Boy this car will test your wits! Installed a rebuilt compressor, expansion valve, drier two weeks ago. Proper oil level and freon charge. System was evacuated by ASE tech friend. Compressor won't engage after it ran fine for a week. System shows "high" pressure, the reading is from the low side valve using a DIY freon install gauge. Pressure shows 90 psi. Last week it showed normal. By passing the high pressure switch with a paperclip won't engage the compressor. During some troubleshooting last week, this worked. After the install, I mistakenly connected the wires at the drier in reverse and the fans ran and the compressor would not. I figured out the wiring goof-aw and everything was fine until today. Fuses are OK but won't run. Steve

That is an r134 system? If so, without the compressor running, that
would be about right for both high and low side connections of an equalized system at an ambient temperature of just over 80f.
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  #3  
Old 11-08-2009, 02:10 PM
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Join Date: Aug 2008
Posts: 212
SL500 A/C issues

Thanks for the reply. I received the same answer from a couple of other folks. Another suggestion was made to check and or replace the evaporator temp sensor in the cabin, thought was it could be faulty given the age of the vehicle. Anyone know anything about that? I am going to give up and bite the bullet and likely take it to the dealer at the end of the week.
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  #4  
Old 11-08-2009, 04:34 PM
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Join Date: Oct 2005
Posts: 4,263
Do you have the climate-control pushbutton unit? If so, you can read the evaporator temperature sensor reading to see if it should be replaced. Otherwise, you can measure its resistance and compare to the specs.

Age is of no concern with a ETS. They do simply fail occasionally, and a bad ETS will disable your compressor.
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