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1999 s500 2012 e350
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52 Posts
Discussion Starter #1
98 S420, AC is not working, compressor not engaging, blower works fine, checked the wire to the clutch, with ignition on, engine running AC off and AC on in all cases no voltage in the line, r134 low pressure reading 28, high pressure was not checked , dont have tools for that, climate unit diagnostic showd cabin temp 74 "basement temp" EVAPORT temp 74 "freon" pressure 2 two, jumped the clutch with direct connection to the + battery side and the clutch clicked, engine running clutch jumped AC on the compressor is running, air still hot, r134 low pressure same 28, climate diagnostic cadin temp now 76 EVAP temp 84 and freon pressure 2, so the question is whats the next step and what is the most likely diagnosis

PS: secondary air injection pump keeps coming on and off on its own and I have a P0410 code, dont know if this has anything to do with the AC system

Thanks
 

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Outstanding Contributor Always Remembered RIP
216 with everything. 2002 SL500 with everything. 2009 SL500 with everything.
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6,543 Posts
The air pump has nothing to do with this, I am not good with air con, the things that can cause it are the 2 sensor,1 being on the evaporator
 

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94 S420 RIP 2/8/13 02 ML55AMG, 06 CLS55AMG, 89 Mas. 228, 84 Por. 911 Carrera, 93 Toyota t.t. Supra
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It might be that your a/c unit has no freon. The entire a/c system has a series of pressure switches designed to prevent the unit from working if a certain level of freon isn't present to prevent damage to the compressor. Fill it first. Then start with the diagram of the unit if it doesn't turn on and look for the switches. Or if you can visually see all the of the unit look for what looks like tops with two wires on them as the old oil pressure sending units looked. Good luck.
 

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Outstanding Contributor - Always Remembered, RIP
Zotye Auto 1.5T T600 2016
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52,804 Posts
The pressure sensor is on the dryer, if too little pressure in the system then this sensor will not send the signal to switch on the compressor. It would seem that you either have a bad pressure sensor or this system has little freon gas, time to evacuate the system and refill and then test for leaks.
 

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1999 s500 2012 e350
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52 Posts
Discussion Starter #6
sounds logical but what about the low pressure line reading of 28?
 
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