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#1
02-20-2008, 11:25 AM
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Climate control as a diagnostic tool
I came across this great info on using the Climate control unit as a fast diagnostic tool and would like to share.
To get into the diagnostic mode, turn the ignition switch on, set both temperatures to 72 and press and hold the REST button for about 5 seconds or so. Then cycle up/down through the readings by pressing the AUTO button. You will see on the left side of the display an indicator from the list below and on the right side the value . list of indicators: 01 = In-car temp sensor 02 = outside temp sensor 03 = left heat exchanger (heater core) temp sensor 04 = right heat exchanger sensor 05 = evaporator sensor 06 = coolant temp 07 = refrig. pressure in bar 08 = refrig temp sensor (23*9 = 23.9deg C) 09 = nothing 10 = Blower control voltage (great for evaluating blower controller problems) 11 = emissions sensor (B31) e.g. 3.1 = 31.v 12 = sun sensor 4.2 = 4.2v 20 = aux fan control 6.1 = 6.1ma (max 10ma) 21 = engine speed 22 = vehicle speed 23 = Circuit 58d e.g. 99 = 99% of battery voltage 24 = BATTERY VOLTAGE e.g. 12.5 = 12.5v 30 = left rear air conditioning heat exchanger temp sensor (not all vehicles; obviously) 31 = right side 32 = rear evap temp sensor 33 = blower control voltage rear 0.8(MIN) - 6.0(MAX) 34 = left rear temp selector 35 = right side 38 = software status e.g. 37 rear air conditioning 38 = hardware status e.g. 37 , rear air conditioning 40 = control module version software status (?) 41 = control module version menu hardware status 42 = control module variant code 1st number 43 = variant code second number. a problem is to inteprete the value. The climate-control diagnostic manual describes the normal range for all of these. Could anyone having the climate-control diagnostic manual post the ranges?
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1996 E320 since 1/16/08, 171K miles as of Feb 2011 --------------------------------------------------------- 1989 300CE - R.I.P. Dec 29 2007 Other MBs (sold): 1992 300E-24 - 1979 350SLC - 1984 230E - 1990 300CE 
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#2
02-20-2008, 12:30 PM
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#3
02-21-2008, 11:29 AM
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Those are an expanded set of "operational" codes for all W140 cars as of 9/95 and on.
Peter's link takes you to my pages, Menu#15 that gives both operational and diagnostic codes up to 8/95. As you can see MB expanded the readout include some additional operational parameters that could help in diagnosing A/C problems. In both systems, the two 'key' readings come from #5, "Evaporator Temp Sensor" and #7, "Refrigerant Pressure", in bar. (1 bar = 14.7 psi). You can drive along and see the 'health' of your A/C system. #5 should cycle between 37 (or lower) to 43 on a hot day. #7 should cycle between 7 to 16 bar on a hot day. If it does, your A/C is working fine!
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#4
02-21-2008, 11:40 AM
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My read-outs:
05 (evaporator sensor) = 11C = 51.8F 07 (refrig. pressure in bar) = 9 I guess I am having low refrigerant, maybe need to top off. But I'd like to repeat the reading when it gets warmer.
__________________
1996 E320 since 1/16/08, 171K miles as of Feb 2011 --------------------------------------------------------- 1989 300CE - R.I.P. Dec 29 2007 Other MBs (sold): 1992 300E-24 - 1979 350SLC - 1984 230E - 1990 300CE
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#5
02-21-2008, 12:39 PM
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Assuming your readings were just taken on a 'cold' day, then your A/C is low on charge.
On a cool-cold day, #5 should read around 35-37F at the coldest point. #7 will read low also b/c it's cold!
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Linear Mode
