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Originally Posted by bcm
I have an 88 2.3 190e, its obvious a conversion has been done,which leads to the my issue.
Needless to say,I have'nt this car long and its getting hot out so the a/c need to operative.So while while trying to recharge my a/c with an can of "134 mix" the compressor came on about 3sec into the refill then shut off.I tried jumping and still no action.
Should I move on to finding out which sensors are bad or is this a compressor issue?
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BCM,
My 190E manual says "On vehicles as from model year 85 the refrigerant compressor will be activated only after approx. 10 seconds as soon as an engine speed of approx. 600 rpm has been attained (to stabalize the engine speed).
"The control unit compares the two speeds of the ring gear and the refrigerant compressor 2 seconds after the compressor comes on (to compensate for clutch slippage during cut-in). If there is an rmp difference of more than 30% as soon as the compressor comes on, this condition is checked for a period of 200 milliseconds. If the rmp difference equalizes within 200 milliseconds, the compressor remains engaged. If the rpm difference remains, the control unit will immediately cut out the compressor. This process is again repeated when the ignition is switched off and the engine is restarted."
The rpm difference could be due to slippage of the belt or a bad rpm sensor in or at the compressor (not sure exactly where that sensor is). The control unit (behind the battery) could also be bad.
You can remove the control unit and force the compressor to run by putting a wire jumper between pins 5 and 7 of the 12-pin connector where the control unit plugs-in. (Be careful as you can see some sparks if you short pin 5 to ground.) Then measure that the rpm sensor is working with a voltmeter between pins 9 and 11 of the 12-pin connnector and set the voltmeter to AC voltage. It should read about 0.3 vAC at approx 750 rpm. Mine read 0.53 vAC and was OK. Move the voltmeter to pins 1 and 2 of the 12-pin connector, set the voltmeter to DC volts, and you should see approx 8.5V. Mine read 8.4 volts.
If the belt is tight and not slipping, and these voltmeter readings are OK, it could be the control unit, I guess, but don't quote me. Like I said before, I am no expert.