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Old 05-30-2006, 06:12 AM
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a\c problem

My 90 300e has a intermittent a\c problem it will work just fine then out of the blue stops colling and i checked the comp and it is not engaging any help or comment would be nice thanx jimbo

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Old 05-30-2006, 01:07 PM
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Join Date: Aug 2004
Posts: 44
First thing to do is get a set of gauges and check the refrigerant pressures on the low and high side to see if you are low on refrigerant.

You should be seeing ~35psi on the low and ~150psi on the high side for R134 (a little less for R12 which is what your model year originally was charged with - pressures observed will depend on the ambient temperature) on a fully charged system when the engine is running. If it is substantially lower on both sides, you need to add R134/R12 in incremental amounts until the pressures approach these levels, whatever is in your system. An auto shop should be able to do this if you are unsure how to check the levels and/or recharge.

Sounds like you are low on refrigerant to the point where the compressor cycling switch is not engaging the compressor clutch. If this is the original a/c system, there are several places where refrigerant can leak out - o-rings, compression fittings, compressor seal, evaporator and/or condenser. A leak test and or repairs is the ideal solution but can get expensive on an older car.

Or you could have a bad cycling switch - that is why checking the refrigerant level is helpful - if it is fully charged, then you have a faulty switch or failing clutch on the compressor.

Last edited by rickpark; 05-30-2006 at 01:13 PM.
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Old 05-30-2006, 02:21 PM
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Join Date: Oct 2005
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Does the '90 use a cycling switch at all?

I believe that he might have a compressor speed sensor. If so, that's a very likely candidate.
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Old 05-30-2006, 04:43 PM
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Location: DFW / Collin County Texas
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When the A/C stops all of a sudden, try this: Turn the engine off, remove the key, then restart and see if the A/C works again. If so, your A/C clutch end gap may be out of spec, or the belt may be too loose resulting in slipping. Once the sensor detects slippage, it shuts off power to the compressor until the ignition has been cycled off and back on.
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Old 05-30-2006, 11:16 PM
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Join Date: Oct 2005
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Just a wild guess, but does this service bulletin apply to you? It's a bulletin from the 1999 C230 list, but maybe it's the same.

Number - DDAF83_30-U-6000A
Date - 990818
Title - Occasional Air Conditioner Failure

Syptom - The a/c system will run for approx. 10 minutes, then the a/c compressor will switch off, and then run again for 10 minutes after ignition is again switched on.

Solution - Remove, install evaporator temperature sensor (B10/6)

Good luck,

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