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Old 08-01-2006, 01:19 PM
Registered User
Join Date: Jul 2006
Posts: 6
Angry 94 e420 a/c inop

car came to me with a/c inop. we charged and checked, system pressures were very high, compressor would cut in and out. technician assumed this was due to compressor itself. we replaced compressor, drier, switches, including evap temp switch and engine temp switch, and expansion valve. compressor pressures look better now, but the compressor does not want to stay running. i have gotten involved with this since customer is now into this over $1500 and still has no compressor operation. the auxilliary fans are not operating. if i disconnect connectors on blue switch in the front of intake, the fans do come on. i can bridge them to get the fans to come on low speed. i cannot locate a wiring diagram specific to this vehicle. the mercedes dealership across the street is secretly looking to see if they have the diagnostic box to check system. any help is appreciated (my compressor is a nippendenso reman from german auto parts in atlanta.
marie sublett

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Old 08-01-2006, 01:45 PM
slk230red's Avatar
WECO Installer
Join Date: Jul 2006
Location: Tampa, FL
Posts: 819
The auxillary fans have to operate for the compressor to continue running. When the high pressure side climbs to a certain pressure, the high pressure switch on the drier opens and disconnects the compressor until the high side pressure drops.
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Old 08-01-2006, 08:53 PM
Larry Delor's Avatar
What, Me Worry?
Join Date: Jun 1999
Location: Sarasota, Fl.
Posts: 3,114
First thing to check is the resistor for the aux fans. It is behind the driver's side head light, mounted on the wheel well (probably have to move the horn out of the way too). big ole spring in a ceramic housing. The wire on the top likes to fry itself to bits.
It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein

09 Jetta TDI
1985 300D
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Old 08-02-2006, 08:28 AM
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Join Date: Jul 2006
Posts: 6
Thumbs up it's fixed

Thanks a lot for the replies. The car is fixed, the resistor was burnt up. We rewired it. Is there anything to do to keep this from happening in the future. I can not believe how hot that thing gets. Nevertheless, the car is finished and we are putting it back together this morning to prepare for delivery. Sometimes we forget the basics - like check auxilliary fan function when diagnosing any a/c job.....
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Old 08-02-2006, 11:48 AM
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Join Date: Sep 2004
Location: DFW / Collin County Texas
Posts: 1,882
I hope the customer isn't charged for a compressor and other parts that weren't needed.
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Old 08-02-2006, 12:19 PM
Senior Member
Join Date: Sep 2002
Posts: 3,040
Originally Posted by mariesu
Sometimes we forget the basics - like check auxilliary fan function when diagnosing any a/c job...
This reminds me of an old joke.

What did the shop foreman say to the technician?

"Make sure you check the fuse..........LAST!!!

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