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Old 09-03-2003, 03:57 PM
Registered User
Join Date: Jul 2003
Location: Northbrook,Ill
Posts: 3
Air Conditioning 1988 300TE

I bought this car recently and discovered that the previous owners mechanic hot wired the a/c compressor direct to the fuse box. the a/c now runs all the time as the switch has been bypassed. Any ideas as to why they would have done this and a possible fix for the compressor so the system works properly.

Thank's for any help.
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Old 09-03-2003, 04:07 PM
sixto's Avatar
smoke gets in your eyes
Join Date: Jun 2000
Location: SF Bay Area
Posts: 18,745
Do a search on Klima relay. Lots of diagnostic fodder under that topic.

95 S420
91 300SE
87 300SDL
83 300SD
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Old 09-03-2003, 05:19 PM
Registered User
Join Date: Jun 2000
Location: Plano, TX
Posts: 2,476
Probably hotwired because the compressor kept cutting out. There are many root causes behind the dreaded compressor drop out syndrome. Fortunately they are usually not too difficult nor expensive to address once one actually understands how the system works. Sixto's search recommendation is a good one. I might add "compressor clutch gap" and "rpm sensor" in addition.

Strongly suggest you un-hotwire the compressor. In addition to freezing up the evaporator, if the compressor locks up it will take the serpentine belt with it. No belt, no water pump nor alternator. Doesn't seem worth taking the chance.

- JimY
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Old 09-03-2003, 08:27 PM
Registered User
Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
To say nothing of frying a compressor low on freon.....

Leading cause of compressor dropout is a bad speed signal, usually caused by a slipping belt. This in turn is usually a bad belt tensioner, the rubber part croaks. Pricey, but you will only need one for the next 200,000 miles.

Unwire it, connect correctly, and check the refrigerant pressures, then see what it does. Lots of talk about AC this summer, surely you will find something. If not, post again!

1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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