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  #1  
Old 07-26-2009, 03:15 AM
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tach and AC stopped working

Gentlemen,

I know from a search of the forum that my problem is probably due to a failed "OVP" relay.

Ok. Which one is the OVP, where is it located on a 1985 300SD and how do I identify it?

Thank You,
Joe Marroso

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  #2  
Old 07-26-2009, 09:26 AM
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Quote:
Originally Posted by Joe Marroso View Post
Gentlemen,

Which one is the OVP, where is it located on a 1985 300SD and how do I identify it?
The OVP relay is located in the main fuse/relay panel - driver's side under the hood, and it's the one with the fuse on top.
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'84 300SD 119KMi (Liesl der Diesel)
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'82 300SD 253KMi (new parts car)

Last edited by micalk; 07-26-2009 at 09:28 AM. Reason: clarity
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  #3  
Old 07-26-2009, 11:46 AM
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Even if the fuse is not blown, your relay may be bad. Mine was.
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  #4  
Old 07-26-2009, 12:44 PM
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Originally Posted by pwagon View Post
Even if the fuse is not blown, your relay may be bad. Mine was.
Forgot to mention that. There is a zener diode inside the relay can that seems to die. Mine was dead in my '84 300SD when I bought it, but the one in my '84 300D was good. Location of the relay in the 300D? Behind the passenger side vent. Why? My only guess is a rogue German engineer.
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'84 300SD 119KMi (Liesl der Diesel)
'84 300D 326KMi when the oil left (former parts car)
'82 300SD 253KMi (new parts car)
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  #5  
Old 07-26-2009, 11:20 PM
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fixed!!!

Quote:
Originally Posted by micalk View Post
The OVP relay is located in the main fuse/relay panel - driver's side under the hood, and it's the one with the fuse on top.
Thanks micalk,

It was the fuse. Sometimes life can be kind. By the way, it had a 15amp fuse in it. I replaced it with a 15amp fuse. Will this present problems?

Joe Marroso
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  #6  
Old 07-26-2009, 11:48 PM
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as far as i know it should be a 10 amp fuse. You could blow the relay with a 15.
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  #7  
Old 07-26-2009, 11:49 PM
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All OVPs that I am aware of use a 10 Amp fuse. It is possible that something in your car is drawing too much current and someone previously replaced the blown 10 with a 15, which is not safe.

By finding the blown fuse, you have patched but not fixed your problem. You still have to answer the question, why did the fuse blow in the first place. It could be a patch of insulation missing from a wire or some other occasional short-circuit. It could be a failure in one of the loads (tach, cruise, EGR controller) on the OVP. It could even be a failure in the OVP itself. If the zener diode turns on at too low a voltage, it will cause the fuse to blow. So you need to keep an eye on the replacement fuse.

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