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Old 06-09-2018, 10:51 PM
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Join Date: Sep 2006
Location: Middle TN
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what to do about hot relays?

84SD I was reinstalling the climate push button and sitting with both of the driver side doors open in 90* heat. The car wasn't running. I went to check fuses and noticed that relays A (seat control) and F (window relay) were both hot.

Heat in wiring usually means resistance. How do I systematically search to and remedy the cause? All circuits appear to work.
85SD 240K & stopped counting. 84SD 180,000. Thinking of painting both.
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Old 06-09-2018, 11:16 PM
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The power relays in the fuse box can get pretty hot. They have low resistance coils and dissipate a couple watts worth of heat when energized. The result is a hot can.
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Old 06-10-2018, 12:44 AM
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Location: Sacramento, CA
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Strange if you had not been actuating those relays. I don't know the SD. My 84 & 85 300D have relays only for AC and radiator fan (plus relays built into climate boxes). I assume you aren't talking about the relays on the climate push-button box. Normal Bosch 30 A relays don't get hot from the coil current, maybe slightly warm. If the contacts have too much resistance, they can get hot when flowing a lot of current, but that might mean they are about to die.
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Old 06-10-2018, 07:55 PM
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The front windows in my w124 would work with no key in ignition as long as at least one front door was open , this is a standard feature. Possibly this may be the reason your window relay is hot ?
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Old 06-11-2018, 06:51 PM
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Join Date: Jun 2004
Location: West of Ft. Worth. TX
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If relays get hot while in use, my experience is they are drawing too much current. This can be due an inductive load, such as an electric motor, starting to break down or bind or possibly a grounding problem.
However, if not in use, the relay itself may be breaking down, usually due to an internal diode.

84 300SD 350K+ miles ( Blue Belle )
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