'87 300TD Power Seat Relay Stays Hot

[BrierS]

Though I have pulled the ice-cube for now, each time I put a relay (tried 2-3) back in the seat functions are working yet the relay heats up and stays hot. Any advice on where to look first? Thanks.
Steve

[MrCjames]

Is your dome lamp working with the doors? Open a door-dome lamp lights......close the door-dome lamp goes out after 5 or so seconds..

[BrierS]

Originally Posted by MrCjames

Is your dome lamp working with the doors? Open a door-dome lamp lights......close the door-dome lamp goes out after 5 or so seconds..

Yes. The dome lamp is working properly and goes out within seconds after the door is closed.
Steve

[MrCjames]

When you open a door does the radio come on ? I distinctly recall this symptom on the 126 chassis, the 124 is ???able. If the radio does come on than I feel you may have power seat diode problem (shorted), try removing fuse number 2 and reinstall the relay. If you discover that the relay becomes energized upon reinstalling than your problem could be a bit more involved.

Let's see what you come up with

[BrierS]

The radio does not come on when I open the door. I will try what you suggested with the fuse & relay. I believe we are seeing is possily too much power being drawn through the relay. What seems odd though, is that all with the relay in, all functions of the power seat and head rests work properly. It is as if something continues to draw current (possibly excessive) while the motors are supposed to be at rest. It would be easier to understand if a motor continued to work after the switches returned to their respective neutral position.

Thanks for taking the time to think about and respond to my situation . . .
Steve

[MrCjames]

If your seats are working with the key off and the doors closed than there is a problem with the relay staying energized. The relay should only be energized with the key on (15R circuit) OR when either of the front doors are open. If your seats are only working with the "Key On" or "Doors Open" the circuit is working correctly, relays do get hot when they stay energized.

The aluminum relays tend to be a little warmer due to the metal having better conductive properties than it does insulating properties. Energized relays conduct heat, when a relay is hot it does not imply that there is an electrical problem unless the current draw is too high. When the current is too high the fuse that protects the circuit burns, by default this helps eliminate unwanted "Carbecues!"

[BrierS]

Just put the relay back in and checked to see if the seats worked with the key off. They do. They work with the key removed. I checked the owner's manual and it states that is normal operating for the '87 300TD.

I failed to think about your point regarding the fuse being the safety net. The fuse has never blown (that I am aware of) so I should have just left the relay in. I noticed the heated condition last year when I was switching relays for my ice-cube AC bypass. Not thinking it through nor having the experience, I thought hot indicated a problem.

I'll let you know if the car goes up in flames . . .

Thank you again for taking the time to help lead me through this. While plugging on that I took the driver's front interior panel off, lubed the window tracks/rails and gears, put some waxlit on the glass scrapers, resecured two areas of the vinyl trim, removed a piece of 1/8" board the PO had put between the door and the panel (he didn't have the panel properly secured so must have not liked the extra squeaking) cleaned and put dielectric on all terminals, took the seat switch apart watching all the small parts hit the floor, put that back together, reinstalled everything put the relay back in and . . . now it all works. These cars are so much entertainment.

Steve

[MrCjames]

Originally Posted by BrierS

Just put the relay back in and checked to see if the seats worked with the key off. They do. They work with the key removed. I checked the owner's manual and it states that is normal operating for the '87 300TD.

It would be unusual to have the power seats operate with the key off, I believe the battery would die within a day or two if the vehicle is left sitting. Perhaps the owners manual makes a reference to the seats being capable of operating once a front door is opened. "Opening either front door" or turning the ignition switch to "on" typically energizes the power seat relay thus enabling both front seats to operate.

What nationality is your car? European, Canadian or US?

[BrierS]

Pulled the diode, opened it and it is done for. Anyone know the value of the diode so I can solder a new one in? Not certain this is going to be the cause of my power seat problem but at least it is one more thing that needs to be fixed.
Thanks
Steve

[BrierS]

The diode a/k/a silicon rectifier or switching diode is a 1N4003. If my research is correct that would be 200V, 1.0A and hopefully a Radio Shack stocked item. Gotta love the internet.

Hope this helps someone else in the future.
Steve

[MrCjames]

Hm, that seems odd....................perhaps in response number 4 I missed something. Oh well.

[BrierS]

I don't think you missed anything. You correctly questioned the ability to power the seats with the key removed and door closed. I must have misread the manual. The diode is w/o question shot since it is in two pieces. That does not mean that I did not break it when removing it though. I think the fact that when I pulled the fuse that is energized at all times and could not get the seats to work at all, this lead me to the diode. Since power should pass to the relay from fuse #9 with the key anywhere from acc > start and it is not, that meant the diode was shot. Pulled it and found it to be broken. I tried to get one from a local shop this morning but they did not have that size. Possibly tonight I can get one from Radio Shack and solder it in. I'll let you know.
Thanks.
PS I still do not understand how a working diode versus a non working one changes the energizing from fuse #2.

[MrCjames]

Fuse two connects to a 15 circuit (power with key on), the relay would be activated by this source only after the key was turned to the "on" position. The diode is placed in line with the fuse 2 power source and relay socket number 4. The door switches are also connected to socket 4 of the relay. When a front door is "opened" the relay is activated by the power supplied through fuse 9 (circuit 30-power at all times). When the power flows from fuse 9 the diode acts as the border patrol, every electron stops there to avoid problems on the fuse 2 line. A shorted diode allows fuse 2 to become powered up when a front door is "opened." An open diode would interupt seat operations with the key on.

As I understood your posts your seats seem to operate all the time "key off" and "front doors closed" At this time I would like to redirect my thoughts back to response number 4 to see if I miscommunicated something. If I did, please help me understand how I could have communicated this differently so as to keep the diagnostic process simple.

"When you open a door does the radio come on? I distinctly recall this symptom on the 126 chassis, the 124 is ???able. If the radio does come on than I feel you may have power seat diode problem (shorted), try removing fuse number 2 and reinstall the relay. If you discover that the relay becomes energized upon reinstalling than your problem could be a bit more involved."

I see that line number 3 can be misinterprted since it really pertained to 126 chassis cars, none the less when you install the relay if it energizes than line 4 holds true. The problem may be a little more involved.

[BrierS]

I have to slow down and think when I read . . . I thought you meant when I open the door the radio come on w/o me touching the switch. After reading what you wrote a couple of times, visiting my fuzzy schematic, I just went out and opened the driver's door, pushed the switch on the radio and as you stated, it came on. Phew. That's a relief, though I don't know why. I was unable to get a diode tonight so that will have to be a tomorrow project. Thanks again. I'll start new after I have soldered a new one in place of the broken (open) one.
Steve

[BrierS]

Replaced the diode tonight and the relay remains hot, the radio turns on with the door open while the key is out of the ignition, and the seats move under the same circumstance as the radio. This one has me puzzled.