Some help, Power window relay hot question
 

Hi,
81 sc usa.

Power window relay in fuse box is hot, obviously I'm not raising and lowering the windows over and over again to make it so :)
It's warmer than the fuel pump relay, I'd think it should be cool like most other relays.

Anyone come across this before? Is this normal? Any help please to give some direction before I dig in.

thanks,
Phil

If I had this issue I would consider the following while reviewing the schematic diagram of the circuit.

1. The relay overheating is due to a higher than normal current draw within the relay portion or the power window circuit.
2. Test the window motors separately to do this I would add an ammeter in the circuit at fuse 21 (25 amp) to check the current draw while activating each of the three window switches separately. The higher motor current draw would be the side to do a detailed inspection of all connections.
3. Try replacing the relay and/or the individual window switch’s after testing the current draw.
4. Check each of the connections in the circuit for corrosion or heat damage including the ground connections
5. The relay, fuse or switches, window motors could cause the issue due to the age of components and the heat being generated while active.

Pat,
Thanks.

Read your reply, this was what I've done:

1. Looked at schematics/fuse/relay diagram.
2. Pulled fuse for windows, verified that indeed I had the right fuse.
3. Ammeter across fuse box contact points, No current draw with car in run position, which is correct, then checked Ammeter with D battery and 22 Ohm resistor, working and correct.
4. Pulled relay, across two terminals there is an always conducting winding with key in the run position. ~65 Ohms.
5. Did the math, 12*12/65 ~ 2W, that seems about the right amount of heat I was feeling.

I think everything is A-ok. I'm going to check the winding resistance on another relay perhaps, but there is hardly a point.
With 85F temp yesterday, perhaps calling the relay hot in the subject line was a bit of a stretch, it just surprised me that it was warm as the fuel pump relay roughly, till I read about the magnetic winding always being energized.

Phil

I meant that you should put the ammeter in series between the relay contact terminal 87 and the top of fuse 21. Just remove black wire from top of fuse 21 and connect ammeter in series with black wire and top of fuse 21. When you select up or down on any one of the window switches you would record the amp draw. This would allow you to isolate which window motor is drawing excessive current if it is.

One other thought, is the relay getting hot with car running but not exercising the window motors? If the relay is getting hot when ignition is on then the issue could be in the relays coil circuit. The relay coil terminal 86 is energized from the top of fuse 13 (red/white) wire. Relay terminal 85 provides ground for coil brown wire.

Hi Pat,


I was interested in the current being drawn without activating the window switches with the car in the run position but do understand your test, it should be equivalent test setup to what I've done (ammeter in series with fuse 21).
Also, it doesn't mean that a wire with insulation rubbed down and contacting frame won't rattle around while driving in the door causing a temporary periodic short, but unlikely. But at 2W, this relay should warm up for sure, as long as it's not hot.



Phil

There would be no current draw through the relay contacts and fuse 21 without operating one of the three window switches. Your warm relay issue must be the heating of the relay coil. When the car is running are all the relays casing give off the same temp? If not then you have a poor contact issue with the coil of the relay.

You are correct.

One thing, I checked the wiring in Bentley, the power window and fuel pump were the only relays with a coil energized continuously while the car is running, so those two can be compared against each other in terms of warmth to some degree maybe, as the coil resistance may not be equal and the pump does work constantly, so not equivalent either.

Since there is no unexpected current draw, the next step would be to swap in another relay and check if the temperature and the coil resistance are roughly the same.

Phil

On an '81 sc, do the power windows remain operational after the key's turned off but before a door's opened (normal operation on Carreras). If so, worth checking whether your power windows will ALWAYS work with the engine off (even after opening the door) and/or if your dome light circuit doesn't turn on dome lights when a door's opened. On my Carrera, normal operation is for the power window circuit to remain active after ignition is shut off (relay triggered on) but to deactivate when the door pin switch senses a door's open. If the door pin switch has failed/is dirty, then on my Carrera, the power window relay would remain on indefinitely (and slowly drain the battery over the course of a week). If/while always active and drawing power to the relay coil, I'd expect the relay would get/stay pretty warm. FWIW