BrickBoard Archives
The files contained in this listing have been automatically archived from the active forums. Because the vast majority of posts are now in one place, this archive is considered legacy. You should use the SEARCH feature OR choose your topic and select date tabs within the forum you choose.
Re: SEAT HEATERS[700/86] posted by Don Foster on
Saturday, 21 November 1998, at 10:21 a.m.
Larry --
I can speak about repairing the bun warmers in my '86 240 -- I can't assure you they're identical to the 740. I've heard people mention relays for seat warmers, but I've not faced that yet. (But I sure know how to resolder Bosch relays, though!)
On the 240, there are two heaters ("grids") -- one in the bottom, one in the back. They are wired in series (sorta like Christmas tree lights) so if one fails, the other is also off. There's a connector between them.
There's also a connector from the pair to a harness that disappears under the carpet. When I was troubleshooting, I confirmed that 12 volts was present, and (when unplugged) I found the grid resistance was infinite.
(Note -- I don't have the specs, but you should expect resistance somewhere between 3 to 12 ohms, I'd think. 12 ohms means 1 amp of current which means 12 Watts of heat -- not too much. 6 ohms means 2 amps, or 24 Watts, etc.)
When I checked the resistance of the upper and lower grids, I found the lower grid open. I disassembled the seat and seat bottom and removed the grid. On the 240, the grid only extends from the back up to the "buttons" -- so can be pulled without major surgery.
The grid has a small thermostat, about 1/2" diameter by 3/16" thick, as I recall. You can't miss it. One wire had broken off the connection. (Too many fat a**es bouncing too long in that seat, apparently.) I resoldered it and reassembled it.
A month later I was chasing it again -- the same connection had snapped. Evidently, normal flexing exerted too much force, and broke it. I added a 2" pigtail to relieve the stress, and it has been fine for 2 years.