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What this BB needs is sound files... Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Wed, 9 Oct 2002 08:44:38
In Reply to: Hey Ari, another seat question....., andy [Profile/Gallery]
, Tue, 8 Oct 2002 22:33:59
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There are a couple of sounds associated with the seat heater controller that are normal.
When you move the little wheel, what you're doing is moving a little piece of spring metal between 3 contacts (no contact for position 0) - a rotary switch. The detents you feel going from 0-1-2-3 are little plastic bumps. It's normal to hear a little (very tiny) click going over the bumps when moving the switch.
From the earlier post, there is a relay in the controller, about an inch behind the wheel. When it opens and closes, it makes a click. When you turn the controller wheel, sometimes you'll hear a click from the relay. During normal operation, the relay opens and closes as it controls the heat. This is normally around once or twice a minute, and is very quiet.
You mention a crackling sound. That sounds like the sound of the relay opening and closing very quickly. This can be due to a few reasons. The first one that comes to mind is the connection between the spring metal of the rotary switch and the contact pads is poor. If that contact is poor, it can confuse the heater controller as to what temp to set the seat to, and you'll hear the relay opening and closing quickly. This also does a poor job of heating the seat. The other possibility is that there is a bad resistor (electronic component) in the controller, one used to provide hysteresis. Hysteresis is a fancy word for providing a slight difference between the turn on and turn off temps. Just as an example, say setting 3 turns the seat heater on if the seat drops below 85 degrees. Hysteresis keeps the seat heater on until the seat gets to 90 degrees, then shuts off. There is 5 degrees of hysteresis. If the resistor that provides this is bad, the relay would close at 84.999 degrees and open at 85.0001. This does a great job of controlling the seat to a precise temperature, but will wear the relay out. You'd hear a lot of clicking.
The seat controller doesn't care about the heating element. If you ask for heat and the element is broken, the relay will close, and stay closed because the seat never gets to temperature. No clicking.
In your position, the first thing I'd do is grab my ohmmeter and slide the seat forward to access the connector under the seat. Check the resistance of the heating element. You'll see in the under 10 ohm range if the element is good, and an open if the element is bad.
I'm suspecting that your element may be just fine, but have a bad ground from the seat heater to chassis. This would be a black wire from the connector to chassis. The temperature sensor and seat heating element share the ground wire, and the heater takes a lot of current. If the ground is poor, it will present a voltage drop under high current. The relay closes, putting current through the heater, and because the ground is poor, the ground point actually increases in voltage. Since the temp sensor shares this ground, it also increases in voltage, which tricks the controller into thinking the seat's too hot, so the controller switches off. This removes the current, and the cycle starts again.
Check your heating element and ground. There is no great way to check the ground without putting a lot of current through it, so the best thing to do is just to pull out the bolt, clean the surfaces with fine sandpaper or Scotchbrite, and bolt it back together.
IF the heating element is bad, resolder it. If you want, replacement pads are available from a variety of places. If you still have a problem, then pop the controller out of the dash, open it up, and clean the contacts on the rotary switch with some alcohol. Make sure the wiper is making good contact.
Quasimotor (http://www.quasimotors.com/) has a nice writeup on seat heaters.
posted by 192.249....
, Tue, 8 Oct 2002 22:33:59, Wed, 9 Oct 2002 08:44:38 <-- Viewing This Message
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