 |
|
|
1985-1998 [Subscribe to Daily Digest] |
 | [Main 9000 Bulletin Board | BBFAQ |
Next by Date | Post Followup ]
Member Login / Signup - Members see fewer ads. - Latest Member Gallery Photos
Re: HELP! seat heater switch noise Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Fri, 22 Feb 2002 15:48:42
In Reply to: HELP! seat heater switch noise, RyanR, Wed, 20 Feb 2002 22:10:55 Members do not see ads below this line. - Help Keep This Site Online - Signup |
If the problem were the cabin temp sensor fan, I don't think turning the ACC off would help -I'll bet the little fan runs all the time the ignition is on, not just when the ACC is "ON".
If the problem follows the heater switch - namely, move the switch from one seat harness to the other, and the buzz follows the switch:
The Seat Heater switch does have a relay inside. The relay opens when the seat is warmer than the temp setting, and closes when the seat is too cold. There is a little dead band of a few degrees in there, also called 'hysteresis'. The idea is that the seat actually has to be a few degrees colder than the setting for the relay to turn on, and a degree or two hotter than the setting to turn off.
My first guess would be the hysteresis in the circuitry is missing. Now, hysteresis isn't something that just falls out, but it is usually provided by a feedback resistor. So, you could get a relay 'buzz' if there were a bad solder joint or one of the components on the circuit board have failed. Another, slightly stranger, possiblity is the selector switch. When you turn the knob, a little rotary switch connects different resistors into the circuit, each resistor representing a different seat temp. The rotary switch is just a little metal arm moving over a copper trace on the circuit board. If there is corrosion at that contact, or the metal arm isn't as springy as it used to be, it might make poor contact. If the contact is just poor enough, the vibration from the relay closing could cause the little arm to lift off the solder contact, which would cause the relay to open (click-click). The arm then drops back down onto the pad, causing the relay to close, which bounces the arm back up again, and the cycle continues. This could cause a series of clicks very fast, which sounds like a buzz. This would require *just* the right springiness in the arm, but it could happen.
If the problem stays with the seat, then the solution is probably very simple - fix the ground connection under the seat. The low side of the temperature sensor in the seat shares the ground wire with the seat heater element. If the ground wire at the seat is making poor contact, all that seat heater current will flow back through the low side sense wire into the controller, which would cause an incorrect temperature reading. This could cause the relay to buzz.
Good luck!
posted by 140.157....
, Fri, 22 Feb 2002 15:48:42 <-- Viewing This Message
No Site Registration is Required to Post - Site Membership is optional (Member Features List), but helps to keep the site online
for all Saabers. If the site helps you, please consider helping the site by becoming a member.
 |
 |
 |
 |
 |
