1985-1998 [Subscribe to Daily Digest] |
 | [Main 9000 Bulletin Board | BBFAQ |
Prev by Date | Next by Date | Post Followup ]
Member Login / Signup - Members see fewer ads. - Latest Member Gallery Photos
Not sure there's a problem here Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Sat, 13 Jun 2009 23:47:00
In Reply to: update on voltage when AC is on, aaron, Sat, 13 Jun 2009 16:53:59 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The AC setting (Lo or a temperature) doesn't matter - the AC compressor always cycles on and off as long as the outside temp is above 32 degrees F and ECON isn't active.
If the AC fan is on, the compressor is engaged.
First, only worry about the voltage At The Battery.
If the engine is at idle, the car is warm, and the AC compressor is engaged, that is a pretty big electrical load. Seeing 12.7 volts at the battery doesn't sound like a problem. If you bring the engine revs up to 2000 rpm or so, does the voltage increase?
Two points-
Seeing 12.7 volts at the battery with the engine at idle and with the AC compressor on is NOT a problem. If you see higher voltage at the battery (13.0 or more) when the engine is at speed and/or the AC is off, all is well. The battery charges if the voltage is above 12.7 or so. The battery does not have to be charging all the time - it's just fine if occasionally the alternator bus voltage is about the same as the battery charging voltage (12.6V or more) - If the battery spends most of it's time in charge mode, all is well - an occasional trip into non-charging territory won't hurt it a bit.
Now, if you're not getting 13.0 or more at the battery with the engine at well above idle, not too hot under hood, then the alternator might be on its way out.
Second - AFAIK,the EDU voltage display is a terrible thing. It provides suspect information that causes a lot of people to obsess over every little fluctuation. First, it is NOT a precision instrument. Second, it doesn't measure the voltage at the battery - it's going to measure a voltage from some circuit that is loaded down. Wiring isn't perfect, and wiring gets less perfect as cars age. So the EDU is obviously seeing a local voltage drop due to the large current draw of the AC system. The EDU (as others have noted) can read strangely. Can you 'fix' the EDU? Maybe. It was never a great design when new.
If you really need to know the battery voltage, the only decent solution is to wire a voltmeter to the battery. Frankly, the old Current meter is a better measure of charging system health.
The EDU readings need to be taken with a pound of salt. voltage will vary with engine speed, loads, underhood temperature, phase of the moon. Don't use it as an absolute measure. Look for general trends to alert you to problems. For example, the Starting voltage can vary all over the place, varying from car to car. But if the starting voltage of your car starts dropping over time (days, weeks), it's a sign of a battery on the way out. But comparing one car to another is madness.
As to the EDU voltage, if you see something strange, follow it up. You've done that - you've measured the voltage at the battery and all seems OK. So take this as normal operation for your car, and find something else to obsess over. May I suggest DI cassette health or the H1N1 flu?
I seem to have a lot of post replies having to do with the EDU or the temp gauge. Frankly, both can be sources of Too Much Information.
posted by 192.249.47...
, Sat, 13 Jun 2009 23:47:00 <-- 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.
 |
 |
 |
 |
 |
