Rear Defrost slows things down???

[fordktpjoe]

OK so last night, (actually 3:00 this morning) I am leaving work, and there's frost on all the windows...yada yada yada...anyway I set the heater to "Defrost" (more on that in a bit) and turn on the rear defrost. Well, I notice I ain't getting much air thru the upper dash vent! WTF? Also the heater motor isn't blowing fast (on the floor) like it normally does after I switch back to "floor". So after a few minutes I drive away, and the turn signals blink VERY slow when I turn them on. After the rear window is clear, I turn off the rear defog, and WOW! the heater motor gains a LOT of speed, and at the next light the turn signals are back to their regular speed too!

At first I thought weak alternator, but wouldn't the headlights have been dim too? They seemed OK and never changed.

So as a test I hit the rear defog switch again, and BAM! everything slows down again! Anyone have any ideas?

Also, why would I not be getting much air thru the front defrost vents? (the upper dash vents) I can feel it coming thru, but just barely. I get GREAT air thru all the other vents, it's warm, just not much volume, it doesn't blow hard.

Oh yeah I have the ATC, which only works in the "Auto" mode. I looked for the resistor everyone talks about, but couldn't seem to find it, anyone have a pic?

[Grandmarchris]

You might want to get the battery tested. Or check the wiring of the rear defroster

[gadget73]

sounds like your battery or alternator are dying on you. The rear defrost does pull a fair amount of current. If the charging system or battery aren't up to the task, it will suck the voltage down pretty badly. You could check it easy enough, turn all the stuff on and check the battery voltage. It could also be a bad connection at the starter relay. The inside of the car is powered off a couple of those connections on the relay, crud there could be causing a voltage drop.



The blower resistor is under the hood, sort of behind the passenger side valve cover. Its not really easy to see. The plug is on the firewall, the resistor itself is inside the heater plenum. 2 screws attatch it from the engine compartment side. Check the wiring first before you pull it out. It could be a bad connection. Normally if the resistor has failed, you'll get high speed only for fan speeds. If you get nothing at all, its usually a connection problem, or the switch inside is dead.

as for the airflow, probably one of the air doors in the dash is messed up. Mine is pretty much the same. Air everywhere, but barely a trickle out of the defrost. Mine also will push air out of the dash in defrost and floor. I'm suspecting a busted air door but haven't pulled it apart to verify.

[86GmLsCoupe]

The rear defroster seemed to always create the largest draw for me, but I think the lowest line on mine may have a break. Whenever I'd turn it on my lights would dim and the blower would slow. I just installed the 3g and when testing it I noticed the rear def. did not dim the lights or slow the blower anymore.

[fordktpjoe]

Well, I wanted to do a 3G install on my car, but I don't have that "post" on the back of my alternator everyone mentions, I only got two plugs, and from reading some posts, it seems like I'd have to do some re-wiring.

[86GmLsCoupe]

It's really not bad to do, I'm gonna take some pictures and try to do a decent write-up of how mine is setup. The post you're talking about is the on the 3G, the older one uses the plug which is a very poor setup that can catch fire. When you convert you just abandon the old wiring, thats all. All that old output plug really is is two thin gauge wires with some fuse links on it (other wire is stator but 3g plug takes care of that), and they wrap all the way around the front of the car (behind header panel), and fuse together into one slightly thicker wire just before going one the starter solenoid. The output stud design eliminates that. The alternator will also bolt right in place of your stock 2G (65 amp). You should definitely consider the upgrade.

[fordktpjoe]

Aight 'den, I'll be watching for a write up and some pics!