LX450 Air Inlet Servo Issue RESOLVED (1 Viewer)

Joined
Nov 17, 2018
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166
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Erie, PA
I'm the new owner of a moderately neglected but not abused or modified 1997 LX450 w/lockers. I've been lurking here for a year and working on the normal issues with these... the info here has been great!
I have something to add now that may be of interest to those with the automatic climate control:
My air inlet (fresh/recirc) vent would cycle continuously when in RECIRC..worked ok in FRESH.
I began by taking out the servo and checking the limit switching tracks which stop the motor in the right place..I tested it on the bench with a 12v battery and it worked as it should. I then checked the 3 wires that connect to it...Yellow is 12V, Light Blue is the RECIRC ground signal from the Auto AC Amp and Light Blue/White is the FRESH ground signal from the Auto AC Amp. Here's where I see the problem...the FRESH ground never goes away which is fine when in FRESH but when in RECIRC the motor now has two ground paths and never stops. The culprit is a shorted switching transistor on the Auto AC Amp board (That white box up near the drivers right knee). T407 is the RECIRC switch and T405 is the FRESH switch.
I replaced T405 and resolved it. I could have used a proper substitute if I knew how to do that but since I didnt I found and ordered three E1A3Q transistors (label on original) from China (Ebay) for $8 shipped. Of course, you can replace the whole Auto AC Amp instead. Mine had some minor corrosion that I first suspected and cleaned but it was the transistor failure in the end. The row of 5 transistors also switch GROUND for other things to do with the Auto Climate but I'm only sure what T407 and T405 do. I just followed the traces to the connector on the circuit board and used the EWD to confirm that A12 Pin 8 is FRESH and A12 Pin 9 is RECIRC. Ive read some other threads that talked about the same issue only with the FRESH position...its likely a shorted RECIRC transistor T407. They are pretty easy to remove and replace..a solder sucker helps.
AC Automatic Amp.jpg
 
Joined
Feb 4, 2004
Messages
136
Location
Cornelius NC
mine has been broken for a long time, haven't had time to look into it until now.
how hard is it to remove the above box from under the dash? does the dash have to be removed?
thanks for sharing this knowledge!
 

NLXTACY

Wits' End
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Dec 7, 2007
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West Hills, CA
It’s very common to have corrosion on the board because if you have a leaking windshield it will usually drip right on top of that box. I’ve opened up some to see a 1” nasty corrosion line that luckily was able to be cleaned up after a few solder repairs.
 
Joined
Feb 4, 2004
Messages
136
Location
Cornelius NC
I've got this issue too. Any chance someone might know the part # of the 'white box by the driver's right knee'?
also what is the best way to get to this box? from under the dash? remove the radio?
thanks,
Faron
 
Joined
Nov 17, 2018
Messages
166
Location
Erie, PA
I removed and reinstalled mine MANY times in the process of fixing the recirc vent issue above. I just did it from under the dash where your right knee sits. The radio isn't even close. I wouldnt say that its easy but I got good at it...and wrecked my neck for a month. It has three connectors that have to be removed before you can free it. This white box is called the AC automatic amplifier....dont know the part #.
I drilled a hole in the bottom of the case to drain any future water......that was not the issue with mine but I could see that water had sat inside the lower half inch of mine at some point. Just as NLXTACY said....a windshield leak drips right in.
 

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