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A/C Runs High Then Low

1K views 11 replies 7 participants last post by  bentso 
#1 ·
I have a 1997 BMW 528i with 112,000 on it. (Runs perfect) I live in the desert southwest if this applies. My AC unit will run on high at 69 degrees with recirculate on or off and sometimes it will drop down (fan speed) to a very low setting yet I haven't touched it. The air stays cold then about 2-5 minutes later it kicks back on high setting and may not do it again for the rest of the day. It does not do this everyday but it does seem to be during much hotter days - my definition of hot is 110 plus. Any thoughts?

Thanks...
 
#4 ·
Yep, FSR is it!
 
#5 ·
Mine does the same - sort of...
Mine always starts out at medium-high. Then after driving a few (3-5) minutes, the fan speed increases to what seems to be "high". In continuous hot weather driving, it seems to repeat that cycle about every 3-5 minutes. I will look into the link posted above. Thanks.
jeff
 
#7 ·
I would bet my entire fortune($27.37 at the moment) that it is the Final Stage resistor. I JUST replaced mine on my 00 528I. In the process I pulled out a LOT OF SH__ that I didn't need to. Try this:

1) Remove the carpeted bolster panel on the passenger side of the trans hump. It is held in place by one phillips screw and slides out toward the passenger seat.

2)Remove the glove box by first disconnecting the little travel cables on each side of the box(The clips pull straight out with a little coaxing and some good needle-nosed pliers). Next, look under the box and you will see that the entire assembly rides on a stationary bar. Loosen the 10mm nuts and the clamps will relax, allowing you to pull the box straight out. There is a courtesy light on the left side that will have to be disconnected)

3) There is a small black plastic conceal panel on the left side of the glove box area that (as I recall) snaps in and out. Remove it by pulling it straight out.

:mad: You will require the services of a double-jointed, ambidextrous, pygmy at this point, but if none is available get a flashlight and look AGAINST THE FIREWALL, near the top of the trans hump, directly in the middle of the dash. Stick your head deep into the passenger foot compartment and peek up to your left----as far forward as you can see.There is an electrical harness plug that you will first have to pull out. It has clips, so be patient and it will wiggle out.

4) Now, the FSR is ready to remove. It simply clips into its location snugly and snaps into place with a large plastic tab in front of it. You should already have your replacement part so you will recognize the piece as soon as you look in there and pull the harness from it.

5)Along the way you'll encounter a little stepper motor(black) and a white bellcrank assembly. DO NOT TOUCH! :tsk: Very important.

6) Snap everything back together and immediately call your chiropractor.

This is not an easy job, but certainly a DIY project. I made mine much more complicated by removing some stuff that resembled a Chinese jigsaw when I tried to reassemble it.
I can't speak for ANY OTHER car or model, but that's how it went on mine. Good Luck
 
#8 ·
What!!?? You didn't take any photos!!??!?!??
;-)
 
#12 · (Edited)
Just wanted to thank everyone who said to replace the Final Stage Unit. I replaced mine today and it works great! :thumbup:

Yes, it does require the body to do a cantilever sort of bend in a most unnatural position, not to mention your arms still have to move about. (I'm not at all flexible, but I still did it). It took only 15 minutes or so, very straightforward, once I realized that I had to look up to see the plug that goes into the FSU. I used pliers to pull out the plug, and lifted the tab to get out the FSU. The link on the 540i6 site was very helpful.

One more thing: the price for the part at Pacific BMW was over 40% less than my local (Dallas) dealer. The part number has changed (and the new unit looks different, it more 'spines' but they're individually thinner) but it's cross referenced in BMWs parts system.
 
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