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AC stopped - Could Final Stage Resistor be cause?

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7 replies to this topic

#1 DennisCooper

  • LocationSlough West London/Heathrow
  • Current Car:Ex Police - E39 530d Touring

Posted 29 July 2010 - 04:34 PM

Hi all

6-8 weeks ago, I switched my AC on and I got some cold air and then petered out. I then switched the AC off and had the temperature on the lowest setting and I still got warm/hot air. Classic Final Stage Resistor failure symptoms.

today I had my AC re-charged and switched the AC on and got no cold air. Looking at the engine its clear that the AC compressor is not spinning - could it be possible that as the Final Stage Resistor is kaput, that it knocks out the AC compressor switch on as well?!

I'm hoping by changing the FSR the new part will 'send the signal' to switch the AC compressor on. The machine today said that theres no leaks in the system as it tests the pressure prior to taking the old gas out before refilling.

Anything else I can try or get my mechanic to look at that's common to fail or not work with the AC system?

Cheers, Dennis!
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Tel: 07708 804500 10am-9pm

#2 bigjay

  • Locationsunny southport!
  • Occupation:refrigeration/airconditioning engineer also sitting in my hottub drinking beer

Posted 29 July 2010 - 04:37 PM

The fsr is for the fan inside the cabin and not the a/c comp! When you switch the a/c on is there a load pit on the engine? If so it sounds like you've got a seized comp!!
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#3 Estoril-5

  • LocationBirmingham, West Mids

Posted 29 July 2010 - 05:06 PM

could it be the heater solenoid thingy?
E39 Sport

I like both..but the 42's just give it that edge 8)

#4 mickk44

  • LocationSurrey
  • Occupation:Electrician
  • Current Car:E39 535i se with tasty bits.

Posted 29 July 2010 - 05:18 PM

Is the compressor not controlled by a solenoid clutch that either lets the comp pulley either idle or drive the compressor?
I had an old rover and this happened to me, it was a rather large three pin electronic power switching relay that was not switching the electric clutch.
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#5 ciggy535i

  • LocationGloucester, UK

Posted 29 July 2010 - 07:54 PM

Well, it could be one of many things. Any number of sensors, valves, fans etc. It maight be worth getting the A/C fault codes read.

A common fault is the condenser fan (in front of the radiators) can seize- check it spins freely.

You can apply 12V directly to the compressor briefly. See if the clutch clicks in to rule out this.
1996 E39 535i, V8 and a manual......

#6 Trisman

  • LocationCowfold, Nr.Horsham, W.Sussex.
  • Occupation:Project Management, Construction industry.
  • Current Car:E39 532i Touring. 'E12 M535i.

Posted 29 July 2010 - 08:23 PM

Dunno if this'll help, but I had a failed FSR on a '97 Touring recently.

The blower fans were completely dead, but the compressor was still kicking-in and cold air would dribble out of the vents.

One new FSR (well, second hand!) & it's all working.

So, I reckon the FSR doesn't effect whether or not the compressor clutch will engage or not.


Current: E39 Touring B10 3.2 Alpinalike in Oxford Green.
Alpina 3.2 engine & gearbox mit flappy paddles. 19" Alpina alloys, spoiler & interior.
M5 Brakes, roof-rail delete & stuff.
E12 M535i Kashmir Gold, 16" open-lug Alpina alloys.


E31 850CSi Manual V12 insanity in Orient Blau.

E39 540i Manual in Smurf Bloo.

E24 635CSi manual. Grun. Style 5 Alloys, lowered B5 suspension.

E39 '00 530i Imola Red Sport manual.

E39 '98 528i SE Auto Arctic Silver. (237k miles!)
E28 M5 No.8. Weiss. (Now floating around German eBay).
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E24 635CSi, Blue,
E28 M5, Lach silver.

#7 ally

  • LocationAberdeen
  • Current Car:E39 530i Sport Aegean Blue Edition

Posted 29 July 2010 - 10:59 PM

FSR is nothing at all to do with the AC, if your compressor is not turning, then check the operation of the magnetic clutch, check the fuse & check the system pressure, if you had a bad leak for example, the system would not run as the LP switch would hold it off

2003 E39 530i Sport Aegean Blue Edition

2006 Ford Focus C-Max 1.8 TDCI

#8 DennisCooper

  • LocationSlough West London/Heathrow
  • Current Car:Ex Police - E39 530d Touring

Posted 29 July 2010 - 11:46 PM

Cheers all!

I'll be soon giving my car to my mechanic who'll be able to sort this out for me and a few other little niggly things as well :)

glad the machine did that test today, not sure how reliable it is, but I don't have leaks apparently! hope the fix isn't too pricey !

Thanks, Dennis!
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