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Thread: 1985 E23 735i HVAC problem

  1. #1
    Join Date
    Jul 2016
    Location
    Venice, FL
    Posts
    18
    My Cars
    1985 BMW 735I

    1985 E23 735i HVAC problem

    I just recently bought a 735i. I bought it from a friend. I know the history of the car i am yhe 3rd owner. Well when i first pick up the car the Ac was functionaly as in air was moving and i could use the climate selector and the blower speed control. But the air was not cole so i took to a friend that is a mechanic and he checked the preasures which were good. But the Compressor doesnt soumd healthy. So i am sure i need to replace that. The problem that i am having is the nothing is working now
    When i select defrost it turns the ac conpressor on and the aux fan turns on and it defrosts the windshield. But if i select anything else nothing happens. If i keep it on Auto ac it will turn on when it wants. For instance if i select auto ac nothing turns on then maybe 20 or 30 mins later it will just come on. Or it may never turn on. I know the fan works cause the defroster is working.but no matter what i have the climate selector on it just doesnt work.

    I have check all the fuses and relays. I have even checked the glass fuse by the glove box. I took the fan speed and temp dial apart and checked contact and it looks good.

    Can anyone shed some light on this?

  2. #2
    Join Date
    Oct 2013
    Location
    Dubai/UAE
    Posts
    127
    My Cars
    1989 BMW E24
    Probably an HVAC Vacuum leak. Check if the Vacuum compressor in the engine works at engine start for a minute or less to build up the vacuum pressure. If not, then you need to fix that; then you need to trouble shoot the vacuum hoses for air leaks one by one from engine to the firewall up to the interior inside the dashboard. You also might have an initial heat core leak which needs troubleshooting as well.
    Use the search function as this subject has been discussed more than once.
    Good luck.

    Sent from my SM-G935F using Tapatalk

  3. #3
    Join Date
    Jul 2016
    Location
    Venice, FL
    Posts
    18
    My Cars
    1985 BMW 735I
    I am not sure i am explaining this correctly. I have searched the forums. Not finding my problem. When i press any of the buttons other than defrost i am not getting a green light above that button and nothing turns on. I am not complaing about wether it comes out what vent. I am stating it isnt powering on

  4. #4
    Join Date
    Jul 2016
    Location
    Venice, FL
    Posts
    18
    My Cars
    1985 BMW 735I
    I fixed it. It was the micro switch and a bad fan relay

  5. #5
    Join Date
    May 2014
    Location
    Seattle, WA
    Posts
    313
    My Cars
    e3 9 12 23 24 32 34
    Nicely done!

  6. #6
    Join Date
    Sep 2018
    Location
    Dallas, TX
    Posts
    3
    My Cars
    1984 BMW 733i manual
    Dwane82,

    Today I had the exact same problem! driving home and at the end of my 4 hour trip the entire a/c just shut off. No fan, no compressor, no auxiliary fan, and no green lights above the a/c control button ( no matter which one was selected). The defrost setting still worked with its amber light but that was it. I have found out that if I took a screwdriver and tapped the face of the control panel it would come back to life usually ( but not all the time), sometimes you have to play with the fan speed setting turning it off and on and then it might work, or sometimes it will turn back on by itself.

    Every time it happens I hear a very loud clicking ( like a relay sticking), I'm wondering if that may be my problem as well.

    Which relay and which microswitch was bad on yours? I'm trying to find the location of them to get started but with it acting up randomly it's quite annoying to track down, any help would be appreciated!

  7. #7
    Join Date
    May 2013
    Location
    Killingworth, CT
    Posts
    562
    My Cars
    '84 733i, 01 X5 00 750iL
    Having to tap and wiggle the blower speed wheel to get the HVAC panel to stay powered up tells you your blower speed microswitch is bad. It rides against the wheel to switch the system on when you turn the wheel up past zero. This repair is heavily documented.
    Steve H.

  8. #8
    Join Date
    Jul 2016
    Location
    Venice, FL
    Posts
    18
    My Cars
    1985 BMW 735I
    Did you ever fix this sorry I never saw this post.

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