NO AC light (or operation) at switch (help!)

[redbull]

Perhaps some one can help (a new guy on this fourm)... I just obtained a '93 (E34) that does not have any AC activity when the "snowflake" button is pushed. No light laminates on the button, and I do not hear the compressor engage. All fuses are good, so I suspect it is something basic I'm missing?

I appreciate your help. Thanks! ;)

~ John

[Blitzkrieg Bob]

It's probably the refrigerant

The low pressure switch kills the circuit when the refrigerant is too low to operate.

get the system checked for leaks

[redbull]

It's probably the refrigerant

The low pressure switch kills the circuit when the refrigerant is too low to operate.

get the system checked for leaks

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Hum, I read a few things on the forum, and I am now confused on which type of refrigerant my (September 1993 525i) uses? Is there any way to tell?
Oh, even if the refrigerant was too low, don't you think the light would illuminate, and the AC try to engage? Their does not seem to be any circuit that knows the refrigerant level, this would be measurable once the pump (try) to engage and no pressure is determined... but I base this knowledge on other (non BMW) vehicles.

Thanks!! I really appreciate your reply and anyone else wishing to chime-in!

[JonE]

Bob's right, most likely you need refridgerant. Yours shouldn't be the more expensive R12. Time to get it checked out.

[redbull]

Bob's right, most likely you need refridgerant. Yours shouldn't be the more expensive R12. Time to get it checked out.
--

Well OK then... I will add refrigerant and see, but something still does not compute why the switch would not operate (or the recirculate button).

[Beemr750]

It will not work without blower running

[wingman]

It will not work without blower running

Yes true. Couldn't this be a really simple thing like the switch is jiggered? Just be aware Red Bull that to get the switch out you've got to pull the radio out. Welcome to the board by the way.

[redbull]

Yes true. Couldn't this be a really simple thing like the switch is jiggered? Just be aware Red Bull that to get the switch out you've got to pull the radio out. Welcome to the board by the way.

Oh ya, the radio... that I suspect I need a special tool (or are they just Allen keys) The BMW use to be for "Brake My Window" to rip-off the radios, so I wonder if they have a "special" tool now. Thanks for the help... I will try to access th button to do a circuit by-pass to see if I can get the compressor to engage. (and yes I had the blower on, just replaced the resister so now I have several power positions, not just high-speed!)

Funny thing, I am a BMW mechanic for the two-wheel Beemers, so all this AC stuff is new areas.Much to learn... :D ~John

[Blitzkrieg Bob]

on the drier cuts the power to the circuit when the pressure is too low or zero. Killing the ol' Blue Snowflake.

This is to protect the compressor from running without refrigerant that is needed to help circulate the oil.

[Blitzkrieg Bob]

work

[Bill R.]

r134a, there is no confusion, the fitting don't even remotely resemble each other. The first thing you need to do is put a gauge on the system and see what the static pressure is to determine if its low on freon.
The low pressure switch in the system will not let it turn on until a minimum pressure of 2-2.4 bars approx. 30psi minimum. Odds are that you are simply low on refrigerant. The low pressure switch will keep the light from illuminating, an yes many other vehicles use a similar low pressure switch on the filter drier assy to turn the compressor on and off.
The low pressure switch cuts the compressor out to protect it from a couple of things. One thing is if the pressure is too low then the suction side of the compressor can have the freon condense to liquid and piston compressors will not pump liquid, this is called slugging when this happens and it destroys the compressor.. I have a nifty picture somewhere of a honda i was working on that was slugged.




---
Hum, I read a few things on the forum, and I am now confused on which type of refrigerant my (September 1993 525i) uses? Is there any way to tell?
Oh, even if the refrigerant was too low, don't you think the light would illuminate, and the AC try to engage? Their does not seem to be any circuit that knows the refrigerant level, this would be measurable once the pump (try) to engage and no pressure is determined... but I base this knowledge on other (non BMW) vehicles.

Thanks!! I really appreciate your reply and anyone else wishing to chime-in!