ac compressor not engaging
 

Hi
I never had working AC.
I was told the aux fan was dead which it was.
Also the 50 amp fuse behind the other fuses was blown.
changed the fuse but it blew again.
I have just fitted a second hand fan and it spins up fine.
Now the problem is that the compressor does not engage.
I was wondering if there is a fuse for the compressor.
And i would like to know what voltage fires up the compressor
so that i can jump power to it.
Or does any body know what i could test to find out what could
be wrong.

Thank you in advance.

Dave king

I would bet your low on refrigerant. The low pressure switch isn’t allowing the compressor to engage. How mechanical are you? You could try jumping the trigger wire at the compressor (dunno if it’s pos or neg) and see if the compressor fires up, if it does and it doesn’t get cold, there’s your answer. If your not mechanical, take it in and have it looked at.

Have you run codes with a Foxwell or real BMW scanner? Why does it say the compressor is not engaging? I think it would be highly likely that the fan fuse was blown, preventing the compressor from running, AND you had a second problem keeping the compressor from running as well. A Foxwell would tell you exactly what the problem is.

The clearest thing you have here is that 50A fuse blowing. I would focus on that. Exactly when does it blow? Can you do some experiments where you unplug certain things and see if the fuse does not blow? Yes, you will need some fuses.

And yes, once you get that figured out, you might be low on refrigerant or some other issue may exist. But maybe not. You might have a simple short somewhere.

Hi
the fuse only blew because the fan was dead.
Fan spins as it should and fuse does not blow now.
Will check for gas today.

Thank you

Just put power to the compressor and it started spinning.
ac did not blow cold.

I pressed one of the valves on the ac line and gas came out.
so could the problem be low gas even though it released from the valve.


Thank you

Suggest you take it to a reputable shop to evacuate and recharge the system.

Yes it can be low and still release freon. Grab a can of refill from the auto parts store that comes with a gauge. Put it on and you will know right away if it's low. Be careful not to overfill.

:thumbup:

:iagree:

I agree also because you could have oil slugged your condenser too....

Don't ask how I know...[emoji24]

Sent from my SM-A730F using Tapatalk

Good to hear on the fan fixing the fuse problem. At this point then, it might be a refrigerant issue.

The basic issue on refrigerant is that the system is designed to contain a certain amount of it (by weight), and it is tough to measure how much is in there. Pros have equipment to easily evacuate the whole system, weigh it, and put back in the exact right amount. Without that equipment, the rest of us can only take pressure and temperature measurements and make our best estimates based on those. Not impossible, but not necessarily easy in problem cases, which I think is why you are getting the sound advice to take it to a pro.

I posted something a while ago on freon, which might give a basic understanding of why this pressure issue is not as simple as filling a car tire:
https://xoutpost.com/1166563-post28.html

It's good that you've found you have at least some pressure there. That means you have some refrigerant left, and that positive pressure will have kept contaminants from getting in. If you measure pressure (at the low pressure port, but as @upallnight said, if the compressor is not running and the system is not blocked, pressure will be equal throughout) and it is below that of a saturated vapor, that means you have only gas in there, no liquid. That might be great in that you'd know the system was almost empty and you could make a good guess about how much to add. Vs. the more common DIY-type approach is to keep adding freon until the pressures are right. That might be fine unless there is something else wrong in the system and you would overfill it, not reach the proper pressures, and have a new problem.

On the fan spinning:
There are 3 wires going to the fan. Two thick ones = +12V power and ground. And one thin one. The thin one is a pulse width modulated 12V square wave coming from the ECU. The duty cycle of that square wave is interpreted by the fan controller circuitry (which is built into the motor - take off the cover and you'll see an epoxy-encased circuit board in there) to set the fan spin rate.

This thread here had a lot of info on exactly when the fan should spin, how it is controlled, etc.
https://xoutpost.com/bmw-sav-forums/...-fan-woes.html

But one very simple comment is that if the fan is spinning, the ECU is commanding it by signaling with that square wave on the control wire. No simple grounding or powering that wire (e.g., with a short or jumper) will make the fan spin, as far as I know.

As discussed in that thread I link above, for example, in post #28, you'll see how one of the things that can trigger the fan to spin is removing the pressure switch. So for example (only!), if that switch is damaged or removed, that might tell the ECU to tell the fan to spin at full speed. And who knows, maybe the PO rigged something to make that happen, to prevent overheating, and running the aux fan all the time burned it out, etc, and your problem has nothing to do with AC at all. :dunno:

Not that I think all that is the case, but something like that could be. The whole system is pretty complex. There is a lot of inaccurate info out there on the intertubes. So unless you get lucky, you might want to figure out the whole system or take it to a pro. Or try on here; hopefully you can get the info you need.