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  #1  
Old 04-17-2019, 08:12 AM
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Air conditioning preconditions

Hello people, new member here. I'm sorting out some issues with my new-to-me 2002 4.6is. I recently replaced my radiator, upper and lower hoses, and coolant temp sensor in the lower hose. Ever since, my air conditioning hasn't worked. I used to use it every day up until now. The compressor clutch is not engaging. The snowflake light does illuminate on the HVAC panel, and the engine RPM increases the idle by about 50 rpm when AC is turned on.

Can this really be a result of the work I did with the coolant system? Or is it just a coincidence, or better yet an act of spite by the E53 gods...

-My aux fan does not do an initial spin on cold start
-If high pressure AC switch is unplugged, I do get super high speed aux fan


I've read a lot of conflicting things on this forum about the preconditions needed for compressor clutch activation. Some say the fan matters, some say it doesn't. Some say the coolant temp sensor plays a role, and for some reason air pockets in the coolant can even cause the AC to not activate. I'm hoping someone really has a definitive answer. Am I missing something here that can be related to my cooling system work?

My next step is to get the proper equipment to scan all ecu's for DTC's. I'm guessing there should be something relevant stored in either DME or in the HVAC system. Hopefully I can get something this week to scan it.
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Old 04-17-2019, 10:48 AM
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Your going to need a scan tool to diagnose it since the compressor is controlled by the dme.

If its not happy it wont come on. To turn on initially it requires the pressure on the pressure sensor and a good aux fan circuit. I say good because the fan can be fried but it has to be plugged in. If the dme doesn't see the fan it wont turn on the compressor. The fan can be bad as in doesn't spin but it has to see the fan.

That part is a bit hard to call since a non spinning fan can be caused from it not being plugged in which will cause the compressor to not be turned on.

The fan can be fried in a way that makes it not show up to the dme thus no compressor engagement.

But the fan can be fried but in a way that shows up to the dme as plugged in but not functioning which in that case it will turn on the compressor.

So a scan tool is pretty much required.
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Old 04-17-2019, 10:49 AM
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Oh and if all else fails and I mean as an absolute last resort you can do this....

AC Compressor Manual Override | Crowz Nest
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Old 04-17-2019, 12:38 PM
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Quote:
Originally Posted by Crowz View Post
Your going to need a scan tool to diagnose it since the compressor is controlled by the dme.

If its not happy it wont come on. To turn on initially it requires the pressure on the pressure sensor and a good aux fan circuit. I say good because the fan can be fried but it has to be plugged in. If the dme doesn't see the fan it wont turn on the compressor. The fan can be bad as in doesn't spin but it has to see the fan.

That part is a bit hard to call since a non spinning fan can be caused from it not being plugged in which will cause the compressor to not be turned on.

The fan can be fried in a way that makes it not show up to the dme thus no compressor engagement.

But the fan can be fried but in a way that shows up to the dme as plugged in but not functioning which in that case it will turn on the compressor.

So a scan tool is pretty much required.
I was able to scan my car with INPA today, and didnt have any relevant codes. Only codes for my Mass Air in the DME and no codes in the IHKA.

Since my fan spins when I disconnect the AC pressure sensor, would you agree that the circuit is good enough for the DME to see it? It doesnt seem to spin on first startup as a "self check" though, but I would think there would be a code stored if the DME couldn't see it.

I guess my next step is checking refrigerant pressures. Anyone in North NJ have a set of gauges?
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Old 04-17-2019, 02:11 PM
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You don't need gauges to know if it has enough Freon to work or not.

Go into the scan tool and read the ac pressure. Its in volts. Give me the number and I can tell you the pressure it is seeing.
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Old 04-17-2019, 02:43 PM
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I would said it could be releated to the work you done.

First check a few easy things first. Is the outdoor temperature about 60 deg f (a lot of European cars a/c will not turn on unless is is about 60 deg). But on the my e53 the ac light will come on regardless.



2. is the vent knob in the center vent turn to cool (or blue). The center counter vent "temp control" can over ride the digital control. I freak out once when I had the digital tem control on 80 and the vent will still blows cool before I realized it was set to cool (or blue).



But assuming this is not it. I would look at the thing you did perhaps you disconcerted something by mistake that would be my guess. I would spend some time look at the area I do work to make sure everything is in place.





because

So it work before


and now the the clutch would not engage and the a/c light will not come on. If you are low on freon you clutch still will engage and the a/c light will come on. Unless you are zero on freon. by way it is not freon it the 134a stuff.



And I would check to see I have some freon in the system as one of my first to do.
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Old 04-17-2019, 03:10 PM
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Originally Posted by blaubenz View Post
and now the the clutch would not engage and the a/c light will not come on.

The clutch won't engage, but the AC light does come on
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Old 04-17-2019, 03:15 PM
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Quote:
Originally Posted by Crowz View Post
You don't need gauges to know if it has enough Freon to work or not.

Go into the scan tool and read the ac pressure. Its in volts. Give me the number and I can tell you the pressure it is seeing.
Thank you Crowz, I'll get the pressure number as soon as I can. currently need to borrow someone's equipment to scan so i only have limited availability. I didn't think to get that number when I was in there.

I did get a chance to run the output test for the electric fan, and it seemed to work fine. i think it can be ruled out completely now.

I also confirmed that the AC button on the HVAC panel is registering, so there's that.
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Old 04-17-2019, 03:23 PM
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the light always comes on, even if there's no cooling/drying due to too low ambient temp, no cool air due to too low gas content or other failures. The light just tells you that 'should all be well, then it will cool/dry the incoming air'. It does not prove that the ac system is ok and running like a charm.
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Old 04-17-2019, 03:30 PM
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Quote:
Originally Posted by Roy32 View Post
The clutch won't engage, but the AC light does come on

I am going with what I know about general a/c (not specific to e53) but...



well if the wire(s) to the clutch is disconnected the clutch will not engage and the light will still many be on. Did you do all you can to see everything is still connected?? If the outside temperature is below 60 deg f the clutch may not engage and the light will still be on. You are in the east cost is it like 50 deg outside when you tried.



IF you have zero freon the clutch may not engage. Were you able to confirm that you have some pressure in your a/c system??? The freon is added through a valve like your tire (except bigger). If you don't have any guages you can see if you have at least some freon by removing the dust cap and press the valve stem to see if some freon is coming out (like you tire). Or you can get one of those cheap 134a charging kit that have a guage on it and it will have instructions on now to check and charge you a/c system. But I don't think low pressure is you problem. The clutch should still engage in low freon.
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