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· 325ic E36 '94
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194 Posts
Discussion Starter · #1 ·
Hi Everyone,

So ever since i've had the car, the air conditioning has not worked. I tried topping it up but that didn't resolve the issue. It seemed to hold pressure though I haven't check recently.

My temperature sensor also isn't working. It randomly tells me strange readings and often says it's below freezing. I've read on here that this could be the simple cause to an air con unit not functioning. Is this the case?

If so, I'm looking for any articles or guidance you can give to give me a dummy run on replacing it / diagnosing it. Please don't assume anything, including where exactly I find the sensor etc :)

I have a 1994 E36 325i Convertible.

Thanks Everyone :)
 

· D'oh, You Kids!
1984 633CSi, 1985 635CSi, 1985 325e, 1987 325is, 1993 325is, 1995 318is, 1995 M3, 2003 F150
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32,075 Posts
Are you talking about the outside temperature readout on the OBC? That reading, and the sensor that supplies the reading, have ZERO to do with the AC system. FYI, the sensor is in the driver's side brake duct behind the front bumper.

Is your AC compressor cycling? When you turn on the AC does the clutch on the compressor engage?
 

· 325ic E36 '94
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194 Posts
Discussion Starter · #5 ·
hey everyone,

so i just went to recharge the gas for the aircon. I just started topping it up and as it got to 30 psi I heard a click and the pressure drop. The clicking sound that used to happen when I turn my air con on and off has now stopped. I know that this is not good news....

what do i do from here?
 

· D'oh, You Kids!
1984 633CSi, 1985 635CSi, 1985 325e, 1987 325is, 1993 325is, 1995 318is, 1995 M3, 2003 F150
Joined
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32,075 Posts
You need to see if the COMPRESSOR clutch is engaging. That is probably the click you heard. The compressor won't engage until the system has a certain minimum pressure in it (I don't know what the cut-off is on BMWs). The noise you hear in the dash is the air ducting doors moving to direct air where you have the controls set, and/or the air recirculate door closing so that the cabin are is recycled instead of trying to cool the incoming outside air.

C'mon you A/C guys, chime in. I understand the system and can work on them, but I can't describe the process very well.
 

· 325ic E36 '94
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194 Posts
Discussion Starter · #7 ·
Awesome. Thanks for the info!

So if that's the case, inside the vehicle it seems that the ducting doors no longer engage/move when i turn the air con off and on. The gass pressure doesn't seem to hold after I just tried to charge it, I think as its old it's given way some where. The click happened either at the point the gass dropped.

How would I check to see if the compressor clutch is engaging?
 

· D'oh, You Kids!
1984 633CSi, 1985 635CSi, 1985 325e, 1987 325is, 1993 325is, 1995 318is, 1995 M3, 2003 F150
Joined
·
32,075 Posts
Look at it. You can see it from below easier than above, but either way, if the pressure is too low in the system, it will not engage at all, ever. The pressure drop is what it's supposed to do when the compressor cycles. You measure pressure from the low pressure side, which is the suction side of the pump. When you start putting a can of refrigerant in, the pressure will rise, since it's the can pressure you're seeing. As the can empties the pressure will drop, but it should be higher than it was before you emptied the can into the system.

What kind of gauge are you using? A two-gauge pro set, or a simple DIY single gauge that came with the can of Freon?
 

· 325ic E36 '94
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194 Posts
Discussion Starter · #9 ·
The simple DIY kit that comes with the freon. So what's happening is as I connected the hose to the low pressure valve, it showed a bottom needle pressure ie none lol. So I started adding it and it rose, as I continued I heard the click and the the gauge dropped to zero again. As I tried adding more the needle simple swings up and straight back down. I'm guessing that this means that it isn't comtainimg pressure and therefore the clutch won't engage?

Where abouts when looking under the vehicle would I find the compressor clutch?
 

· D'oh, You Kids!
1984 633CSi, 1985 635CSi, 1985 325e, 1987 325is, 1993 325is, 1995 318is, 1995 M3, 2003 F150
Joined
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32,075 Posts
If it's dropping that fast, you're wasting your time. You've got a blown seal or hose.

I couldn't find a picture from below, but here is one as viewed from above. The arrow pointing to the clutch is faint but there. the clutch is to the far left:
 

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· D'oh, You Kids!
1984 633CSi, 1985 635CSi, 1985 325e, 1987 325is, 1993 325is, 1995 318is, 1995 M3, 2003 F150
Joined
·
32,075 Posts
I'm not saying it's specifically a hose. Could be any of several seals, too. Your best bet at this point is take it to a pro. Avoid the stealership, though.
 

· D'oh, You Kids!
1984 633CSi, 1985 635CSi, 1985 325e, 1987 325is, 1993 325is, 1995 318is, 1995 M3, 2003 F150
Joined
·
32,075 Posts
I doubt it. With the extremely low to no pressure the system pressure switch never let the pump engage.

Sent from my MB860 using Bimmer App
 

· Registered
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3 Posts
I had a similar issue with my air con too, OP. I charged the system with one of those DIY kits and it started working but it was still too low. I bought some more r134 and put in a little bit more and the system stopped working again. It turns out I accidently overcharged my AC system. I didn't want to deal with that mess, so I took it to get evacuated and recharged to the correct amount/pressure. From what I understand, too low a pressure or too high a pressure will prevent the compressor from engaging. If you had the DIY pressure gauge hooked up with the aircon running full blast the pressure should be lower than if you didn't have the AC running at all. If the compressor is engaged and you are still not getting any cold air, I would reccomend taking it to a pro, I agree with these guys. The AC system is not very DIY friendly if you don't have the correct equipment, it's also very dangerous because of the high pressures and the frostbite potential.
 

· 325ic E36 '94
Joined
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194 Posts
Discussion Starter · #20 ·
ah i see.

Ok well I've now the temp sensor sorted, and it now shows in the 70's which is nice.

I'm now just trying to determine that my aux fan is engaging and spinning with the turning on of the aircon. Am I right in saying that neither through the grill, nor under the hood, can you see if it's spinning without removing some of the protective surround?
 
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